On 211205 1917, Konstantin Khlebnikov wrote: > Fuzzer is supposed to stop when first bug is found and report failure. > Present fuzzers fork new child at each iteration to isolate side-effects. > But child's exit code is ignored, i.e. libfuzzer does not see any crashes. > > Right now virtio-net fuzzer instantly falls on assert in iov_copy and > dumps crash-*, but fuzzing continues and ends successfully if global > timeout is set. > > Let's put required logic into helper function "fork_fuzzer_and_wait". >
Hi Konstantin, Can you provide more details about them problem this is meant to solve? Currently, the fuzzer would just output a "crash-" file and continue fuzzing. So the crash isn't lost - it can still be reproduced later. This means the fuzzer can progress faster (no need to restart the whole process each time there is a crash). However, this is of course, not the default libfuzzer behavior. That's why I wonder whether you encountered some issue that depended on libfuzzer exiting immediately. We have had some problems on OSS-Fuzz, with incomplete coverage reports, and I wonder if this could be related. For the example you gave, OSS-Fuzz picked up on the crash, so even though we don't comform to the default libfuzzer behavior, the crashes are still detected. https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=23985&q=iov_copy&can=2 Small question below. > Signed-off-by: Konstantin Khlebnikov <khlebni...@yandex-team.ru> > --- > tests/qtest/fuzz/fork_fuzz.c | 26 ++++++++++++++++++++++++++ > tests/qtest/fuzz/fork_fuzz.h | 1 + > tests/qtest/fuzz/generic_fuzz.c | 3 +-- > tests/qtest/fuzz/i440fx_fuzz.c | 3 +-- > tests/qtest/fuzz/virtio_blk_fuzz.c | 6 ++---- > tests/qtest/fuzz/virtio_net_fuzz.c | 6 ++---- > tests/qtest/fuzz/virtio_scsi_fuzz.c | 6 ++---- > 7 files changed, 35 insertions(+), 16 deletions(-) > > diff --git a/tests/qtest/fuzz/fork_fuzz.c b/tests/qtest/fuzz/fork_fuzz.c > index 6ffb2a7937..6e3a3867bf 100644 > --- a/tests/qtest/fuzz/fork_fuzz.c > +++ b/tests/qtest/fuzz/fork_fuzz.c > @@ -38,4 +38,30 @@ void counter_shm_init(void) > free(copy); > } > > +/* Returns true in child process */ > +bool fork_fuzzer_and_wait(void) > +{ > + pid_t pid; > + int wstatus; > + > + pid = fork(); > + if (pid < 0) { > + perror("fork"); > + abort(); > + } > + > + if (pid == 0) { > + return true; > + } > > + if (waitpid(pid, &wstatus, 0) < 0) { > + perror("waitpid"); > + abort(); > + } > + > + if (!WIFEXITED(wstatus) || WEXITSTATUS(wstatus) != 0) { > + abort(); > + } Maybe instead of these aborts, we return "true" so the fork-server tries to run the input, itself and (hopefully) crashes. That way we would have an accurate stack trace, instead of abort, which is probably important for the OSS-Fuzz crash-bucketing. Thanks -Alex > + > + return false; > +} > diff --git a/tests/qtest/fuzz/fork_fuzz.h b/tests/qtest/fuzz/fork_fuzz.h > index 9ecb8b58ef..792e922731 100644 > --- a/tests/qtest/fuzz/fork_fuzz.h > +++ b/tests/qtest/fuzz/fork_fuzz.h > @@ -18,6 +18,7 @@ extern uint8_t __FUZZ_COUNTERS_START; > extern uint8_t __FUZZ_COUNTERS_END; > > void counter_shm_init(void); > +bool fork_fuzzer_and_wait(void); > > #endif > > diff --git a/tests/qtest/fuzz/generic_fuzz.c b/tests/qtest/fuzz/generic_fuzz.c > index dd7e25851c..f0e25b39ea 100644 > --- a/tests/qtest/fuzz/generic_fuzz.c > +++ b/tests/qtest/fuzz/generic_fuzz.c > @@ -667,7 +667,7 @@ static void generic_fuzz(QTestState *s, const unsigned > char *Data, size_t Size) > size_t cmd_len; > uint8_t op; > > - if (fork() == 0) { > + if (fork_fuzzer_and_wait()) { > struct sigaction sact; > struct itimerval