[PATCH v2] posix: Avoid a stack overflow when glob is given many trailing slashes [BZ #30635]

[Collin Funk]

* posix/glob.c (__glob): Strip trailing slashes before the recursive
call, so it is not called for every trailing slash in the pattern.
* posix/tst-glob-bz30635.c: Add a test case that would previously
segmentation fault.
* posix/Makefile (tests): Add the new test.
---
 posix/Makefile           |  1 +
 posix/glob.c             |  4 ++++
 posix/tst-glob-bz30635.c | 46 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 51 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..82ee873d80 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];
+               dirname < p && 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..f51b1b7e49
--- /dev/null
+++ b/posix/tst-glob-bz30635.c
@@ -0,0 +1,46 @@
+/* Test that glob does not overflow the stack with many trailing 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);
+  memset (pattern, '/', SIZE - 1);
+  pattern[SIZE - 1] = '\0';
+  TEST_VERIFY (glob (pattern, 0, NULL, &g) == 0);
+  globfree (&g);
+  return 0;
+}
+
+#include <support/test-driver.c>
-- 
2.51.0