On 2020.06.05 16:02, Jonathan Nieder wrote:
> Josh Steadmon wrote:
>
> > Use the provided free_commit_graph() to properly free the commit graph
> > in fuzz-commit-graph. Otherwise, the fuzzer itself leaks memory when the
> > struct contains pointers to allocated memory.
> >
> > Signed-off-by: Josh Steadmon <steadmon@xxxxxxxxxx>
> > ---
> > fuzz-commit-graph.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
>
> How can I reproduce this?
Building the fuzzer is dependent on the exact versions of clang &
libFuzzer that you have installed; on my machine, with clang 9.0.1-10
and libFuzzer 9, I build as follows:
$ make CC=clang \
CXX=clang++ \
CFLAGS="-fsanitize=fuzzer-no-link,address" \
LIB_FUZZING_ENGINE=/usr/lib/llvm-9/lib/libFuzzer.a \
fuzz-all
Then you can run fuzz-commit-graph on the attached test case:
$ ./fuzz-commit-graph /tmp/testcase-fuzzer-leak
When built from master, I get a leak error:
$ ./fuzz-commit-graph /tmp/testcase-fuzzer-leak
INFO: Seed: 2332984289
INFO: Loaded 1 modules (70798 inline 8-bit counters): 70798 [0x15c8b82, 0x15da010),
INFO: Loaded 1 PC tables (70798 PCs): 70798 [0x12a7db8,0x13bc698),
./fuzz-commit-graph: Running 1 inputs 1 time(s) each.
Running: /tmp/testcase-5725798091980800
=================================================================
==192153==ERROR: LeakSanitizer: detected memory leaks
Direct leak of 12 byte(s) in 1 object(s) allocated from:
#0 0x49be6d in malloc (/usr/local/google/home/steadmon/src/git/fuzz-commit-graph+0x49be6d)
#1 0xc2ff15 in do_xmalloc (/usr/local/google/home/steadmon/src/git/fuzz-commit-graph+0xc2ff15)
#2 0xc2fe66 in xmalloc (/usr/local/google/home/steadmon/src/git/fuzz-commit-graph+0xc2fe66)
#3 0x5cfc4e in parse_commit_graph (/usr/local/google/home/steadmon/src/git/fuzz-commit-graph+0x5cfc4e)
#4 0x1085b39 in LLVMFuzzerTestOneInput (/usr/local/google/home/steadmon/src/git/fuzz-commit-graph+0x1085b39)
#5 0x109b41c in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) (/usr/local/google/home/steadmon/src/git/fuzz-commit-graph+0x109b41c)
SUMMARY: AddressSanitizer: 12 byte(s) leaked in 1 allocation(s).
INFO: a leak has been found in the initial corpus.
INFO: to ignore leaks on libFuzzer side use -detect_leaks=0.
When run with this patch, the fuzzer does not report a leak.
> > diff --git a/fuzz-commit-graph.c b/fuzz-commit-graph.c
> > index 9fd1c04edd..430817214d 100644
> > --- a/fuzz-commit-graph.c
> > +++ b/fuzz-commit-graph.c
> > @@ -12,7 +12,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
> > initialize_the_repository();
> > g = parse_commit_graph((void *)data, size);
> > repo_clear(the_repository);
> > - free(g);
> > + free_commit_graph(g);
>
> In any event, the patch itself is sensible, so
> Reviewed-by: Jonathan Nieder <jrnieder@xxxxxxxxx>
>
> Thanks.
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