[PATCH v3] posix: Avoid a stack overflow when glob is given many slashes [BZ #30635]

[Adhemerval Zanella Netto]

On 11/10/25 23:01, Collin Funk wrote:
> * posix/glob.c (__glob): Strip trailing slashes before the recursive
> call, so it is not called for every slash in the pattern.
> * posix/tst-glob-bz30635.c: Add two test cases that would previously
> segmentation fault. The first test has many trailing slashes and the
> second has many slashes following a wildcard character.
> * posix/Makefile (tests): Add the new test.

LGTM, thanks.  There is no need to add a ChangeLog entry, but I think
it is up to.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  posix/Makefile           |  1 +
>  posix/glob.c             |  4 +++
>  posix/tst-glob-bz30635.c | 56 ++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 61 insertions(+)
>  create mode 100644 posix/tst-glob-bz30635.c
> 
> diff --git a/posix/Makefile b/posix/Makefile
> index a36e5decd3..f6421e5379 100644
> --- a/posix/Makefile
> +++ b/posix/Makefile
> @@ -288,6 +288,7 @@ tests := \
>    tst-fork \
>    tst-gai_strerror \
>    tst-getopt_long1 \
> +  tst-glob-bz30635 \
>    tst-glob-tilde \
>    tst-glob_symlinks \
>    tst-gnuglob \
> diff --git a/posix/glob.c b/posix/glob.c
> index a7c7dd1ebe..0c86d26972 100644
> --- a/posix/glob.c
> +++ b/posix/glob.c
> @@ -596,6 +596,10 @@ __glob (const char *pattern, int flags, int (*errfunc) (const char *, int),
>                    flags &= ~(GLOB_NOCHECK | GLOB_NOMAGIC);
>                  }
>              }
> +          /* Prevent stack overflows with many trailing '/' characters.  */
> +          for (char *p = &dirname[dirlen - 1];
> +               p > dirname && p[0] == '/' && p[-1] == '/'; --p)
> +            p[0] = '\0';
>            int val = __glob (dirname, flags | GLOB_MARK, errfunc, pglob);
>            if (val == 0)
>              pglob->gl_flags = ((pglob->gl_flags & ~GLOB_MARK)
> diff --git a/posix/tst-glob-bz30635.c b/posix/tst-glob-bz30635.c
> new file mode 100644
> index 0000000000..64e0a977f9
> --- /dev/null
> +++ b/posix/tst-glob-bz30635.c
> @@ -0,0 +1,56 @@
> +/* Test that glob does not overflow the stack with many slashes.
> +   Copyright (C) 2025 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 <glob.h>
> +#include <string.h>
> +#include <support/test-driver.h>
> +#include <support/support.h>
> +#include <support/check.h>
> +#include <sys/resource.h>
> +
> +/* Allocation size.  */
> +#define SIZE 4096
> +
> +/* This test would cause a stack overflow on glibc 2.42 and earlier.  */
> +#define MAX_STACK_SIZE (8 * 1024 * 1024)
> +
> +static int
> +do_test (void)
> +{
> +  struct rlimit stack_limit = { MAX_STACK_SIZE, MAX_STACK_SIZE };
> +  TEST_VERIFY_EXIT (setrlimit (RLIMIT_STACK, &stack_limit) == 0);
> +  glob_t g;
> +  char *pattern = xmalloc (SIZE);
> +
> +  /* Test based on BZ #30635.  "/////////".  */
> +  memset (pattern, '/', SIZE - 1);
> +  pattern[SIZE - 1] = '\0';
> +  TEST_VERIFY (glob (pattern, 0, NULL, &g) == 0);
> +  globfree (&g);
> +
> +  /* Test based on BZ #33537.  "/*/////sh".  */
> +  pattern[1] = '*';
> +  pattern[SIZE - 3] = 's';
> +  pattern[SIZE - 2] = 'h';
> +  TEST_VERIFY (glob (pattern, 0, NULL, &g) == 0);
> +  globfree (&g);
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>