posix: Fix wordexp WRDE_APPEND to preserve state on non-NOSPACE errors (BZ 34090, CVE-2026-6368)

  The previous implementation saved a copy of the wordexp_t struct at
entry and blindly restored it on error via (*pwordexp = old_word).
This is incorrect when WRDE_APPEND is set because w_addword may have
called realloc on we_wordv during partial processing before the error
was detected.  If realloc relocated the buffer, the saved we_wordv
pointer is dangling; restoring it causes a use-after-free in the
caller (e.g. via wordfree), and the relocated buffer is leaked.

Fix this by duplicating the we_wordv pointer array at entry when
WRDE_APPEND is set, so that all subsequent realloc calls inside
w_addword operate on the copy.

This change also fixes a POSIX conformance issue: if the WRDE_APPEND
flag is specified, pwordexp->we_wordc and pwordexp->we_wordv shall
not be modified.

Also fix two pre-existing error return paths in the '"' and '\'' cases
that returned directly from w_addword failures instead of going through
do_error, which would leak the saved array (and previously would also
skip the word cleanup).

A new test (tst-wordexp-append) exercises the changes:

- we_wordc and we_wordv pointer preserved on WRDE_BADCHAR/WRDE_SYNTAX
- we_wordv pointer stability when realloc relocates the buffer
- original words remain accessible after a failed append
- successful append still works (regression)
- recovery: successful append after a failed one
- repeated failures do not corrupt the state
- error without WRDE_APPEND still cleans up properly
- WRDE_BADCHAR on the first character (no partial w_addword)
- WRDE_APPEND into an empty (zeroed) wordexp_t

Checked on x86_64-linux-gnu and i686-linux-gnu.
---
 posix/Makefile             |   1 +
 posix/tst-wordexp-append.c | 307 +++++++++++++++++++++++++++++++++++++
 posix/wordexp.c            |  64 +++++++-
 3 files changed, 364 insertions(+), 8 deletions(-)
 create mode 100644 posix/tst-wordexp-append.c
  

Ping.

