paint_alloc() allocates a big block of memory and splits it into
smaller, fixed size, chunks of memory whenever it's called. Each chunk
contains enough bits to present all "new refs" [1] in a fetch from a
shallow repository.
We do not check if the new "big block" is smaller than the requested
memory chunk though. If it happens, we'll happily pass back a memory
region smaller than expected. Which will lead to problems eventually.
A normal fetch may add/update a dozen new refs. Let's stay on the
"reasonably extreme" side and say we need 16k refs (or bits from
paint_alloc's perspective). Each chunk of memory would be 2k, much
smaller than the memory pool (512k).
So, normally, the under-allocation situation should never happen. A bad
guy, however, could make a fetch that adds more than 4m new/updated refs
to this code which results in a memory chunk larger than pool size.
Check this case and abort.
Noticed-by: Rasmus Villemoes <rv@xxxxxxxxxxxxxxxxxx>
[1] Details are in commit message of 58babff (shallow.c: the 8 steps to
select new commits for .git/shallow - 2013-12-05), step 6.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>
---
shallow.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/shallow.c b/shallow.c
index 2512ed3..75e1702 100644
--- a/shallow.c
+++ b/shallow.c
@@ -447,6 +447,9 @@ static uint32_t *paint_alloc(struct paint_info *info)
unsigned size = nr * sizeof(uint32_t);
void *p;
if (!info->pool_count || info->free + size > info->end) {
+ if (size > POOL_SIZE)
+ die("BUG: pool size too small for %d in paint_alloc()",
+ size);
info->pool_count++;
REALLOC_ARRAY(info->pools, info->pool_count);
info->free = xmalloc(POOL_SIZE);
--
2.8.2.524.g6ff3d78