Fix environment traversal when an envvar value is empty

  The condition when the value of an envvar is empty (not just '\0'),
the loop in tunables_init gets stuck infinitely because envp is not
incremented.  Fix that by always incrementing envp in the loop.

Added test case (tst-empty-env.c) verifies the fix when the source is
configured with --enable-hardcoded-path-in-tests, thanks Josh Stone for
providing the test case.  Verified on x86_64.

	* elf/dl-tunables (get_next_env): Always advance envp.
	* stdlib/tst-empty-env.c: New test case.
	* stdlib/Makefile (tests): Use it.
---
 elf/dl-tunables.c      |  4 ++--
 stdlib/Makefile        |  3 +++
 stdlib/tst-empty-env.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+), 2 deletions(-)
 create mode 100644 stdlib/tst-empty-env.c
  

On 01/19/2017 01:42 PM, Siddhesh Poyarekar wrote:
> The condition when the value of an envvar is empty (not just '\0'),
> the loop in tunables_init gets stuck infinitely because envp is not
> incremented.  Fix that by always incrementing envp in the loop.
> 
> Added test case (tst-empty-env.c) verifies the fix when the source is
> configured with --enable-hardcoded-path-in-tests, thanks Josh Stone for
> providing the test case.  Verified on x86_64.
> 
> 	* elf/dl-tunables (get_next_env): Always advance envp.
> 	* stdlib/tst-empty-env.c: New test case.
> 	* stdlib/Makefile (tests): Use it.

Thanks for the fix and test case.

The test needs 2 more comments and it's good to go.

> ---
>  elf/dl-tunables.c      |  4 ++--
>  stdlib/Makefile        |  3 +++
>  stdlib/tst-empty-env.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 55 insertions(+), 2 deletions(-)
>  create mode 100644 stdlib/tst-empty-env.c
> 
> diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
> index e0119d1..ba5246a 100644
> --- a/elf/dl-tunables.c
> +++ b/elf/dl-tunables.c
> @@ -80,7 +80,7 @@ get_next_env (char **envp, char **name, size_t *namelen, char **val)
>  {
>    while (envp != NULL && *envp != NULL)
>      {
> -      char *envline = *envp;
> +      char *envline = *envp++;
>        int len = 0;
>  
>        while (envline[len] != '\0' && envline[len] != '=')
> @@ -94,7 +94,7 @@ get_next_env (char **envp, char **name, size_t *namelen, char **val)
>        *namelen = len;
>        *val = &envline[len + 1];
>  
> -      return ++envp;
> +      return envp;

Looks good.

>      }
>  
>    return NULL;
> diff --git a/stdlib/Makefile b/stdlib/Makefile
> index 0c09973..5751b5d 100644
> --- a/stdlib/Makefile
> +++ b/stdlib/Makefile
> @@ -81,6 +81,9 @@ tests		:= tst-strtol tst-strtod testmb testrand testsort testdiv   \
>  		   tst-quick_exit tst-thread-quick_exit tst-width	    \
>  		   tst-width-stdint tst-strfrom tst-strfrom-locale \
>  		   tst-getrandom
> +ifeq ($(build-hardcoded-path-in-tests),yes)
> +tests += tst-empty-env
> +endif
>  tests-static	:= tst-secure-getenv
>  ifeq ($(have-cxx-thread_local),yes)
>  CFLAGS-tst-quick_exit.o = -std=c++11
> diff --git a/stdlib/tst-empty-env.c b/stdlib/tst-empty-env.c
> new file mode 100644
> index 0000000..48c7f84
> --- /dev/null
> +++ b/stdlib/tst-empty-env.c
> @@ -0,0 +1,50 @@

Need a line with the bug number and what the test does.

> +/* Copyright (C) 2017 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
> +   <http://www.gnu.org/licenses/>.  */
> +
> +/* Sanity test that passing a NULL value for an envvar does not result in any
> +   obscure failures.  The test is useful only when the source is configured
> +   with --enable-hardcoded-path-in-tests since otherwise the execve just picks
> +   up the system dynamic linker.  */
> +
> +#include <stdlib.h>
> +#include <stdio.h>
> +#include <unistd.h>
> +#include <errno.h>
> +
> +static int
> +do_test (int argc, char **argv)
> +{
> +  if (argc == 2)
> +    return 0;
> +
> +  char envname[] = "FOOBAR";
> +  char *filename = program_invocation_name;

Please add a comment referencing the bug and that the environment
must be null and that it hangs and the test will timeout and fail.

> +  char *newargv[] = {filename, filename, NULL};
> +  char *newenviron[] = {envname, NULL};
> +
> +  int ret = execve (filename, newargv, newenviron);
> +
> +  if (ret != 0)
> +    printf ("execve failed: %m");
> +
> +  /* We will reach here only if we fail execve.  */
> +  return 1;
> +}
> +
> +#define TIMEOUT 3
> +#define TEST_FUNCTION_ARGV do_test
> +#include <support/test-driver.c>
>