Re: [PATCH 1/2] commit-graph, fuzz: Add fuzzer for commit-graph
From: Junio C Hamano <hidden>
Date: 2018-12-06 01:32:22
Josh Steadmon [off-list ref] writes:
quoted hunk
@@ -108,27 +106,61 @@ struct commit_graph *load_commit_graph_one(const char *graph_file) die(_("graph file %s is too small"), graph_file); } graph_map = xmmap(NULL, graph_size, PROT_READ, MAP_PRIVATE, fd, 0); + ret = parse_commit_graph(graph_map, fd, graph_size);
OK, assuming that the new helper returns NULL from all places in the original that would have jumped to the cleanup-fail label, this would do the same thing (it may not be the right thing to exit, but that is OK for the purpose of this change).
+ if (ret == NULL) {
+ munmap(graph_map, graph_size);
+ close(fd);
+ exit(1);
+ }
+
+ return ret;
+}
+
+/*
+ * This function is intended to be used only from load_commit_graph_one() or in
+ * fuzz tests.
+ */Hmph, is that necessary to say? "Right now, it has only these two callers" is sometimes handy for those without good static analysis tools, like "git grep" ;-), but I do not think of a reason why a new caller we'll add in the future, who happens to have the data of the graph file in-core, should not be allowed to call this function.
+struct commit_graph *parse_commit_graph(void *graph_map, int fd,
+ size_t graph_size)
+{
+ const unsigned char *data, *chunk_lookup;
+ uint32_t i;
+ struct commit_graph *graph;
+ uint64_t last_chunk_offset;
+ uint32_t last_chunk_id;
+ uint32_t graph_signature;
+ unsigned char graph_version, hash_version;
+
+ /*
+ * This should already be checked in load_commit_graph_one, but we still
+ * need a check here for when we're calling parse_commit_graph directly
+ * from fuzz tests. We can omit the error message in that case.
+ */In the same spirit, I am dubious of the longer-term value of this comment. As an explanation of why this conversion is correct in the proposed log message for this change, it perfectly makes sense, though.
+ if (graph_size < GRAPH_MIN_SIZE) + return NULL; +
The load_commit_graph_one() grabbed graph_map out of xmmap() so it is guaranteed to be non-NULL, but we need to check graph_map != NULL when we're calling this directly from the fuzz tests, exactly in the same spirit that we check graph_size above. Besides, these are to make sure future callers won't misuse the API.
data = (const unsigned char *)graph_map;
And the reset of the function is the same as the original modulo jumping to the cleanup_fail label has been replaced with returning NULL. Looks good.
quoted hunk
... - -cleanup_fail: - munmap(graph_map, graph_size); - close(fd); - exit(1); } static void prepare_commit_graph_one(struct repository *r, const char *obj_dir)diff --git a/fuzz-commit-graph.c b/fuzz-commit-graph.c new file mode 100644 index 0000000000..420851d0d2 --- /dev/null +++ b/fuzz-commit-graph.c@@ -0,0 +1,18 @@ +#include "object-store.h" +#include "commit-graph.h" + +struct commit_graph *parse_commit_graph(void *graph_map, int fd, + size_t graph_size); + +int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size); + +int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) +{ + struct commit_graph *g; + + g = parse_commit_graph((void *) data, -1, size); + if (g) + free(g); + + return 0; +}