Subject: [PATCH 1/2] Skip SHA-1 collision test on "index-pack --verify"

From: Nguyễn Thái Ngọc Duy <[email-masked]>
Date: Fri, 24 Feb 2012 19:23:20 +0700

index-pack --verify (or verify-pack) is about verifying the pack
itself. SHA-1 collision test is about outside (probably malicious)
objects with the same SHA-1 entering current repo.

SHA-1 collision test is currently done unconditionally. Which means if
you verify an in-repo pack, all objects from the pack will be checked
against objects in repo, which are themselves.

Skip this test for --verify, unless --strict is also specified.

linux-2.6 $ ls -sh .git/objects/pack/pack-e7732c98a8d54840add294c3c562840f78764196.pack
401M .git/objects/pack/pack-e7732c98a8d54840add294c3c562840f78764196.pack

Without the patch (and with another patch to cut out second pass in
index-pack):

linux-2.6 $ time ~/w/git/old index-pack -v --verify .git/objects/pack/pack-e7732c98a8d54840add294c3c562840f78764196.pack
Indexing objects: 100% (1944656/1944656), done.
fatal: pack has 1617280 unresolved deltas

real    1m1.223s
user    0m55.028s
sys     0m0.828s

With the patch:

linux-2.6 $ time ~/w/git/git index-pack -v --verify .git/objects/pack/pack-e7732c98a8d54840add294c3c562840f78764196.pack
Indexing objects: 100% (1944656/1944656), done.
fatal: pack has 1617280 unresolved deltas

real    0m41.714s
user    0m40.994s
sys     0m0.550s

Signed-off-by: Nguyễn Thái Ngọc Duy <[email-masked]>
---
 builtin/index-pack.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index dd1c5c9..cee83b9 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -62,6 +62,7 @@ static int nr_resolved_deltas;
 
 static int from_stdin;
 static int strict;
+static int verify;
 static int verbose;
 
 static struct progress *progress;
@@ -461,7 +462,7 @@ static void sha1_object(const void *data, unsigned long size,
 			enum object_type type, unsigned char *sha1)
 {
 	hash_sha1_file(data, size, typename(type), sha1);
-	if (has_sha1_file(sha1)) {
+	if ((strict || !verify) && has_sha1_file(sha1)) {
 		void *has_data;
 		enum object_type has_type;
 		unsigned long has_size;
@@ -1078,7 +1079,7 @@ static void show_pack_info(int stat_only)
 
 int cmd_index_pack(int argc, const char **argv, const char *prefix)
 {
-	int i, fix_thin_pack = 0, verify = 0, stat_only = 0, stat = 0;
+	int i, fix_thin_pack = 0, stat_only = 0, stat = 0;
 	const char *curr_pack, *curr_index;
 	const char *index_name = NULL, *pack_name = NULL;
 	const char *keep_name = NULL, *keep_msg = NULL;
-- 
1.7.8.36.g69ee2