commit-graph.c: handle commit parsing errors

To write a commit graph chunk, 'write_graph_chunk_data()' takes a list
of commits to write and parses each one before writing the necessary
data, and continuing on to the next commit in the list.

Since the majority of these commits are not parsed ahead of time (an
exception is made for the *last* commit in the list, which is parsed
early within 'copy_oids_to_commits'), it is possible that calling
'parse_commit_no_graph()' on them may return an error. Failing to catch
these errors before de-referencing later calls can result in a undefined
memory access and a SIGSEGV.

One such example of this is 'get_commit_tree_oid()', which expects a
parsed object as its input (in this case, the commit-graph code passes
'*list'). If '*list' causes a parse error, the subsequent call will
fail.

Prevent such an issue by checking the return value of
'parse_commit_no_graph()' to avoid passing an unparsed object to a
function which expects a parsed object, thus preventing a segfault.

It is worth noting that this fix is really skirting around the issue in
object.c's 'parse_object()', which makes it difficult to tell how
corrupt an object is without digging into it. Presumably one could
change the meaning of 'parse_object' returns, but this would require
adjusting each callsite accordingly. Instead of that, add an additional
check to the object parsed.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/commit-graph.c b/commit-graph.c
index f2888c203b677a8a0091f7f63129efe282899172..6aa6998ecd3aa6aa02aa51811c5e9314f75c8879 100644 (file)
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -843,7 +843,9 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
                uint32_t packedDate[2];
                display_progress(ctx->progress, ++ctx->progress_cnt);
 
-               parse_commit_no_graph(*list);
+               if (parse_commit_no_graph(*list))
+                       die(_("unable to parse commit %s"),
+                               oid_to_hex(&(*list)->object.oid));
                hashwrite(f, get_commit_tree_oid(*list)->hash, hash_len);
 
                parent = (*list)->parents;

diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index c855f819302dc991853244ee65a053b92eee964e..abde8d4e900a360a7390d797235a4958c95a6c2e 100755 (executable)
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -585,7 +585,7 @@ test_expect_success 'get_commit_tree_in_graph works for non-the_repository' '
        test_cmp expect actual
 '
 
-test_expect_failure 'corrupt commit-graph write (broken parent)' '
+test_expect_success 'corrupt commit-graph write (broken parent)' '
        rm -rf repo &&
        git init repo &&
        (