In packfile.c:1680, there's an infinite loop that tries to get
to the base of a packfile. With offset deltas, the offset needs
to be greater than 0, so it's always walking backwards, and the
search is guaranteed to terminate.
With reference deltas, there's no check for a cycle in the
references, so a cyclic reference will cause git to loop
infinitely, growing the delta_stack infinitely, which will
cause it to consume all available memory as as a full CPU
core.
This change puts an arbitrary limit of 10,000 on the number
of iterations we make when chasing down a base commit, to
prevent looping forever, using all available memory growing
the delta stack.
---
packfile.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/packfile.c b/packfile.c
index 6ab5233613..321e002c50 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1633,6 +1633,7 @@ static void write_pack_access_log(struct packed_git *p, off_t obj_offset)
int do_check_packed_object_crc;
+#define UNPACK_ENTRY_STACK_LIMIT 10000
#define UNPACK_ENTRY_STACK_PREALLOC 64
struct unpack_entry_stack_ent {
off_t obj_offset;
@@ -1715,6 +1716,12 @@ void *unpack_entry(struct repository *r, struct packed_git *p, off_t obj_offset,
break;
}
+ if (delta_stack_nr > UNPACK_ENTRY_STACK_LIMIT) {
+ error("overlong delta chain at offset %jd from %s",
+ (uintmax_t)curpos, p->pack_name);
+ goto out;
+ }
+
/* push object, proceed to base */
if (delta_stack_nr >= delta_stack_alloc
&& delta_stack == small_delta_stack) {
--
2.27.0