On 22/04/26 09:24, Adhemerval Zanella wrote:
> The previous implementation saved a copy of the wordexp_t struct at
> entry and blindly restored it on error via (*pwordexp = old_word).
> This is incorrect when WRDE_APPEND is set because w_addword may have
> called realloc on we_wordv during partial processing before the error
> was detected.  If realloc relocated the buffer, the saved we_wordv
> pointer is dangling; restoring it causes a use-after-free in the
> caller (e.g. via wordfree), and the relocated buffer is leaked.
> 
> Fix this by duplicating the we_wordv pointer array at entry when
> WRDE_APPEND is set, so that all subsequent realloc calls inside
> w_addword operate on the copy.
> 
> This change also fixes a POSIX conformance issue: if the WRDE_APPEND
> flag is specified, pwordexp->we_wordc and pwordexp->we_wordv shall
> not be modified.
> 
> Also fix two pre-existing error return paths in the '"' and '\'' cases
> that returned directly from w_addword failures instead of going through
> do_error, which would leak the saved array (and previously would also
> skip the word cleanup).
> 
> A new test (tst-wordexp-append) exercises the changes:
> 
> - we_wordc and we_wordv pointer preserved on WRDE_BADCHAR/WRDE_SYNTAX
> - we_wordv pointer stability when realloc relocates the buffer
> - original words remain accessible after a failed append
> - successful append still works (regression)
> - recovery: successful append after a failed one
> - repeated failures do not corrupt the state
> - error without WRDE_APPEND still cleans up properly
> - WRDE_BADCHAR on the first character (no partial w_addword)
> - WRDE_APPEND into an empty (zeroed) wordexp_t
> 
> Checked on x86_64-linux-gnu and i686-linux-gnu.
> ---
>  posix/Makefile             |   1 +
>  posix/tst-wordexp-append.c | 307 +++++++++++++++++++++++++++++++++++++
>  posix/wordexp.c            |  64 +++++++-
>  3 files changed, 364 insertions(+), 8 deletions(-)
>  create mode 100644 posix/tst-wordexp-append.c
> 
> diff --git a/posix/Makefile b/posix/Makefile
> index a5e5162c61..1ee73b0b65 100644
> --- a/posix/Makefile
> +++ b/posix/Makefile
> @@ -329,6 +329,7 @@ tests := \
>    tst-wait3 \
>    tst-wait4 \
>    tst-waitid \
> +  tst-wordexp-append \
>    tst-wordexp-nocmd \
>    tst-wordexp-reuse \
>    tstgetopt \
> diff --git a/posix/tst-wordexp-append.c b/posix/tst-wordexp-append.c
> new file mode 100644
> index 0000000000..6253520c57
> --- /dev/null
> +++ b/posix/tst-wordexp-append.c
> @@ -0,0 +1,307 @@
> +/* Test for wordexp with WRDE_APPEND flag.
> +   Copyright (C) 2026 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <wordexp.h>
> +#include <string.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +
> +#include <support/check.h>
> +#include <support/support.h>
> +
> +/* Attempt to force realloc to relocate the we_wordv buffer by placing an
> +   allocation right after it.  Returns a pointer that must be freed after
> +   the test.  */
> +static void *
> +place_blocker (void)
> +{
> +  void *p = xmalloc (0x1000);
> +  /* Write to it so the compiler cannot optimize it away and the allocator
> +     actually commits the pages.  */
> +  memset (p, 0x41, 0x1000);
> +  return p;
> +}
> +
> +/* Verify that all words in we match the expected NULL-terminated
> +   array.  */
> +static void
> +check_words (const wordexp_t *we, const char *const *expected, int line)
> +{
> +  size_t i;
> +  for (i = 0; expected[i] != NULL; i++)
> +    {
> +      TEST_VERIFY (i < we->we_wordc);
> +      TEST_COMPARE_STRING (we->we_wordv[we->we_offs + i], expected[i]);
> +    }
> +  TEST_COMPARE (we->we_wordc, i);
> +}
> +
> +#define CHECK_WORDS(we, ...) \
> +  do {								\
> +    const char *const expected_[] = { __VA_ARGS__, NULL };	\
> +    check_words (we, expected_, __LINE__);			\
> +  } while (0)
> +
> +/* Test 1: WRDE_APPEND + WRDE_BADCHAR preserves we_wordc.  */
> +static void
> +test_append_badchar_preserves_count (void)
> +{
> +  printf ("info: test_append_badchar_preserves_count\n");
> +  wordexp_t we = { 0 };
> +
> +  TEST_COMPARE (wordexp ("one two three", &we, 0), 0);
> +  TEST_COMPARE (we.we_wordc, 3);
> +
> +  size_t saved_count = we.we_wordc;
> +
> +  /* ')' triggers WRDE_BADCHAR and  "extra" would be a new word if the
> +     expansion succeeded, exercising the w_addword path before the error
> +     is detected.  */
> +  TEST_COMPARE (wordexp ("extra )", &we, WRDE_APPEND), WRDE_BADCHAR);
> +  TEST_COMPARE (we.we_wordc, saved_count);
> +
> +  wordfree (&we);
> +}
> +
> +/* Test 2: WRDE_APPEND + WRDE_BADCHAR preserves the we_wordv pointer even
> +   when internal realloc would move the buffer.  */
> +static void
> +test_append_badchar_preserves_pointer (void)
> +{
> +  printf ("info: test_append_badchar_preserves_pointer\n");
> +  wordexp_t we = { 0 };
> +
> +  /* Use many words so that the initial we_wordv allocation is
> +     non-trivial and a later realloc is more likely to move it.  */
> +  TEST_COMPARE (wordexp ("a b c d e f g h", &we, 0), 0);
> +  TEST_COMPARE (we.we_wordc, 8);
> +
> +  char **saved_wordv = we.we_wordv;
> +  size_t saved_count = we.we_wordc;
> +
> +  /* Place an allocation right after to make realloc move the buffer.  */
