stdio-common: Handle -1 buffer size in __sprintf_chk & co (bug 30039)
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Description |
dj/TryBot-apply_patch |
success
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Patch applied to master at the time it was sent
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dj/TryBot-32bit |
success
|
Build for i686
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Commit Message
This shows up as an assertion failure when sprintf is called with
a specifier like "%.8g" and libquadmath is linked in:
Fatal glibc error: printf_buffer_as_file.c:31
(__printf_buffer_as_file_commit): assertion failed:
file->stream._IO_write_ptr <= file->next->write_end
Fix this by detecting pointer wraparound in __vsprintf_internal
and saturate the addition to the end of the address space instead.
Tested on i686-linux-gnu, x86_64-linux-gnu. Proposed as a release
blocker.
---
debug/Makefile | 5 ++
debug/tst-sprintf-fortify-unchecked.c | 126 ++++++++++++++++++++++++++++++++++
include/printf_buffer.h | 19 +++--
libio/iovsprintf.c | 15 ++--
4 files changed, 155 insertions(+), 10 deletions(-)
base-commit: 103a469dc7755fd9e8ccf362f3dd4c55dc761908
Comments
On 1/24/23 06:31, Florian Weimer via Libc-alpha wrote:
> This shows up as an assertion failure when sprintf is called with
> a specifier like "%.8g" and libquadmath is linked in:
>
> Fatal glibc error: printf_buffer_as_file.c:31
> (__printf_buffer_as_file_commit): assertion failed:
> file->stream._IO_write_ptr <= file->next->write_end
>
> Fix this by detecting pointer wraparound in __vsprintf_internal
> and saturate the addition to the end of the address space instead.
>
> Tested on i686-linux-gnu, x86_64-linux-gnu. Proposed as a release
> blocker.
OK for immediate commit to master for 2.37 release.
Thanks for looking into this and resolving it so quickly.
The testing coverage looks good too, particularly both paths.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>
> ---
> debug/Makefile | 5 ++
> debug/tst-sprintf-fortify-unchecked.c | 126 ++++++++++++++++++++++++++++++++++
> include/printf_buffer.h | 19 +++--
> libio/iovsprintf.c | 15 ++--
> 4 files changed, 155 insertions(+), 10 deletions(-)
>
> diff --git a/debug/Makefile b/debug/Makefile
> index 13f15d15d3..52f9a7852c 100644
> --- a/debug/Makefile
> +++ b/debug/Makefile
> @@ -200,6 +200,10 @@ LDFLAGS-tst-backtrace6 = -rdynamic
>
> CFLAGS-tst-ssp-1.c += -fstack-protector-all
>
> +# Disable compiler optimizations around vsprintf (the function under test).
> +CFLAGS-tst-sprintf-fortify-unchecked.c = \
> + -fno-builtin-vsprintf -fno-builtin-__vsprintf_chk
OK. First use of these for any test in glibc. Though we use the heavier hammer of -fno-builtin
in several other tests.
> +
> tests = backtrace-tst \
> tst-longjmp_chk \
> test-strcpy_chk \
> @@ -211,6 +215,7 @@ tests = backtrace-tst \
> tst-backtrace5 \
> tst-backtrace6 \
> tst-realpath-chk \
> + tst-sprintf-fortify-unchecked \
OK. In alapha order? Yes.
> $(tests-all-chk)
>
> tests-time64 += \
> diff --git a/debug/tst-sprintf-fortify-unchecked.c b/debug/tst-sprintf-fortify-unchecked.c
> new file mode 100644
> index 0000000000..7c7bd1b5e4
> --- /dev/null
> +++ b/debug/tst-sprintf-fortify-unchecked.c
> @@ -0,0 +1,126 @@
> +/* Tests for fortified sprintf with unknown buffer bounds (bug 30039).
OK. 30039.
> + Copyright (C) 2023 Free Software Foundation, Inc.
OK. Right year.
> + 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 <printf.h>
> +#include <stdarg.h>
> +#include <stdio.h>
> +#include <string.h>
> +#include <support/check.h>
> +
> +/* This test is not built with _FORTIFY_SOURCE. Instead it calls the
> + appropriate implementation directly. The fortify mode is specified
> + in this variable. */
> +static int fortify_mode;
OK.
> +
> +/* This does not handle long-double redirects etc., but we test only
> + format strings that stay within the confines of the base
> + implementation. */
> +int __vsprintf_chk (char *s, int flag, size_t slen, const char *format,
> + va_list ap);
OK.
> +
> +/* Invoke vsprintf or __vsprintf_chk according to fortify_mode. */
> +static int
> +my_vsprintf (char *buf, const char *format, va_list ap)
> +{
> + int result;
> + if (fortify_mode == 0)
> + result = vsprintf (buf, format, ap);
OK.