timer; > sigset_t set; > @@ -723,7 +723,6 @@ static void generic_fuzz(QTestState *s, const unsigned > char *Data, size_t Size) > _Exit(0); > } else { > flush_events(s); > - wait(0); > } > } > > diff --git a/tests/qtest/fuzz/i440fx_fuzz.c b/tests/qtest/fuzz/i440fx_fuzz.c > index 86796bff2b..0b927f4b3a 100644 > --- a/tests/qtest/fuzz/i440fx_fuzz.c > +++ b/tests/qtest/fuzz/i440fx_fuzz.c > @@ -147,12 +147,11 @@ static void i440fx_fuzz_qos(QTestState *s, > > static void i440fx_fuzz_qos_fork(QTestState *s, > const unsigned char *Data, size_t Size) { > - if (fork() == 0) { > + if (fork_fuzzer_and_wait()) { > i440fx_fuzz_qos(s, Data, Size); > _Exit(0); > } else { > flush_events(s); > - wait(NULL); > } > } > > diff --git a/tests/qtest/fuzz/virtio_blk_fuzz.c > b/tests/qtest/fuzz/virtio_blk_fuzz.c > index 623a756fd4..9532dc1fa7 100644 > --- a/tests/qtest/fuzz/virtio_blk_fuzz.c > +++ b/tests/qtest/fuzz/virtio_blk_fuzz.c > @@ -136,13 +136,12 @@ static void virtio_blk_fork_fuzz(QTestState *s, > if (!queues) { > queues = qvirtio_blk_init(blk->vdev, 0); > } > - if (fork() == 0) { > + if (fork_fuzzer_and_wait()) { > virtio_blk_fuzz(s, queues, Data, Size); > flush_events(s); > _Exit(0); > } else { > flush_events(s); > - wait(NULL); > } > } > > @@ -152,7 +151,7 @@ static void virtio_blk_with_flag_fuzz(QTestState *s, > QVirtioBlk *blk = fuzz_qos_obj; > static QVirtioBlkQueues *queues; > > - if (fork() == 0) { > + if (fork_fuzzer_and_wait()) { > if (Size >= sizeof(uint64_t)) { > queues = qvirtio_blk_init(blk->vdev, *(uint64_t *)Data); > virtio_blk_fuzz(s, queues, > @@ -162,7 +161,6 @@ static void virtio_blk_with_flag_fuzz(QTestState *s, > _Exit(0); > } else { > flush_events(s); > - wait(NULL); > } > } > > diff --git a/tests/qtest/fuzz/virtio_net_fuzz.c > b/tests/qtest/fuzz/virtio_net_fuzz.c > index 0e873ab8e2..6b492ef9e7 100644 > --- a/tests/qtest/fuzz/virtio_net_fuzz.c > +++ b/tests/qtest/fuzz/virtio_net_fuzz.c > @@ -118,26 +118,24 @@ static void virtio_net_fuzz_multi(QTestState *s, > static void virtio_net_fork_fuzz(QTestState *s, > const unsigned char *Data, size_t Size) > { > - if (fork() == 0) { > + if (fork_fuzzer_and_wait()) { > virtio_net_fuzz_multi(s, Data, Size, false); > flush_events(s); > _Exit(0); > } else { > flush_events(s); > - wait(NULL); > } > } > > static void virtio_net_fork_fuzz_check_used(QTestState *s, > const unsigned char *Data, size_t Size) > { > - if (fork() == 0) { > + if (fork_fuzzer_and_wait()) { > virtio_net_fuzz_multi(s, Data, Size, true); > flush_events(s); > _Exit(0); > } else { > flush_events(s); > - wait(NULL); > } > } > > diff --git a/tests/qtest/fuzz/virtio_scsi_fuzz.c > b/tests/qtest/fuzz/virtio_scsi_fuzz.c > index 6ff6fabe4a..c7eaf3242b 100644 > --- a/tests/qtest/fuzz/virtio_scsi_fuzz.c > +++ b/tests/qtest/fuzz/virtio_scsi_fuzz.c > @@ -140,13 +140,12 @@ static void virtio_scsi_fork_fuzz(QTestState *s, > if (!queues) { > queues = qvirtio_scsi_init(scsi->vdev, 0); > } > - if (fork() == 0) { > + if (fork_fuzzer_and_wait()) { > virtio_scsi_fuzz(s, queues, Data, Size); > flush_events(s); > _Exit(0); > } else { > flush_events(s); > - wait(NULL); > } > } > > @@ -156,7 +155,7 @@ static void virtio_scsi_with_flag_fuzz(QTestState *s, > QVirtioSCSI *scsi = fuzz_qos_obj; > static QVirtioSCSIQueues *queues; > > - if (fork() == 0) { > + if (fork_fuzzer_and_wait()) { > if (Size >= sizeof(uint64_t)) { > queues = qvirtio_scsi_init(scsi->vdev, *(uint64_t *)Data); > virtio_scsi_fuzz(s, queues, > @@ -166,7 +165,6 @@ static void virtio_scsi_with_flag_fuzz(QTestState *s, > _Exit(0); > } else { > flush_events(s); > - wait(NULL); > } > } > >