[Bug sanitizer/98920] New: [10/11 Regression] uses regexec without support for REG_STARTEND with -fsanitize=address

["doko at debian dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98920

            Bug ID: 98920
           Summary: [10/11 Regression] uses regexec without support for
                    REG_STARTEND with -fsanitize=address
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: doko at debian dot org
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org, marxin at gcc dot gnu.org
  Target Milestone: ---

[forwarded from https://bugs.debian.org/949192]

When gcc-10 compiles with -fsanitize=address, it substitutes any calls
to regexec with a version that does not support REG_STARTEND.  This
makes code that is compiled fail unexpectedly or even produce spurious
sanitization errors, since with that option the buffer need not be
NUL-terminated.

While REG_STARTEND is not in POSIX, it is found on the BSDs and Linux
and users may reasonably rely on the fact that it is present on those
systems.

This issue has caused a bug in the Git testsuite as seen at
https://lore.kernel.org/git/20200117174931.GA8958@coredump.intra.peff.net/T/#t.

I've attached a testcase.  Without -fsanitize=address, it succeeds
silently.  With -fsanitize=address, it fails and prints an error.

Please either fix the regexec implementation such that it is fully
functional compared to the version in glibc or disable the sanitization
of regexec until it has feature parity.

$ cat test.c 
#include <stdio.h>
#include <sys/types.h>
#include <regex.h>

int main(void)
{
    regex_t r;
    const char s[] = "ban\0ana";
    regmatch_t pmatch[10];
    pmatch[0].rm_so = 0;
    pmatch[0].rm_eo = sizeof(s);
    if (regcomp(&r, "ana", 0))
        return 2;
    if (regexec(&r, s, sizeof(pmatch)/sizeof(pmatch[0]), pmatch, REG_STARTEND))
{
        fprintf(stderr, "failed to match\n");
        regfree(&r);
        return 3;
    }
    regfree(&r);
    return 0;
}


$ gcc-9 -fsanitize=address test.c && ./a.out 

$ gcc-10 -fsanitize=address test.c && ./a.out 
failed to match

$ gcc-11 -fsanitize=address test.c && ./a.out 
failed to match