fsck: correctly compute checksums on idx files larger than 4GB

peff · gitster · commit 33bbc59fed34 · 2020-11-16T13:41:35.000-08:00
When checking the trailing checksum hash of a .idx file, we pass the whole buffer (minus the trailing hash) into a single call to the_hash_algo->update_fn(). But we cast it to an "unsigned int". This comes from c4001d9 (Use off_t when we really mean a file offset., 2007-03-06). That commit started storing the index_size variable as an off_t, but our mozilla-sha1 implementation from the time was limited to a smaller size. Presumably the cast was a way of annotating that we expected .idx files to be small, and so we didn't need to loop (as we do for arbitrarily-large .pack files). Though as an aside it was still wrong, because the mozilla function actually took a signed int. These days our hash-update functions are defined to take a size_t, so we can pass the whole buffer in directly. The cast is actually causing a buggy truncation! While we're here, though, let's drop the confusing off_t variable in the first place. We're getting the size not from the filesystem anyway, but from p->index_size, which is a size_t. In fact, we can make the code a bit more readable by dropping our local variable duplicating p->index_size, and instead have one that stores the size of the actual index data, minus the trailing hash. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/pack-check.c b/pack-check.c
@@ -164,22 +164,22 @@ static int verify_packfile(struct repository *r,
 
 int verify_pack_index(struct packed_git *p)
 {
-	off_t index_size;
+	size_t len;
 	const unsigned char *index_base;
 	git_hash_ctx ctx;
 	unsigned char hash[GIT_MAX_RAWSZ];
 	int err = 0;
 
 	if (open_pack_index(p))
 		return error("packfile %s index not opened", p->pack_name);
-	index_size = p->index_size;
 	index_base = p->index_data;
+	len = p->index_size - the_hash_algo->rawsz;
 
 	/* Verify SHA1 sum of the index file */
 	the_hash_algo->init_fn(&ctx);
-	the_hash_algo->update_fn(&ctx, index_base, (unsigned int)(index_size - the_hash_algo->rawsz));
+	the_hash_algo->update_fn(&ctx, index_base, len);
 	the_hash_algo->final_fn(hash, &ctx);
-	if (!hasheq(hash, index_base + index_size - the_hash_algo->rawsz))
+	if (!hasheq(hash, index_base + len))
 		err = error("Packfile index for %s hash mismatch",
 			    p->pack_name);
 	return err;