> +  void *blocker = place_blocker ();
> +
> +  TEST_COMPARE (wordexp ("append )", &we, WRDE_APPEND), WRDE_BADCHAR);
> +  TEST_COMPARE (we.we_wordc, saved_count);
> +  TEST_VERIFY (we.we_wordv == saved_wordv);
> +
> +  free (blocker);
> +  wordfree (&we);
> +}
> +
> +/* Test 3: After a failed WRDE_APPEND the original words are still accessible
> +   and correct.  */
> +static void
> +test_append_badchar_words_intact (void)
> +{
> +  printf ("info: test_append_badchar_words_intact\n");
> +  wordexp_t we = { 0 };
> +
> +  TEST_COMPARE (wordexp ("alpha beta gamma", &we, 0), 0);
> +  CHECK_WORDS (&we, "alpha", "beta", "gamma");
> +
> +  void *blocker = place_blocker ();
> +  TEST_COMPARE (wordexp ("delta )", &we, WRDE_APPEND), WRDE_BADCHAR);
> +  free (blocker);
> +
> +  /* Words must still be intact.  */
> +  CHECK_WORDS (&we, "alpha", "beta", "gamma");
> +  /* The NULL terminator must still be present.  */
> +  TEST_VERIFY (we.we_wordv[we.we_offs + we.we_wordc] == NULL);
> +
> +  wordfree (&we);
> +}
> +
> +/* Test 4: Successful WRDE_APPEND still works (regression test).  */
> +static void
> +test_append_success (void)
> +{
> +  printf ("info: test_append_success\n");
> +  wordexp_t we = { 0 };
> +
> +  TEST_COMPARE (wordexp ("hello", &we, 0), 0);
> +  TEST_COMPARE (we.we_wordc, 1);
> +
> +  TEST_COMPARE (wordexp ("world", &we, WRDE_APPEND), 0);
> +  TEST_COMPARE (we.we_wordc, 2);
> +  CHECK_WORDS (&we, "hello", "world");
> +
> +  wordfree (&we);
> +}
> +
> +/* Test 5: Successful append after a failed append — the implementation must
> +   recover and allow further use of the wordexp_t.  */
> +static void
> +test_append_success_after_failure (void)
> +{
> +  printf ("info: test_append_success_after_failure\n");
> +  wordexp_t we = { 0 };
> +
> +  TEST_COMPARE (wordexp ("first", &we, 0), 0);
> +  CHECK_WORDS (&we, "first");
> +
> +  void *blocker = place_blocker ();
> +  TEST_COMPARE (wordexp ("bad |", &we, WRDE_APPEND), WRDE_BADCHAR);
> +  free (blocker);
> +
> +  /* State must be exactly as before the failed call.  */
> +  CHECK_WORDS (&we, "first");
> +
> +  /* A subsequent successful append must work.  */
> +  TEST_COMPARE (wordexp ("second third", &we, WRDE_APPEND), 0);
> +  CHECK_WORDS (&we, "first", "second", "third");
> +
> +  wordfree (&we);
> +}
> +
> +/* Test 6: Multiple consecutive failed appends do not corrupt state.  */
> +static void
> +test_append_multiple_failures (void)
> +{
> +  printf ("info: test_append_multiple_failures\n");
> +  wordexp_t we = { 0 };
> +
> +  TEST_COMPARE (wordexp ("keep this", &we, 0), 0);
> +  CHECK_WORDS (&we, "keep", "this");
> +
> +  size_t saved_count = we.we_wordc;
> +  char **saved_wordv = we.we_wordv;
> +
> +  void *blocker = place_blocker ();
> +
> +  /* Each of these bad characters must leave the state unchanged.  */
> +  TEST_COMPARE (wordexp ("x )", &we, WRDE_APPEND), WRDE_BADCHAR);
> +  TEST_COMPARE (wordexp ("x |", &we, WRDE_APPEND), WRDE_BADCHAR);
> +  TEST_COMPARE (wordexp ("x ;", &we, WRDE_APPEND), WRDE_BADCHAR);
> +  TEST_COMPARE (wordexp ("x &", &we, WRDE_APPEND), WRDE_BADCHAR);
> +  TEST_COMPARE (wordexp ("x <", &we, WRDE_APPEND), WRDE_BADCHAR);
> +  TEST_COMPARE (wordexp ("x >", &we, WRDE_APPEND), WRDE_BADCHAR);
> +
> +  free (blocker);
> +
> +  TEST_COMPARE (we.we_wordc, saved_count);
> +  TEST_VERIFY (we.we_wordv == saved_wordv);
> +  CHECK_WORDS (&we, "keep", "this");
> +
> +  wordfree (&we);
> +}
> +
> +/* Test 7: WRDE_APPEND with WRDE_SYNTAX error (unterminated quote) also
> +   preserves state.  */
> +static void
> +test_append_syntax_error (void)
> +{
> +  printf ("info: test_append_syntax_error\n");
> +  wordexp_t we = { 0 };
> +
> +  TEST_COMPARE (wordexp ("original", &we, 0), 0);
> +  CHECK_WORDS (&we, "original");
> +
> +  char **saved_wordv = we.we_wordv;
> +  size_t saved_count = we.we_wordc;
> +
> +  void *blocker = place_blocker ();
> +  /* Unterminated double quote triggers WRDE_SYNTAX.  */
> +  TEST_COMPARE (wordexp ("\"unterminated", &we, WRDE_APPEND), WRDE_SYNTAX);
> +  free (blocker);
> +
> +  TEST_COMPARE (we.we_wordc, saved_count);
> +  TEST_VERIFY (we.we_wordv == saved_wordv);
> +  CHECK_WORDS (&we, "original");
> +
> +  wordfree (&we);
> +}
> +
> +/* Test 8: Error without WRDE_APPEND still works (regression test for the
> +   non-APPEND code path in do_error).  */
> +static void
> +test_no_append_error (void)
> +{
> +  printf ("info: test_no_append_error\n");
> +  wordexp_t we = { 0 };
> +
> +  /* Simple failure without WRDE_APPEND.  */
> +  TEST_COMPARE (wordexp ("bad |", &we, 0), WRDE_BADCHAR);
> +
> +  /* After failure without WRDE_APPEND the struct should be safe to
> +     reuse — start fresh.  */
> +  TEST_COMPARE (wordexp ("ok", &we, 0), 0);
> +  CHECK_WORDS (&we, "ok");
> +
> +  wordfree (&we);
> +}
> +
> +/* Test 9: WRDE_BADCHAR on the very first character (no partial words added
> +   before the error).  */
> +static void
> +test_append_badchar_immediate (void)
> +{
> +  printf ("info: test_append_badchar_immediate\n");
> +  wordexp_t we = { 0 };
> +
> +  TEST_COMPARE (wordexp ("hello world", &we, 0), 0);
> +  CHECK_WORDS (&we, "hello", "world");
> +
> +  char **saved_wordv = we.we_wordv;
> +  size_t saved_count = we.we_wordc;
