If parsing a commit yields a valid tree oid, but we've seen that same
oid as a non-tree in the same process, the resulting commit struct will
end up with a NULL tree pointer, but not otherwise report a parsing
failure.
That's perhaps convenient for callers which want to operate on even
partially corrupt commits (e.g., by still looking at the parents). But
it leaves a potential trap for most callers, who now have to manually
check for a NULL tree. Most do not, and it's likely that there are
possible segfaults lurking. I say "possible" because there are many
candidates, and I don't think it's worth following through on
reproducing them when we can just fix them all in one spot. And
certainly we _have_ seen real-world cases, such as the one fixed by
806278dead (commit-graph.c: handle corrupt/missing trees, 2019-09-05).
Note that we can't quite drop the check in the caller added by that
commit yet, as there's some subtlety with repeated parsings (which will
be addressed in a future commit).
Signed-off-by: Jeff King <p...@peff.net>
---
commit.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/commit.c b/commit.c
index 6467c9e175..810419a168 100644
--- a/commit.c
+++ b/commit.c
@@ -401,6 +401,7 @@ int parse_commit_buffer(struct repository *r, struct commit
*item, const void *b
struct commit_graft *graft;
const int tree_entry_len = the_hash_algo->hexsz + 5;
const int parent_entry_len = the_hash_algo->hexsz + 7;
+ struct tree *tree;
if (item->object.parsed)
return 0;
@@ -412,7 +413,12 @@ int parse_commit_buffer(struct repository *r, struct
commit *item, const void *b
if (get_oid_hex(bufptr + 5, &parent) < 0)
return error("bad tree pointer in commit %s",
oid_to_hex(&item->object.oid));
- set_commit_tree(item, lookup_tree(r, &parent));
+ tree = lookup_tree(r, &parent);
+ if (!tree)
+ return error("bad tree pointer %s in commit %s",
+ oid_to_hex(&parent),
+ oid_to_hex(&item->object.oid));
+ set_commit_tree(item, tree);
bufptr += tree_entry_len + 1; /* "tree " + "hex sha1" + "\n" */
pptr = &item->parents;
--
2.23.0.1228.gee29b05929