> + else
> + /* Call the fortified version with an unspecified length. */
> + result = __vsprintf_chk (buf, fortify_mode - 1, -1, format, ap);
OK. Args are: buffer, flag, size, format, va_list. We are consciously passing
size of -1, and a 0 value for fortify_mode == 1, otherwise >1, which has an
impact on PRINTF_FORTIFY being put in mode.
> + return result;
> +}
> +
> +/* Run one test, with the specified expected output. */
> +static void __attribute ((format (printf, 2, 3)))
> +do_check (const char *expected, const char *format, ...)
> +{
> + va_list ap;
> + va_start (ap, format);
> +
> + char buf_expected[24];
OK. Largest test with XXX string has 23 chars and a NULL, so 24, and then
later TEST_VERIFY asserted.
> + memset (buf_expected, '@', sizeof (buf_expected));
> + TEST_VERIFY (strlen (expected) < sizeof (buf_expected));
> + strcpy (buf_expected, expected);
> +
> + char buf[sizeof (buf_expected)];
> + memset (buf, '@', sizeof (buf));
> +
> + int ret = my_vsprintf (buf, format, ap);
> + TEST_COMPARE_BLOB (buf_expected, sizeof (buf_expected), buf, sizeof (buf));
OK. Compare the expected and output buffers.
> + TEST_COMPARE (ret, strlen (expected));
OK. Likewise the expected return results.
> +
> + va_end (ap);
> +}
> +
> +/* Run the tests in all fortify modes. */
> +static void
> +do_tests (void)
> +{
> + for (fortify_mode = 0; fortify_mode <= 3; ++fortify_mode)
OK.
fortify_mode = 0, no _chk call, just sanity case.
fortify_mode = 1, call _chk, PRINTF_CHK set, PRINTF_FORTIFY not set.
fortify_mode = 2, call _chk, PRINTF_CHK set, PRINTF_FORTIFY set.
fortify_mode = 3, same as 2 (in the current impl).
> + {
> + do_check ("0", "%d", 0);
> + do_check ("-2147483648", "%d", -2147483647 - 1);
> + do_check ("-9223372036854775808", "%lld", -9223372036854775807LL - 1);
> + do_check ("", "%s", "");
> + do_check (" ", "%22s", "");
> + do_check ("XXXXXXXXXXXXXXXXXXXXXX", "%s", "XXXXXXXXXXXXXXXXXXXXXX");
> + do_check ("1.125000", "%f", 1.125);
> + do_check ("1.125", "%g", 1.125);
> + do_check ("1.125", "%.8g", 1.125);
> + }
> +}
> +
> +/* printf callback that falls back to the glibc-supplied
> + implementation. */
> +static int
> +dummy_printf_function (FILE *__stream,
> + const struct printf_info *__info,
> + const void *const *__args)
> +{
> + return -2; /* Request fallback. */
OK. Magic -2 return instructs printf_positional to fall back to JUMP
call to handle spec.
> +}
> +
> +/* Likewise for the type information. */
> +static int
> +dummy_arginfo_function (const struct printf_info *info,
> + size_t n, int *argtypes, int *size)
> +{
> + return -1; /* Request fallback. */
OK. Magic < 0 return instructs __parse_one_specmb to fall back to normal
specifiers.
> +}
> +
> +static int
> +do_test (void)
> +{
> + do_tests ();
> +
> + /* Activate __printf_function_invoke mode. */
> + register_printf_specifier ('d', dummy_printf_function,
> + dummy_arginfo_function);
> + register_printf_specifier ('g', dummy_printf_function,
> + dummy_arginfo_function);
> + register_printf_specifier ('s', dummy_printf_function,
> + dummy_arginfo_function);
OK. Xprintf_buffer will fall back to the slow do_positional version if these
functions are present. This tests the functionality of both parts of vfprintf.
> +
> + /* Rerun the tests with callback functions. */
> + do_tests ();
> +
> + return 0;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/include/printf_buffer.h b/include/printf_buffer.h
> index 55feebf279..4d787e4b2c 100644
> --- a/include/printf_buffer.h
> +++ b/include/printf_buffer.h
> @@ -115,17 +115,26 @@ __printf_buffer_has_failed (struct __printf_buffer *buf)
> return buf->mode == __printf_buffer_mode_failed;
> }
>
> +/* Initialization of a buffer, using the memory region from [BASE,
> + END) as the initial buffer contents. */
> +static inline void
> +__printf_buffer_init_end (struct __printf_buffer *buf, char *base, char *end,
> + enum __printf_buffer_mode mode)
> +{
> + buf->write_base = base;
> + buf->write_ptr = base;
> + buf->write_end = end;
> + buf->written = 0;
> + buf->mode = mode;
> +}
OK. Helper (uses base and end, maybe without length being known).