> +
> +  /* The bad character is the very first byte — no w_addword call happens
> +     before the error.  */
> +  TEST_COMPARE (wordexp ("|", &we, WRDE_APPEND), WRDE_BADCHAR);
> +  TEST_COMPARE (we.we_wordc, saved_count);
> +  TEST_VERIFY (we.we_wordv == saved_wordv);
> +
> +  wordfree (&we);
> +}
> +
> +/* Test 10: WRDE_APPEND into an empty wordexp_t (initial call uses WRDE_APPEND
> +   with a zeroed struct — unusual but allowed).  */
> +static void
> +test_append_into_empty (void)
> +{
> +  printf ("info: test_append_into_empty\n");
> +  wordexp_t we = { 0 };
> +
> +  /* First call with WRDE_APPEND on a zeroed struct.  The implementation
> +     must handle we_wordv == NULL gracefully.  */
> +  TEST_COMPARE (wordexp ("solo", &we, WRDE_APPEND), 0);
> +  TEST_COMPARE (we.we_wordc, 1);
> +  CHECK_WORDS (&we, "solo");
> +
> +  wordfree (&we);
> +}
> +
> +static int
> +do_test (void)
> +{
> +  test_append_badchar_preserves_count ();
> +  test_append_badchar_preserves_pointer ();
> +  test_append_badchar_words_intact ();
> +  test_append_success ();
> +  test_append_success_after_failure ();
> +  test_append_multiple_failures ();
> +  test_append_syntax_error ();
> +  test_no_append_error ();
> +  test_append_badchar_immediate ();
> +  test_append_into_empty ();
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/posix/wordexp.c b/posix/wordexp.c
> index 4a8541add4..119ce05d9c 100644
> --- a/posix/wordexp.c
> +++ b/posix/wordexp.c
> @@ -35,6 +35,7 @@
>  #include <scratch_buffer.h>
>  #include <_itoa.h>
>  #include <assert.h>
> +#include <intprops.h>
>  
>  /*
>   * This is a recursive-descent-style word expansion routine.
> @@ -2212,6 +2213,12 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags)
>    char ifs_white[4];
>    wordexp_t old_word = *pwordexp;
>  
> +  /* When WRDE_APPEND is set we work on a copy of the we_wordv array so that
> +     the caller's original pointer is never invalidated by realloc inside
> +     w_addword.  The saved_wordv keeps the original; on success we free it,
> +     on non-NOSPACE error we free the working copy and restore the original.  */
> +  char **saved_wordv = NULL;
> +
>    if (flags & WRDE_REUSE)
>      {
>        /* Minimal implementation of WRDE_REUSE for now */
> @@ -2246,6 +2253,23 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags)
>  	  pwordexp->we_offs = 0;
>  	}
>      }
> +  else if (pwordexp->we_wordv != NULL)
> +    {
> +      /* WRDE_APPEND with an existing word list: duplicate the array so that
> +	 realloc during parsing does not invalidate the caller's pointer.  The
> +	 strings themselves are shared.  */
> +      size_t num_p;
> +      char **dup;
> +      if (INT_ADD_WRAPV (pwordexp->we_offs, pwordexp->we_wordc, &num_p)
> +	  || INT_ADD_WRAPV (num_p, 1, &num_p))
> +	return WRDE_NOSPACE;
> +      dup = __libc_reallocarray (NULL, num_p, sizeof *dup);
> +      if (dup == NULL)
> +	return WRDE_NOSPACE;
> +      memcpy (dup, pwordexp->we_wordv, num_p * sizeof *dup);
> +      saved_wordv = pwordexp->we_wordv;
> +      pwordexp->we_wordv = dup;
> +    }
>  
>    /* Find out what the field separators are.
>     * There are two types: whitespace and non-whitespace.
> @@ -2326,7 +2350,7 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags)
>  	    error = w_addword (pwordexp, NULL);
>  
>  	    if (error)
> -	      return error;
> +	      goto do_error;
>  	  }
>  
>  	break;
> @@ -2344,7 +2368,7 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags)
>  	    error = w_addword (pwordexp, NULL);
>  
>  	    if (error)
> -	      return error;
> +	      goto do_error;
>  	  }
>  
>  	break;
> @@ -2410,10 +2434,15 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags)
>  
>    /* There was a word separator at the end */
>    if (word == NULL) /* i.e. w_newword */
> -    return 0;
> +    {
> +      free (saved_wordv);
> +      return 0;
> +    }
>  
>    /* There was no field separator at the end */
> -  return w_addword (pwordexp, word);
> +  error = w_addword (pwordexp, word);
> +  free (saved_wordv);
> +  return error;
>  
>  do_error:
>    /* Error:
> @@ -2424,11 +2453,30 @@ do_error:
>    free (word);
>  
>    if (error == WRDE_NOSPACE)
> -    return WRDE_NOSPACE;
> +    {
> +      /* we_wordc and we_wordv are updated to reflect any words that were
> +	 successfully expanded.  The old array is obsolete.  */
> +      free (saved_wordv);
> +      return WRDE_NOSPACE;
> +    }
>  
> -  if ((flags & WRDE_APPEND) == 0)
> -    wordfree (pwordexp);
> +  if (flags & WRDE_APPEND)
> +    {
> +      /* POSIX 2024 states that for in other error cases, if the WRDE_APPEND
> +	 flag was specified, we_wordc and we_wordv shall not be modified.
> +
> +	 Free strings appended during this call, discard the working copy of
> +	 we_wordv, and restore the caller's original pointer.  */
> +      while (pwordexp->we_wordc > old_word.we_wordc)
> +	free (pwordexp->we_wordv[pwordexp->we_offs + --pwordexp->we_wordc]);
> +      free (pwordexp->we_wordv);
> +      pwordexp->we_wordv = saved_wordv;
> +    }
> +  else
> +    {
> +      wordfree (pwordexp);
> +      *pwordexp = old_word;
> +    }
>  
> -  *pwordexp = old_word;
>    return error;
>  }
  

