[v3,2/3] realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX [BZ #28770]
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Commit Message
realpath returns an allocated string when the result exceeds PATH_MAX,
which is unexpected when its second argument is not NULL. This results
in the second argument (resolved) being uninitialized and also results
in a memory leak since the caller expects resolved to be the same as the
returned value.
Return NULL and set errno to ENAMETOOLONG if the result exceeds
PATH_MAX. This fixes [BZ #28770], which is CVE-2021-3998.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
NEWS | 4 +++
stdlib/Makefile | 1 +
stdlib/canonicalize.c | 12 +++++++--
stdlib/tst-realpath-toolong.c | 49 +++++++++++++++++++++++++++++++++++
4 files changed, 64 insertions(+), 2 deletions(-)
create mode 100644 stdlib/tst-realpath-toolong.c
Comments
On Thu, 20 Jan 2022, Siddhesh Poyarekar via Libc-alpha wrote:
> diff --git a/stdlib/tst-realpath-toolong.c b/stdlib/tst-realpath-toolong.c
> + char buf[PATH_MAX + 1];
This has broken the testsuite build for Hurd.
tst-realpath-toolong.c: In function 'do_test':
tst-realpath-toolong.c:37:12: error: 'PATH_MAX' undeclared (first use in this function)
On 22/01/2022 04:52, Joseph Myers wrote:
> On Thu, 20 Jan 2022, Siddhesh Poyarekar via Libc-alpha wrote:
>
>> diff --git a/stdlib/tst-realpath-toolong.c b/stdlib/tst-realpath-toolong.c
>
>> + char buf[PATH_MAX + 1];
>
> This has broken the testsuite build for Hurd.
>
> tst-realpath-toolong.c: In function 'do_test':
> tst-realpath-toolong.c:37:12: error: 'PATH_MAX' undeclared (first use in this function)
>
Sorry I missed that, I'll post a fix. I was getting a different build
error on hurd which prevented me from seeing this. I'm rebuilding my
build-many-glibcs to see if that fixes it.
Thanks,
Siddhesh
On Jan 20 2022, Siddhesh Poyarekar via Libc-alpha wrote:
> diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c
> index f36bdf4c76..732dc7ea46 100644
> --- a/stdlib/canonicalize.c
> +++ b/stdlib/canonicalize.c
> @@ -400,8 +400,16 @@ realpath_stk (const char *name, char *resolved,
>
> error:
> *dest++ = '\0';
> - if (resolved != NULL && dest - rname <= get_path_max ())
> - rname = strcpy (resolved, rname);
> + if (resolved != NULL)
> + {
> + if (dest - rname <= get_path_max ())
> + rname = strcpy (resolved, rname);
> + else
> + {
> + failed = true;
> + __set_errno (ENAMETOOLONG);
> + }
> + }
Shouldn't that preserve any preexisting error? I think the result
should only be copied if !failed.
On 24/01/2022 19:15, Andreas Schwab wrote:
> On Jan 20 2022, Siddhesh Poyarekar via Libc-alpha wrote:
>
>> diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c
>> index f36bdf4c76..732dc7ea46 100644
>> --- a/stdlib/canonicalize.c
>> +++ b/stdlib/canonicalize.c
>> @@ -400,8 +400,16 @@ realpath_stk (const char *name, char *resolved,
>>
>> error:
>> *dest++ = '\0';
>> - if (resolved != NULL && dest - rname <= get_path_max ())
>> - rname = strcpy (resolved, rname);
>> + if (resolved != NULL)
>> + {
>> + if (dest - rname <= get_path_max ())
>> + rname = strcpy (resolved, rname);
>> + else
>> + {
>> + failed = true;
>> + __set_errno (ENAMETOOLONG);
>> + }
>> + }
>
> Shouldn't that preserve any preexisting error?
like this?
diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c
index 732dc7ea46..6caed9e70e 100644
--- a/stdlib/canonicalize.c
+++ b/stdlib/canonicalize.c
@@ -404,7 +404,7 @@ error:
{
if (dest - rname <= get_path_max ())
rname = strcpy (resolved, rname);
- else
+ else if (!failed)
{
failed = true;
__set_errno (ENAMETOOLONG);
> I think the result
> should only be copied if !failed.
>
Looks like tests in test-canon.c depend on buf contents having being
copied in despite failure.
Siddhesh
On Jan 24 2022, Siddhesh Poyarekar wrote:
> Looks like tests in test-canon.c depend on buf contents having being
> copied in despite failure.
That is not supported by POSIX.
On 24/01/2022 20:18, Andreas Schwab wrote:
> On Jan 24 2022, Siddhesh Poyarekar wrote:
>
>> Looks like tests in test-canon.c depend on buf contents having being
>> copied in despite failure.
>
> That is not supported by POSIX.
>
OK, I'll file a separate bug and fix for it then. Is the fix I posted
sufficient for your other concern, i.e. not overriding preexisting error?
Thanks,
Siddhesh
On Jan 24 2022, Siddhesh Poyarekar wrote:
> Is the fix I posted sufficient for your other concern, i.e. not
> overriding preexisting error?
Yes.
@@ -166,6 +166,10 @@ Security related changes:
CVE-2022-23218: Passing an overlong file name to the svcunix_create
legacy function could result in a stack-based buffer overflow.
+ CVE-2021-3998: Passing a path longer than PATH_MAX to the realpath
+ function could result in a memory leak and potential access of
+ uninitialized memory. Reported by Qualys.
+
The following bugs are resolved with this release:
[The release manager will add the list generated by
@@ -109,6 +109,7 @@ tests := \
tst-random \
tst-random2 \
tst-realpath \
+ tst-realpath-toolong \
tst-secure-getenv \
tst-setcontext \
tst-setcontext2 \
@@ -400,8 +400,16 @@ realpath_stk (const char *name, char *resolved,
error:
*dest++ = '\0';
- if (resolved != NULL && dest - rname <= get_path_max ())
- rname = strcpy (resolved, rname);
+ if (resolved != NULL)
+ {
+ if (dest - rname <= get_path_max ())
+ rname = strcpy (resolved, rname);
+ else
+ {
+ failed = true;
+ __set_errno (ENAMETOOLONG);
+ }
+ }
error_nomem:
scratch_buffer_free (&extra_buffer);
new file mode 100644
@@ -0,0 +1,49 @@
+/* Verify that realpath returns NULL with ENAMETOOLONG if the result exceeds
+ NAME_MAX.
+ Copyright The GNU Toolchain Authors.
+ 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 <errno.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <support/check.h>
+#include <support/temp_file.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#define BASENAME "tst-realpath-toolong."
+
+int
+do_test (void)
+{
+ char *base = support_create_and_chdir_toolong_temp_directory (BASENAME);
+
+ char buf[PATH_MAX + 1];
+ const char *res = realpath (".", buf);
+
+ /* canonicalize.c states that if the real path is >= PATH_MAX, then
+ realpath returns NULL and sets ENAMETOOLONG. */
+ TEST_VERIFY (res == NULL);
+ TEST_VERIFY (errno == ENAMETOOLONG);
+
+ free (base);
+ return 0;
+}
+
+#include <support/test-driver.c>