Re: [PATCH 2/3] check_stream_sha1(): handle input underflow

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

> The bug comes from commit f6371f9210 (sha1_file: add
> read_loose_object() function, 2017-01-13), which
> reimplemented some of the existing loose object functions.
> So it's worth checking if this bug was inherited from any of
> those. The answers seems to be no. The two obvious
> candidates are both OK:
>
>   1. unpack_sha1_rest(); this doesn't need to loop on
>      Z_BUF_ERROR at all, since it allocates the expected
>      output buffer in advance (which we can't do since we're
>      explicitly streaming here)
>
>   2. check_object_signature(); the streaming path relies on
>      the istream interface, which uses read_istream_loose()
>      for this case. That function uses a similar "is our
>      output buffer full" check with Z_BUF_ERROR (which is
>      where I stole it from for this patch!)

See 692f0bc7 to find who did the fix you stole from, and for what
kind of breakage the original fix was made.

By the way, a very similar loop for pack_non_delta istream iterates
while total_read is smaller than sz, but it does not have the same
check upon BUF_ERROR to see if we've read everything.