Ping.

On 18/05/26 13:32, Adhemerval Zanella Netto wrote:
> Ping.
> 
> On 22/04/26 09:24, Adhemerval Zanella wrote:
>> The previous implementation saved a copy of the wordexp_t struct at
>> entry and blindly restored it on error via (*pwordexp = old_word).
>> This is incorrect when WRDE_APPEND is set because w_addword may have
>> called realloc on we_wordv during partial processing before the error
>> was detected.  If realloc relocated the buffer, the saved we_wordv
>> pointer is dangling; restoring it causes a use-after-free in the
>> caller (e.g. via wordfree), and the relocated buffer is leaked.
>>
>> Fix this by duplicating the we_wordv pointer array at entry when
>> WRDE_APPEND is set, so that all subsequent realloc calls inside
>> w_addword operate on the copy.
>>
>> This change also fixes a POSIX conformance issue: if the WRDE_APPEND
>> flag is specified, pwordexp->we_wordc and pwordexp->we_wordv shall
>> not be modified.
>>
>> Also fix two pre-existing error return paths in the '"' and '\'' cases
>> that returned directly from w_addword failures instead of going through
>> do_error, which would leak the saved array (and previously would also
>> skip the word cleanup).
>>
>> A new test (tst-wordexp-append) exercises the changes:
>>
>> - we_wordc and we_wordv pointer preserved on WRDE_BADCHAR/WRDE_SYNTAX
>> - we_wordv pointer stability when realloc relocates the buffer
>> - original words remain accessible after a failed append
>> - successful append still works (regression)
>> - recovery: successful append after a failed one
>> - repeated failures do not corrupt the state
>> - error without WRDE_APPEND still cleans up properly
>> - WRDE_BADCHAR on the first character (no partial w_addword)
>> - WRDE_APPEND into an empty (zeroed) wordexp_t
>>
>> Checked on x86_64-linux-gnu and i686-linux-gnu.
>> ---
>>  posix/Makefile             |   1 +
>>  posix/tst-wordexp-append.c | 307 +++++++++++++++++++++++++++++++++++++
>>  posix/wordexp.c            |  64 +++++++-
>>  3 files changed, 364 insertions(+), 8 deletions(-)
>>  create mode 100644 posix/tst-wordexp-append.c
>>
>> diff --git a/posix/Makefile b/posix/Makefile
>> index a5e5162c61..1ee73b0b65 100644
>> --- a/posix/Makefile
>> +++ b/posix/Makefile
>> @@ -329,6 +329,7 @@ tests := \
>>    tst-wait3 \
>>    tst-wait4 \
>>    tst-waitid \
>> +  tst-wordexp-append \
>>    tst-wordexp-nocmd \
>>    tst-wordexp-reuse \
>>    tstgetopt \
>> diff --git a/posix/tst-wordexp-append.c b/posix/tst-wordexp-append.c
>> new file mode 100644
>> index 0000000000..6253520c57
>> --- /dev/null
>> +++ b/posix/tst-wordexp-append.c
>> @@ -0,0 +1,307 @@
>> +/* Test for wordexp with WRDE_APPEND flag.
>> +   Copyright (C) 2026 Free Software Foundation, Inc.
>> +   This file is part of the GNU C Library.
>> +
>> +   The GNU C Library is free software; you can redistribute it and/or
>> +   modify it under the terms of the GNU Lesser General Public
>> +   License as published by the Free Software Foundation; either
>> +   version 2.1 of the License, or (at your option) any later version.
>> +
>> +   The GNU C Library is distributed in the hope that it will be useful,
>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> +   Lesser General Public License for more details.
>> +
>> +   You should have received a copy of the GNU Lesser General Public
>> +   License along with the GNU C Library; if not, see
>> +   <https://www.gnu.org/licenses/>.  */
>> +
>> +#include <wordexp.h>
>> +#include <string.h>
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +
>> +#include <support/check.h>
>> +#include <support/support.h>
>> +
>> +/* Attempt to force realloc to relocate the we_wordv buffer by placing an
>> +   allocation right after it.  Returns a pointer that must be freed after
>> +   the test.  */
>> +static void *
>> +place_blocker (void)
>> +{
>> +  void *p = xmalloc (0x1000);
>> +  /* Write to it so the compiler cannot optimize it away and the allocator
>> +     actually commits the pages.  */
>> +  memset (p, 0x41, 0x1000);
>> +  return p;
>> +}
>> +
>> +/* Verify that all words in we match the expected NULL-terminated
>> +   array.  */
>> +static void
>> +check_words (const wordexp_t *we, const char *const *expected, int line)
>> +{
>> +  size_t i;
>> +  for (i = 0; expected[i] != NULL; i++)
>> +    {
>> +      TEST_VERIFY (i < we->we_wordc);
>> +      TEST_COMPARE_STRING (we->we_wordv[we->we_offs + i], expected[i]);
>> +    }
>> +  TEST_COMPARE (we->we_wordc, i);
>> +}
>> +
>> +#define CHECK_WORDS(we, ...) \
>> +  do {								\
>> +    const char *const expected_[] = { __VA_ARGS__, NULL };	\
>> +    check_words (we, expected_, __LINE__);			\
>> +  } while (0)
>> +
>> +/* Test 1: WRDE_APPEND + WRDE_BADCHAR preserves we_wordc.  */
>> +static void
>> +test_append_badchar_preserves_count (void)
>> +{
>> +  printf ("info: test_append_badchar_preserves_count\n");
>> +  wordexp_t we = { 0 };
>> +
>> +  TEST_COMPARE (wordexp ("one two three", &we, 0), 0);
>> +  TEST_COMPARE (we.we_wordc, 3);
>> +
>> +  size_t saved_count = we.we_wordc;
>> +
>> +  /* ')' triggers WRDE_BADCHAR and  "extra" would be a new word if the
>> +     expansion succeeded, exercising the w_addword path before the error
>> +     is detected.  */
>> +  TEST_COMPARE (wordexp ("extra )", &we, WRDE_APPEND), WRDE_BADCHAR);
>> +  TEST_COMPARE (we.we_wordc, saved_count);
>> +
>> +  wordfree (&we);
>> +}
>> +
>> +/* Test 2: WRDE_APPEND + WRDE_BADCHAR preserves the we_wordv pointer even
>> +   when internal realloc would move the buffer.  */
>> +static void
>> +test_append_badchar_preserves_pointer (void)
>> +{
