[PATCH v2] string: strerror must not return NULL (bug 30555)

[Arjun Shankar]

> For strerror, this fixes commit 28aff047818eb1726394296d27b ("string:
> Implement strerror in terms of strerror_l").  This commit avoids
> returning NULL for strerror_l as well, although POSIX allows this
> behavior for strerror_l.

This looks good to me.
Reviewed-by: Arjun Shankar <arjun@redhat.com>

>
> ---
> v2: Change wording of comment as suggested by Andreas.
>  string/Makefile            |  1 +
>  string/strerror_l.c        | 13 +++++---
>  string/tst-strerror-fail.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 87 insertions(+), 4 deletions(-)
>
> diff --git a/string/Makefile b/string/Makefile
> index 0ad276cc6a..d3106d10a9 100644
> --- a/string/Makefile
> +++ b/string/Makefile
> @@ -178,6 +178,7 @@ tests := \
>    tst-endian \
>    tst-inlcall \
>    tst-memmove-overflow \
> +  tst-strerror-fail \
>    tst-strfry \
>    tst-strlcat \
>    tst-strlcpy \

OK. Add new test to Makefile.

> diff --git a/string/strerror_l.c b/string/strerror_l.c
> index 7fe9b1d903..e5c8666198 100644
> --- a/string/strerror_l.c
> +++ b/string/strerror_l.c

We want to:
1. Try to return "Unknown error NNN" with the error number included.
2. If that fails, simply return "Unknown error" and not NULL.

> @@ -43,10 +43,15 @@ __strerror_l (int errnum, locale_t loc)
>        struct tls_internal_t *tls_internal = __glibc_tls_internal ();
>        free (tls_internal->strerror_l_buf);

Buffer freed here unconditionally.

>        if (__asprintf (&tls_internal->strerror_l_buf, "%s%d",
> -                     translate ("Unknown error ", loc), errnum) == -1)
> -       tls_internal->strerror_l_buf = NULL;
> -
> -      err = tls_internal->strerror_l_buf;

Earlier, if asprintf failed, we set the thread local buffer pointer to
NULL and eventually returned that.

Now:

> +                     translate ("Unknown error ", loc), errnum) > 0)

OK. We consider any negative or 0 return value (i.e. 0 bytes printed)
from asprintf as error, which is safer than just considering -1 as an
error.

> +       err = tls_internal->strerror_l_buf;

OK. Success case comes first with the negated condition above.

> +      else
> +       {
> +         /* The memory was freed above.  */
> +         tls_internal->strerror_l_buf = NULL;

OK. Yes, we did just free the buffer, so we set it to NULL.

> +         /* Provide a fallback translation.  */
> +         err = (char *) translate ("Unknown error", loc);
> +       }

OK. We give up trying to return "Unknown error NNN" and simply
return "Unknown error" instead.

>      }
>    else
>      err = (char *) translate (err, loc);
> diff --git a/string/tst-strerror-fail.c b/string/tst-strerror-fail.c
> new file mode 100644
> index 0000000000..e0fa45ab2b
> --- /dev/null
> +++ b/string/tst-strerror-fail.c
> @@ -0,0 +1,77 @@
> +/* Check that strerror, strerror_l do not return NULL on  failure (bug 30555).
> +   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 <locale.h>
> +#include <stdbool.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <support/check.h>
> +#include <support/namespace.h>
> +#include <support/xdlfcn.h>
> +
> +/* Interposed malloc that can be used to inject allocation failures.  */
> +
> +static volatile bool fail_malloc;
> +
> +void *
> +malloc (size_t size)
> +{
> +  if (fail_malloc)
> +    return NULL;
> +
> +  static void *(*original_malloc) (size_t);
> +  if (original_malloc == NULL)
> +    original_malloc = xdlsym (RTLD_NEXT, "malloc");
> +  return original_malloc (size);
> +}

OK.

> +
> +/* Callbacks for the actual tests.  Use fork to run both tests with a
> +   clean state.  */
> +
> +static void
> +test_strerror (void *closure)
> +{
> +  fail_malloc = true;
> +  const char *s = strerror (999);
> +  fail_malloc = false;

OK. Force malloc failure.

> +  TEST_COMPARE_STRING (s, "Unknown error");

OK. Check for the correct string.

> +}
> +
> +static void
> +test_strerror_l (void *closure)
> +{
> +  locale_t loc = newlocale (LC_ALL, "C", (locale_t) 0);
> +  TEST_VERIFY (loc != (locale_t) 0);
> +  fail_malloc = true;
> +  const char *s = strerror_l (999, loc);
> +  fail_malloc = false;
> +  TEST_COMPARE_STRING (s, "Unknown error");
> +  freelocale (loc);
> +}

OK. Same.

> +
> +static int
> +do_test (void)
> +{
> +  support_isolate_in_subprocess (test_strerror, NULL);
> +  support_isolate_in_subprocess (test_strerror_l, NULL);
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>

OK. Both strerror and strerror_l shouldn't return NULL on malloc failure.

>
> base-commit: 388ae538ddcb05c7d8966147b488a5f6e481656e
>


-- 
Arjun Shankar
he/him/his