[PATCH] posix: Fix wordexp WRDE_APPEND to preserve state on non-NOSPACE errors (BZ 34090, CVE-2026-6368)
Adhemerval Zanella Netto
adhemerval.zanella@linaro.org
Mon May 18 16:32:02 GMT 2026
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;
> }
More information about the Libc-alpha
mailing list