>> +  printf ("info: test_append_badchar_preserves_pointer\n");
>> +  wordexp_t we = { 0 };
>> +
>> +  /* Use many words so that the initial we_wordv allocation is
>> +     non-trivial and a later realloc is more likely to move it.  */
>> +  TEST_COMPARE (wordexp ("a b c d e f g h", &we, 0), 0);
>> +  TEST_COMPARE (we.we_wordc, 8);
>> +
>> +  char **saved_wordv = we.we_wordv;
>> +  size_t saved_count = we.we_wordc;
>> +
>> +  /* Place an allocation right after to make realloc move the buffer.  */
>> +  void *blocker = place_blocker ();
>> +
>> +  TEST_COMPARE (wordexp ("append )", &we, WRDE_APPEND), WRDE_BADCHAR);
>> +  TEST_COMPARE (we.we_wordc, saved_count);
>> +  TEST_VERIFY (we.we_wordv == saved_wordv);
>> +
>> +  free (blocker);
>> +  wordfree (&we);
>> +}
>> +
>> +/* Test 3: After a failed WRDE_APPEND the original words are still accessible
>> +   and correct.  */
>> +static void
>> +test_append_badchar_words_intact (void)
>> +{
>> +  printf ("info: test_append_badchar_words_intact\n");
>> +  wordexp_t we = { 0 };
>> +
>> +  TEST_COMPARE (wordexp ("alpha beta gamma", &we, 0), 0);
>> +  CHECK_WORDS (&we, "alpha", "beta", "gamma");
>> +
>> +  void *blocker = place_blocker ();
>> +  TEST_COMPARE (wordexp ("delta )", &we, WRDE_APPEND), WRDE_BADCHAR);
>> +  free (blocker);
>> +
>> +  /* Words must still be intact.  */
>> +  CHECK_WORDS (&we, "alpha", "beta", "gamma");
>> +  /* The NULL terminator must still be present.  */
>> +  TEST_VERIFY (we.we_wordv[we.we_offs + we.we_wordc] == NULL);
>> +
>> +  wordfree (&we);
>> +}
>> +
>> +/* Test 4: Successful WRDE_APPEND still works (regression test).  */
>> +static void
>> +test_append_success (void)
>> +{
>> +  printf ("info: test_append_success\n");
>> +  wordexp_t we = { 0 };
>> +
>> +  TEST_COMPARE (wordexp ("hello", &we, 0), 0);
>> +  TEST_COMPARE (we.we_wordc, 1);
>> +
>> +  TEST_COMPARE (wordexp ("world", &we, WRDE_APPEND), 0);
>> +  TEST_COMPARE (we.we_wordc, 2);
>> +  CHECK_WORDS (&we, "hello", "world");
>> +
>> +  wordfree (&we);
>> +}
>> +
>> +/* Test 5: Successful append after a failed append — the implementation must
>> +   recover and allow further use of the wordexp_t.  */
>> +static void
>> +test_append_success_after_failure (void)
>> +{
>> +  printf ("info: test_append_success_after_failure\n");
>> +  wordexp_t we = { 0 };
>> +
>> +  TEST_COMPARE (wordexp ("first", &we, 0), 0);
>> +  CHECK_WORDS (&we, "first");
>> +
>> +  void *blocker = place_blocker ();
>> +  TEST_COMPARE (wordexp ("bad |", &we, WRDE_APPEND), WRDE_BADCHAR);
>> +  free (blocker);
>> +
>> +  /* State must be exactly as before the failed call.  */
>> +  CHECK_WORDS (&we, "first");
>> +
>> +  /* A subsequent successful append must work.  */
>> +  TEST_COMPARE (wordexp ("second third", &we, WRDE_APPEND), 0);
>> +  CHECK_WORDS (&we, "first", "second", "third");
>> +
>> +  wordfree (&we);
>> +}
>> +
>> +/* Test 6: Multiple consecutive failed appends do not corrupt state.  */
>> +static void
>> +test_append_multiple_failures (void)
>> +{
>> +  printf ("info: test_append_multiple_failures\n");
>> +  wordexp_t we = { 0 };
>> +
>> +  TEST_COMPARE (wordexp ("keep this", &we, 0), 0);
>> +  CHECK_WORDS (&we, "keep", "this");
>> +
>> +  size_t saved_count = we.we_wordc;
>> +  char **saved_wordv = we.we_wordv;
>> +
>> +  void *blocker = place_blocker ();
>> +
>> +  /* Each of these bad characters must leave the state unchanged.  */
>> +  TEST_COMPARE (wordexp ("x )", &we, WRDE_APPEND), WRDE_BADCHAR);
>> +  TEST_COMPARE (wordexp ("x |", &we, WRDE_APPEND), WRDE_BADCHAR);
>> +  TEST_COMPARE (wordexp ("x ;", &we, WRDE_APPEND), WRDE_BADCHAR);
>> +  TEST_COMPARE (wordexp ("x &", &we, WRDE_APPEND), WRDE_BADCHAR);
>> +  TEST_COMPARE (wordexp ("x <", &we, WRDE_APPEND), WRDE_BADCHAR);
>> +  TEST_COMPARE (wordexp ("x >", &we, WRDE_APPEND), WRDE_BADCHAR);
>> +
>> +  free (blocker);
>> +
>> +  TEST_COMPARE (we.we_wordc, saved_count);
>> +  TEST_VERIFY (we.we_wordv == saved_wordv);
>> +  CHECK_WORDS (&we, "keep", "this");
>> +
>> +  wordfree (&we);
>> +}
>> +
>> +/* Test 7: WRDE_APPEND with WRDE_SYNTAX error (unterminated quote) also
>> +   preserves state.  */
>> +static void
>> +test_append_syntax_error (void)
>> +{
>> +  printf ("info: test_append_syntax_error\n");
>> +  wordexp_t we = { 0 };
>> +
>> +  TEST_COMPARE (wordexp ("original", &we, 0), 0);
>> +  CHECK_WORDS (&we, "original");
>> +
>> +  char **saved_wordv = we.we_wordv;
>> +  size_t saved_count = we.we_wordc;
>> +
>> +  void *blocker = place_blocker ();
>> +  /* Unterminated double quote triggers WRDE_SYNTAX.  */
>> +  TEST_COMPARE (wordexp ("\"unterminated", &we, WRDE_APPEND), WRDE_SYNTAX);
>> +  free (blocker);
>> +
>> +  TEST_COMPARE (we.we_wordc, saved_count);
>> +  TEST_VERIFY (we.we_wordv == saved_wordv);
>> +  CHECK_WORDS (&we, "original");
>> +
>> +  wordfree (&we);
>> +}
>> +
>> +/* Test 8: Error without WRDE_APPEND still works (regression test for the
>> +   non-APPEND code path in do_error).  */
>> +static void
>> +test_no_append_error (void)
>> +{
>> +  printf ("info: test_no_append_error\n");
>> +  wordexp_t we = { 0 };
>> +
>> +  /* Simple failure without WRDE_APPEND.  */
>> +  TEST_COMPARE (wordexp ("bad |", &we, 0), WRDE_BADCHAR);
>> +
>> +  /* After failure without WRDE_APPEND the struct should be safe to
>> +     reuse — start fresh.  */
>> +  TEST_COMPARE (wordexp ("ok", &we, 0), 0);
>> +  CHECK_WORDS (&we, "ok");
>> +
>> +  wordfree (&we);
>> +}
>> +
>> +/* Test 9: WRDE_BADCHAR on the very first character (no partial words added
>> +   before the error).  */
>> +static void
>> +test_append_badchar_immediate (void)
>> +{
>> +  printf ("info: test_append_badchar_immediate\n");