> +
> /* Initialization of a buffer, using the memory region from [BASE, BASE +LEN)
> as the initial buffer contents. LEN can be zero. */
> static inline void
> __printf_buffer_init (struct __printf_buffer *buf, char *base, size_t len,
> enum __printf_buffer_mode mode)
> {
> - buf->write_base = base;
> - buf->write_ptr = base;
> - buf->write_end = base + len;
> - buf->written = 0;
> - buf->mode = mode;
> + __printf_buffer_init_end (buf, base, base + len, mode);
OK. Refactor (length known).
> }
>
> /* Called by printf_buffer_putc for a full buffer. */
> diff --git a/libio/iovsprintf.c b/libio/iovsprintf.c
> index 8d53e401cc..9a4f59a06e 100644
> --- a/libio/iovsprintf.c
> +++ b/libio/iovsprintf.c
> @@ -45,14 +45,19 @@ __vsprintf_internal (char *string, size_t maxlen,
> if ((mode_flags & PRINTF_CHK) != 0)
> {
> string[0] = '\0';
> - __printf_buffer_init (&buf, string, maxlen,
> + /* In some cases, __sprintf_chk is called with an unknown buffer
> + size (the special value -1). Prevent pointer wraparound in
> + this case and saturate to the end of the address space. */
> + uintptr_t end;
> + if (__builtin_add_overflow ((uintptr_t) string, maxlen, &end))
> + end = -1;
OK. Compute string + maxlen and store in &end, but if we overflow then set end to -1.
This is the core fix for 30039.
Other uses of __printf_buffer_init that might need fixing?
* libio/vsnprintf.c - Could suffer from the same overflow?
- Yes, but the user provides the size.
* libio/iovdprintf.c - No fix needed, since the known size is used.
* libio/obprintf.c - Likewise.
* libio/vasprintf.c - Likewise.
* stdio-common/printf_fphex.c - Likewise.
* stdio-common/printf_fp.c - Likewise.
* stdio-common/printf_buffer_to_file.c - Likewise.
* stdlib/strfmon_l.c - Likewise.
> + __printf_buffer_init_end (&buf, string, (char *) end,
OK, use the new __printf_buffer_init_end helper.
> __printf_buffer_mode_sprintf_chk);
> }
> else
> - {
> - __printf_buffer_init (&buf, string, 0, __printf_buffer_mode_sprintf);
> - buf.write_end = (char *) ~(uintptr_t) 0; /* End of address space. */
> - }
> + /* Use end of address space. */
> + __printf_buffer_init_end (&buf, string, (char *) ~(uintptr_t) 0,
> + __printf_buffer_mode_sprintf);
OK. Refactored helper allows cleaning this up.
>
> __printf_buffer (&buf, format, args, mode_flags);
>
>
> base-commit: 103a469dc7755fd9e8ccf362f3dd4c55dc761908
>
@@ -200,6 +200,10 @@ LDFLAGS-tst-backtrace6 = -rdynamic
CFLAGS-tst-ssp-1.c += -fstack-protector-all
+# Disable compiler optimizations around vsprintf (the function under test).
+CFLAGS-tst-sprintf-fortify-unchecked.c = \
+ -fno-builtin-vsprintf -fno-builtin-__vsprintf_chk
+
tests = backtrace-tst \
tst-longjmp_chk \
test-strcpy_chk \
@@ -211,6 +215,7 @@ tests = backtrace-tst \
tst-backtrace5 \
tst-backtrace6 \
tst-realpath-chk \
+ tst-sprintf-fortify-unchecked \
$(tests-all-chk)
tests-time64 += \
new file mode 100644
@@ -0,0 +1,126 @@
+/* Tests for fortified sprintf with unknown buffer bounds (bug 30039).
+ Copyright (C) 2023 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 <printf.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+#include <support/check.h>
+
+/* This test is not built with _FORTIFY_SOURCE. Instead it calls the
+ appropriate implementation directly. The fortify mode is specified
+ in this variable. */
+static int fortify_mode;
+
+/* This does not handle long-double redirects etc., but we test only
+ format strings that stay within the confines of the base
+ implementation. */
+int __vsprintf_chk (char *s, int flag, size_t slen, const char *format,
+ va_list ap);
+
+/* Invoke vsprintf or __vsprintf_chk according to fortify_mode. */
+static int
+my_vsprintf (char *buf, const char *format, va_list ap)
+{
+ int result;
+ if (fortify_mode == 0)
+ result = vsprintf (buf, format, ap);
+ else
+ /* Call the fortified version with an unspecified length. */
+ result = __vsprintf_chk (buf, fortify_mode - 1, -1, format, ap);
+ return result;
+}
+
+/* Run one test, with the specified expected output. */
+static void __attribute ((format (printf, 2, 3)))
+do_check (const char *expected, const char *format, ...)
