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fuzz: do not use POSIX shm for coverage bitmap

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We used shm_open with mmap to share libfuzzer's coverage bitmap with
child (runner) processes. The same functionality can be achieved with
MAP_SHARED | MAP_ANONYMOUS, since we do not care about naming or
permissioning the shared memory object.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Message-Id: <20200622165040.15121-1-alxndr@bu.edu>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
This commit is contained in:
Alexander Bulekov 2020-06-22 12:50:40 -04:00 committed by Thomas Huth
parent 45222b9a90
commit dda2f556c3
1 changed files with 13 additions and 27 deletions
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40
tests/qtest/fuzz/fork_fuzz.c
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@ -17,39 +17,25 @@
void counter_shm_init(void)
{
char *shm_path = g_strdup_printf("/qemu-fuzz-cntrs.%d", getpid());
int fd = shm_open(shm_path, O_CREAT | O_RDWR, S_IRUSR | S_IWUSR);
g_free(shm_path);
if (fd == -1) {
perror("Error: ");
exit(1);
}
if (ftruncate(fd, &__FUZZ_COUNTERS_END - &__FUZZ_COUNTERS_START) == -1) {
perror("Error: ");
exit(1);
}
/* Copy what's in the counter region to the shm.. */
void *rptr = mmap(NULL ,
&__FUZZ_COUNTERS_END - &__FUZZ_COUNTERS_START,
PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
memcpy(rptr,
/* Copy what's in the counter region to a temporary buffer.. */
void *copy = malloc(&__FUZZ_COUNTERS_END - &__FUZZ_COUNTERS_START);
memcpy(copy,
&__FUZZ_COUNTERS_START,
&__FUZZ_COUNTERS_END - &__FUZZ_COUNTERS_START);
munmap(rptr, &__FUZZ_COUNTERS_END - &__FUZZ_COUNTERS_START);
/* And map the shm over the counter region */
rptr = mmap(&__FUZZ_COUNTERS_START,
&__FUZZ_COUNTERS_END - &__FUZZ_COUNTERS_START,
PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED, fd, 0);
close(fd);
if (!rptr) {
/* Map a shared region over the counter region */
if (mmap(&__FUZZ_COUNTERS_START,
&__FUZZ_COUNTERS_END - &__FUZZ_COUNTERS_START,
PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED | MAP_ANONYMOUS,
0, 0) == MAP_FAILED) {
perror("Error: ");
exit(1);
}
/* Copy the original data back to the counter-region */
memcpy(&__FUZZ_COUNTERS_START, copy,
&__FUZZ_COUNTERS_END - &__FUZZ_COUNTERS_START);
free(copy);
}