>> +  wordexp_t we = { 0 };
>> +
>> +  TEST_COMPARE (wordexp ("hello world", &we, 0), 0);
>> +  CHECK_WORDS (&we, "hello", "world");
>> +
>> +  char **saved_wordv = we.we_wordv;
>> +  size_t saved_count = we.we_wordc;
>> +
>> +  /* The bad character is the very first byte — no w_addword call happens
>> +     before the error.  */
>> +  TEST_COMPARE (wordexp ("|", &we, WRDE_APPEND), WRDE_BADCHAR);
>> +  TEST_COMPARE (we.we_wordc, saved_count);
>> +  TEST_VERIFY (we.we_wordv == saved_wordv);
>> +
>> +  wordfree (&we);
>> +}
>> +
>> +/* Test 10: WRDE_APPEND into an empty wordexp_t (initial call uses WRDE_APPEND
>> +   with a zeroed struct — unusual but allowed).  */
>> +static void
>> +test_append_into_empty (void)
>> +{
>> +  printf ("info: test_append_into_empty\n");
>> +  wordexp_t we = { 0 };
>> +
>> +  /* First call with WRDE_APPEND on a zeroed struct.  The implementation
>> +     must handle we_wordv == NULL gracefully.  */
>> +  TEST_COMPARE (wordexp ("solo", &we, WRDE_APPEND), 0);
>> +  TEST_COMPARE (we.we_wordc, 1);
>> +  CHECK_WORDS (&we, "solo");
>> +
>> +  wordfree (&we);
>> +}
>> +
>> +static int
>> +do_test (void)
>> +{
>> +  test_append_badchar_preserves_count ();
>> +  test_append_badchar_preserves_pointer ();
>> +  test_append_badchar_words_intact ();
>> +  test_append_success ();
>> +  test_append_success_after_failure ();
>> +  test_append_multiple_failures ();
>> +  test_append_syntax_error ();
>> +  test_no_append_error ();
>> +  test_append_badchar_immediate ();
>> +  test_append_into_empty ();
>> +
>> +  return 0;
>> +}
>> +
>> +#include <support/test-driver.c>
>> diff --git a/posix/wordexp.c b/posix/wordexp.c
>> index 4a8541add4..119ce05d9c 100644
>> --- a/posix/wordexp.c
>> +++ b/posix/wordexp.c
>> @@ -35,6 +35,7 @@
>>  #include <scratch_buffer.h>
>>  #include <_itoa.h>
>>  #include <assert.h>
>> +#include <intprops.h>
>>  
>>  /*
>>   * This is a recursive-descent-style word expansion routine.
>> @@ -2212,6 +2213,12 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags)
>>    char ifs_white[4];
>>    wordexp_t old_word = *pwordexp;
>>  
>> +  /* When WRDE_APPEND is set we work on a copy of the we_wordv array so that
>> +     the caller's original pointer is never invalidated by realloc inside
>> +     w_addword.  The saved_wordv keeps the original; on success we free it,
>> +     on non-NOSPACE error we free the working copy and restore the original.  */
>> +  char **saved_wordv = NULL;
>> +
>>    if (flags & WRDE_REUSE)
>>      {
>>        /* Minimal implementation of WRDE_REUSE for now */
>> @@ -2246,6 +2253,23 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags)
>>  	  pwordexp->we_offs = 0;
>>  	}
>>      }
>> +  else if (pwordexp->we_wordv != NULL)
>> +    {
>> +      /* WRDE_APPEND with an existing word list: duplicate the array so that
>> +	 realloc during parsing does not invalidate the caller's pointer.  The
>> +	 strings themselves are shared.  */
>> +      size_t num_p;
>> +      char **dup;
>> +      if (INT_ADD_WRAPV (pwordexp->we_offs, pwordexp->we_wordc, &num_p)
>> +	  || INT_ADD_WRAPV (num_p, 1, &num_p))
>> +	return WRDE_NOSPACE;
>> +      dup = __libc_reallocarray (NULL, num_p, sizeof *dup);
>> +      if (dup == NULL)
>> +	return WRDE_NOSPACE;
>> +      memcpy (dup, pwordexp->we_wordv, num_p * sizeof *dup);
>> +      saved_wordv = pwordexp->we_wordv;
>> +      pwordexp->we_wordv = dup;
>> +    }
>>  
>>    /* Find out what the field separators are.
>>     * There are two types: whitespace and non-whitespace.
>> @@ -2326,7 +2350,7 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags)
>>  	    error = w_addword (pwordexp, NULL);
>>  
>>  	    if (error)
>> -	      return error;
>> +	      goto do_error;
>>  	  }
>>  
>>  	break;
>> @@ -2344,7 +2368,7 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags)
>>  	    error = w_addword (pwordexp, NULL);
>>  
>>  	    if (error)
>> -	      return error;
>> +	      goto do_error;
>>  	  }
>>  
>>  	break;
>> @@ -2410,10 +2434,15 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags)
>>  
>>    /* There was a word separator at the end */
>>    if (word == NULL) /* i.e. w_newword */
>> -    return 0;
>> +    {
>> +      free (saved_wordv);
>> +      return 0;
>> +    }
>>  
>>    /* There was no field separator at the end */
>> -  return w_addword (pwordexp, word);
>> +  error = w_addword (pwordexp, word);
>> +  free (saved_wordv);
>> +  return error;
>>  
>>  do_error:
>>    /* Error:
>> @@ -2424,11 +2453,30 @@ do_error:
>>    free (word);
>>  
>>    if (error == WRDE_NOSPACE)
>> -    return WRDE_NOSPACE;
>> +    {
>> +      /* we_wordc and we_wordv are updated to reflect any words that were
>> +	 successfully expanded.  The old array is obsolete.  */
>> +      free (saved_wordv);
>> +      return WRDE_NOSPACE;
>> +    }
>>  
>> -  if ((flags & WRDE_APPEND) == 0)
>> -    wordfree (pwordexp);
>> +  if (flags & WRDE_APPEND)
>> +    {
>> +      /* POSIX 2024 states that for in other error cases, if the WRDE_APPEND
>> +	 flag was specified, we_wordc and we_wordv shall not be modified.
>> +
>> +	 Free strings appended during this call, discard the working copy of
>> +	 we_wordv, and restore the caller's original pointer.  */
>> +      while (pwordexp->we_wordc > old_word.we_wordc)
>> +	free (pwordexp->we_wordv[pwordexp->we_offs + --pwordexp->we_wordc]);
>> +      free (pwordexp->we_wordv);
>> +      pwordexp->we_wordv = saved_wordv;
>> +    }
>> +  else
>> +    {
>> +      wordfree (pwordexp);
>> +      *pwordexp = old_word;
>> +    }
>>  
>> -  *pwordexp = old_word;
>>    return error;
>>  }
>
  

