[PATCH 6/9] check_stream_oid(): discard hash on read error

[Jeff King <peff@peff.net>]

The happy path of check_stream_oid() is to initialize a hash, feed the
loose object zlib stream into it, and then get the final result. But if
we hit a zlib error or see extra cruft we'll bail early with an error.

Since we never call git_hash_final() in this cases, any resources held
by the git_hash_ctx may be leaked. Our default hash algorithms don't
allocate anything in the hash_ctx, but some implementations do. For
example, running:

  make SANITIZE=leak \
       OPENSSL_SHA256=1 \
       GIT_TEST_DEFAULT_HASH=sha256 \
       test

will fail t1450, since it feeds corrupted objects that cause us to bail
from check_stream_oid(). This patch fixes it by discarding the hash in
those early return paths. Trying to jump to a common "out:" label is not
worth it here, as we must _not_ discard a hash that was already fed to
git_hash_final(). And the hash_ctx itself does not carry any information
(so we cannot check for a NULL pointer, etc).

Signed-off-by: Jeff King <peff@peff.net>
---
 object-file.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/object-file.c b/object-file.c
index 32a0d6d237..035d005279 100644
--- a/object-file.c
+++ b/object-file.c
@@ -1587,11 +1587,13 @@ static int check_stream_oid(git_zstream *stream,
 
 	if (status != Z_STREAM_END) {
 		error(_("corrupt loose object '%s'"), oid_to_hex(expected_oid));
+		git_hash_discard(&c);
 		return -1;
 	}
 	if (stream->avail_in) {
 		error(_("garbage at end of loose object '%s'"),
 		      oid_to_hex(expected_oid));
+		git_hash_discard(&c);
 		return -1;
 	}
 
-- 
2.55.0.418.g37da59dd42