Re: [PATCH V2 1/2] Fix delta integer overflows

Jeff King [off-list ref] writes:

On Thu, Aug 10, 2017 at 01:07:07PM -0700, Junio C Hamano wrote:

quoted

Perhaps we should teach the receiving end to notice that the varint
data it reads encodes a size that is too large for it to grok and
die.  With that, we can safely move forward with whatever size_t
each platform uses.

Yes, this is very important even for "unsigned long". I'd worry that
malicious input could cause us to wrap to 0, and we'd potentially write
into a too-small buffer[1].

There's some prior art with checking this against bitsizeof() in
unpack_object_header_buffer() but get_delta_hdr_size() does not seem to
have a check.

-Peff

[1] In most cases it's _probably_ not a vulnerability to wrap here,
    because we'd just read less data than we ought to. But it makes me
    nervous nonetheless.

As I said in my other message in the thread, as long as the callers
of get_delta_hdr_size() are written correctly, it should be OK.  And
patch_delta() should be OK, even for "unsigned long" when it is too
small.  It just will not produce correct result and instead abort,
and the patch under discussion fixes that.