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From: Jeff King <>
Subject: [PATCH 3/5] fsck: correctly compute checksums on idx files larger than 4GB
Date: Fri, 13 Nov 2020 00:07:14 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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 c4001d92be (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 <>
 pack-check.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/pack-check.c b/pack-check.c
index db3adf8781..4b089fe8ec 100644
--- 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->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",
 	return err;

  parent reply	other threads:[~2020-11-13  5:07 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-13  5:06 [PATCH 0/5] handling 4GB .idx files Jeff King
2020-11-13  5:06 ` [PATCH 1/5] compute pack .idx byte offsets using size_t Jeff King
2020-11-13  5:07 ` [PATCH 2/5] use size_t to store pack .idx byte offsets Jeff King
2020-11-13  5:07 ` Jeff King [this message]
2020-11-13  5:07 ` [PATCH 4/5] block-sha1: take a size_t length parameter Jeff King
2020-11-13  5:07 ` [PATCH 5/5] packfile: detect overflow in .idx file size checks Jeff King
2020-11-13 11:02   ` Johannes Schindelin
2020-11-15 14:43 ` [PATCH 0/5] handling 4GB .idx files Thomas Braun
2020-11-16  4:10   ` Jeff King
2020-11-16 13:30     ` Derrick Stolee
2020-11-16 23:49       ` Jeff King
2020-11-30 22:57     ` Thomas Braun
2020-12-01 11:23       ` Jeff King
2020-12-01 11:39         ` t7900's new expensive test Jeff King
2020-12-01 20:55           ` Derrick Stolee
2020-12-02  2:47             ` [PATCH] t7900: speed up " Jeff King
2020-12-03 15:23               ` Derrick Stolee
2020-12-01 18:27         ` [PATCH 0/5] handling 4GB .idx files Taylor Blau
2020-12-02 13:12           ` Jeff King

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