+{
+ va_list ap;
+ va_start (ap, format);
+
+ char buf_expected[24];
+ memset (buf_expected, '@', sizeof (buf_expected));
+ TEST_VERIFY (strlen (expected) < sizeof (buf_expected));
+ strcpy (buf_expected, expected);
+
+ char buf[sizeof (buf_expected)];
+ memset (buf, '@', sizeof (buf));
+
+ int ret = my_vsprintf (buf, format, ap);
+ TEST_COMPARE_BLOB (buf_expected, sizeof (buf_expected), buf, sizeof (buf));
+ TEST_COMPARE (ret, strlen (expected));
+
+ va_end (ap);
+}
+
+/* Run the tests in all fortify modes. */
+static void
+do_tests (void)
+{
+ for (fortify_mode = 0; fortify_mode <= 3; ++fortify_mode)
+ {
+ do_check ("0", "%d", 0);
+ do_check ("-2147483648", "%d", -2147483647 - 1);
+ do_check ("-9223372036854775808", "%lld", -9223372036854775807LL - 1);
+ do_check ("", "%s", "");
+ do_check (" ", "%22s", "");
+ do_check ("XXXXXXXXXXXXXXXXXXXXXX", "%s", "XXXXXXXXXXXXXXXXXXXXXX");
+ do_check ("1.125000", "%f", 1.125);
+ do_check ("1.125", "%g", 1.125);
+ do_check ("1.125", "%.8g", 1.125);
+ }
+}
+
+/* printf callback that falls back to the glibc-supplied
+ implementation. */
+static int
+dummy_printf_function (FILE *__stream,
+ const struct printf_info *__info,
+ const void *const *__args)
+{
+ return -2; /* Request fallback. */
+}
+
+/* Likewise for the type information. */
+static int
+dummy_arginfo_function (const struct printf_info *info,
+ size_t n, int *argtypes, int *size)
+{
+ return -1; /* Request fallback. */
+}
+
+static int
+do_test (void)
+{
+ do_tests ();
+
+ /* Activate __printf_function_invoke mode. */
+ register_printf_specifier ('d', dummy_printf_function,
+ dummy_arginfo_function);
+ register_printf_specifier ('g', dummy_printf_function,
+ dummy_arginfo_function);
+ register_printf_specifier ('s', dummy_printf_function,
+ dummy_arginfo_function);
+
+ /* Rerun the tests with callback functions. */
+ do_tests ();
+
+ return 0;
+}
+
+#include <support/test-driver.c>
@@ -115,17 +115,26 @@ __printf_buffer_has_failed (struct __printf_buffer *buf)
return buf->mode == __printf_buffer_mode_failed;
}
+/* Initialization of a buffer, using the memory region from [BASE,
+ END) as the initial buffer contents. */
+static inline void
+__printf_buffer_init_end (struct __printf_buffer *buf, char *base, char *end,
+ enum __printf_buffer_mode mode)
+{
+ buf->write_base = base;
+ buf->write_ptr = base;
+ buf->write_end = end;
+ buf->written = 0;
+ buf->mode = mode;
+}
+
/* Initialization of a buffer, using the memory region from [BASE, BASE +LEN)
as the initial buffer contents. LEN can be zero. */
static inline void
__printf_buffer_init (struct __printf_buffer *buf, char *base, size_t len,
enum __printf_buffer_mode mode)
{
- buf->write_base = base;
- buf->write_ptr = base;
- buf->write_end = base + len;
- buf->written = 0;
- buf->mode = mode;
+ __printf_buffer_init_end (buf, base, base + len, mode);
}
/* Called by printf_buffer_putc for a full buffer. */
@@ -45,14 +45,19 @@ __vsprintf_internal (char *string, size_t maxlen,
if ((mode_flags & PRINTF_CHK) != 0)
{
string[0] = '\0';
- __printf_buffer_init (&buf, string, maxlen,
+ /* In some cases, __sprintf_chk is called with an unknown buffer
+ size (the special value -1). Prevent pointer wraparound in
+ this case and saturate to the end of the address space. */
+ uintptr_t end;
+ if (__builtin_add_overflow ((uintptr_t) string, maxlen, &end))
+ end = -1;
+ __printf_buffer_init_end (&buf, string, (char *) end,
__printf_buffer_mode_sprintf_chk);
}
else
- {
- __printf_buffer_init (&buf, string, 0, __printf_buffer_mode_sprintf);
- buf.write_end = (char *) ~(uintptr_t) 0; /* End of address space. */
- }
+ /* Use end of address space. */
+ __printf_buffer_init_end (&buf, string, (char *) ~(uintptr_t) 0,
+ __printf_buffer_mode_sprintf);
__printf_buffer (&buf, format, args, mode_flags);