fuzz-commit-graph identified a case where Git will read past the end of
a buffer containing a commit graph if the graph's header has an
incorrect chunk count. A simple bounds check in parse_commit_graph()
prevents this.
Signed-off-by: Josh Steadmon <steadmon@xxxxxxxxxx>
---
commit-graph.c | 14 ++++++++++++--
t/t5318-commit-graph.sh | 16 +++++++++++++---
2 files changed, 25 insertions(+), 5 deletions(-)
diff --git a/commit-graph.c b/commit-graph.c
index 07dd410f3c..836d65a1d3 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -165,10 +165,20 @@ struct commit_graph *parse_commit_graph(void *graph_map, int fd,
last_chunk_offset = 8;
chunk_lookup = data + 8;
for (i = 0; i < graph->num_chunks; i++) {
- uint32_t chunk_id = get_be32(chunk_lookup + 0);
- uint64_t chunk_offset = get_be64(chunk_lookup + 4);
+ uint32_t chunk_id;
+ uint64_t chunk_offset;
int chunk_repeated = 0;
+ if (data + graph_size - chunk_lookup <
+ GRAPH_CHUNKLOOKUP_WIDTH) {
+ error(_("chunk lookup table entry missing; graph file may be incomplete"));
+ free(graph);
+ return NULL;
+ }
+
+ chunk_id = get_be32(chunk_lookup + 0);
+ chunk_offset = get_be64(chunk_lookup + 4);
+
chunk_lookup += GRAPH_CHUNKLOOKUP_WIDTH;
if (chunk_offset > graph_size - GIT_MAX_RAWSZ) {
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 5fe21db99f..694f26079f 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -366,9 +366,10 @@ GRAPH_OCTOPUS_DATA_OFFSET=$(($GRAPH_COMMIT_DATA_OFFSET + \
GRAPH_BYTE_OCTOPUS=$(($GRAPH_OCTOPUS_DATA_OFFSET + 4))
GRAPH_BYTE_FOOTER=$(($GRAPH_OCTOPUS_DATA_OFFSET + 4 * $NUM_OCTOPUS_EDGES))
-# usage: corrupt_graph_and_verify <position> <data> <string>
+# usage: corrupt_graph_and_verify <position> <data> <string> [<zero_pos>]
# Manipulates the commit-graph file at the position
-# by inserting the data, then runs 'git commit-graph verify'
+# by inserting the data, optionally zeroing the file
+# starting at <zero_pos>, then runs 'git commit-graph verify'
# and places the output in the file 'err'. Test 'err' for
# the given string.
corrupt_graph_and_verify() {
@@ -376,11 +377,15 @@ corrupt_graph_and_verify() {
data="${2:-\0}"
grepstr=$3
cd "$TRASH_DIRECTORY/full" &&
+ orig_size=$(wc -c < $objdir/info/commit-graph) &&
+ zero_pos=${4:-${orig_size}} &&
test_when_finished mv commit-graph-backup $objdir/info/commit-graph &&
cp $objdir/info/commit-graph commit-graph-backup &&
printf "$data" | dd of="$objdir/info/commit-graph" bs=1 seek="$pos" conv=notrunc &&
+ dd of="$objdir/info/commit-graph" bs=1 seek="$zero_pos" count=0 &&
+ dd if=/dev/zero of="$objdir/info/commit-graph" bs=1 seek="$zero_pos" count=$(($orig_size - $zero_pos)) &&
test_must_fail git commit-graph verify 2>test_err &&
- grep -v "^+" test_err >err
+ grep -v "^+" test_err >err &&
test_i18ngrep "$grepstr" err
}
@@ -484,6 +489,11 @@ test_expect_success 'detect invalid checksum hash' '
"incorrect checksum"
'
+test_expect_success 'detect incorrect chunk count' '
+ corrupt_graph_and_verify $GRAPH_BYTE_CHUNK_COUNT "\377" \
+ "chunk lookup table entry missing" $GRAPH_CHUNK_LOOKUP_OFFSET
+'
+
test_expect_success 'git fsck (checks commit-graph)' '
cd "$TRASH_DIRECTORY/full" &&
git fsck &&
--
2.20.1.97.g81188d93c3-goog