* Adhemerval Zanella:

> diff --git a/posix/tst-wordexp-append.c b/posix/tst-wordexp-append.c
> new file mode 100644
> index 0000000000..6253520c57
> --- /dev/null
> +++ b/posix/tst-wordexp-append.c
> @@ -0,0 +1,307 @@

> +/* Attempt to force realloc to relocate the we_wordv buffer by placing an
> +   allocation right after it.  Returns a pointer that must be freed after
> +   the test.  */
> +static void *
> +place_blocker (void)
> +{
> +  void *p = xmalloc (0x1000);
> +  /* Write to it so the compiler cannot optimize it away and the allocator
> +     actually commits the pages.  */
> +  memset (p, 0x41, 0x1000);
> +  return p;
> +}

Is it possible to replace this with an interposed realloc?  Wouldn't
that result in a much more predictable test?

None of the tests check interaction with WRDE_DOOFFS.

The actual code changes look okay to me.

Thanks,
Florian
  

On 01/07/26 10:18, Florian Weimer wrote:
> * Adhemerval Zanella:
> 
>> diff --git a/posix/tst-wordexp-append.c b/posix/tst-wordexp-append.c
>> new file mode 100644
>> index 0000000000..6253520c57
>> --- /dev/null
>> +++ b/posix/tst-wordexp-append.c
>> @@ -0,0 +1,307 @@
> 
>> +/* Attempt to force realloc to relocate the we_wordv buffer by placing an
>> +   allocation right after it.  Returns a pointer that must be freed after
>> +   the test.  */
>> +static void *
>> +place_blocker (void)
>> +{
>> +  void *p = xmalloc (0x1000);
>> +  /* Write to it so the compiler cannot optimize it away and the allocator
>> +     actually commits the pages.  */
>> +  memset (p, 0x41, 0x1000);
>> +  return p;
>> +}
> 
> Is it possible to replace this with an interposed realloc?  Wouldn't
> that result in a much more predictable test?

A interposed realloc would be better indeed to reproduce it, I use this to
follow the initial POC from the reporter. I will change to use it instead.

> 
> None of the tests check interaction with WRDE_DOOFFS.

Fair, I will add them as well.

> 
> The actual code changes look okay to me.
> 
> Thanks,
> Florian
>