OpenAFS Master Repository branch, master, updated. openafs-devel-1_9_1-274-gf2003ed

[Gerrit Code Review]

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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