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commit-graph: fix buffer read-overflow 

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@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Josh Steadmon 2019-01-15 14:25:51 -08:00 committed by Junio C Hamano
parent aa658574bf
commit d2b86fbaa1
2 changed files with 25 additions and 5 deletions
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14
commit-graph.c
View File

@ -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) {

16
t/t5318-commit-graph.sh
View File

@ -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 &&