OpenAFS Master Repository branch, master, updated. openafs-devel-1_9_1-274-gf2003ed
Gerrit Code Review
gerrit@openafs.org
Wed, 5 Jul 2023 16:41:03 -0400
The following commit has been merged in the master branch:
commit f2003ed68c2fecf679d0b04146427258d39369ea
Author: Cheyenne Wills <cwills@sinenomine.net>
Date: Mon Jul 3 13:14:52 2023 -0600
gcc: Avoid false positive use-after-free in crypto
Due to a bug in gcc-12 and gcc-13, several warnings are generated for a
use-after-free in crypto.c, which leads to a build failure with
--enable-checking:
src/external/heimdal/krb5/crypto.c:1157:9: error: pointer ‘p’ may be
used after ‘realloc’ [-Werror=use-after-free]
1157 | free(p);
| ^~~~~~~
src/external/heimdal/krb5/crypto.c:1155:20: note: call to ‘realloc’
here
1155 | result->data = realloc(p, sz);
| ^~~~~~~~~~~~~~
However, reviewing the code around these warnings shows that the
use-after-free warnings are incorrectly generated (false positive). The
documentation for realloc states that realloc will return a NULL and not
alter the storage passed if there was an error allocating and the size
passed is non-zero.
There is a possible work-around for the false positive. One can use a
variable that is not a member of a structure to hold and test the value
returned from realloc, then update the structure member from that
variable.
However, the code that is producing the message is in a heimdal external
file, so we cannot modify the source. So just use the compiler flag
-Wno-use-after-free to avoid the warning/error.
Update configure to add tests for the -Wno-use-after-free flag, update
the Makefile to add the flag for CFLAGS.crypto.lo, and update CODING
for the new exception.
Because this is an important check, only disable the warning if the
compiler exhibits this specific bug. We do this by adding specific
configure tests for the compiler bug and conditionally set a CFLAG
variable if the bug is present.
NOTE: The false positive and work-around can be demonstrated with the
following code using gcc-12 (with -O0) or gcc-13 (not sensitive to the
optimization level):
somestruct->somepointer = realloc(ptr, somesize);
if (somestruct->somepointer == NULL && somesize != 0) {
free(ptr); << gets flagged as use-after-free
handle enomem...
}
However the following doesn't get flagged:
char *tmpptr = realloc(ptr, somesize);
if (tmpptr == NULL && somesize != 0) {
free(ptr);
handle enomem...
}
somestruct->somepointer = tmpptr;
The GCC ticket https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110501
has been marked as confirmed.
Change-Id: I28566354da4199389964210f954cda1213098088
Reviewed-on: https://gerrit.openafs.org/15471
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
CODING | 2 ++
src/cf/gcc.m4 | 51 ++++++++++++++++++++++++++++++++++++++++++
src/cf/osconf.m4 | 1 +
src/crypto/rfc3961/Makefile.in | 1 +
4 files changed, 55 insertions(+)
--
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