[PATCH 2/4] fsck: check rev-index checksums

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <derrickstolee@github.com>

The previous change added calls to verify_pack_revindex() in
builtin/fsck.c, but the implementation of the method was left empty. Add
the first and most-obvious check to this method: checksum verification.

While here, create a helper method in the test script that makes it easy
to adjust the .rev file and check that 'git fsck' reports the correct
error message.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 pack-revindex.c          | 10 ++++++++++
 t/t5325-reverse-index.sh | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/pack-revindex.c b/pack-revindex.c
index c3f2aaa3fea..007a806994f 100644
--- a/pack-revindex.c
+++ b/pack-revindex.c
@@ -5,6 +5,7 @@
 #include "packfile.h"
 #include "config.h"
 #include "midx.h"
+#include "csum-file.h"
 
 struct revindex_entry {
 	off_t offset;
@@ -309,6 +310,15 @@ int load_pack_revindex(struct repository *r, struct packed_git *p)
  */
 int verify_pack_revindex(struct packed_git *p)
 {
+	/* Do not bother checking if not initialized. */
+	if (!p->revindex_map)
+		return 0;
+
+	if (!hashfile_checksum_valid((const unsigned char *)p->revindex_map, p->revindex_size)) {
+		error(_("invalid checksum"));
+		return -1;
+	}
+
 	return 0;
 }
 
diff --git a/t/t5325-reverse-index.sh b/t/t5325-reverse-index.sh
index 206c412f50b..6b7c709a1f6 100755
--- a/t/t5325-reverse-index.sh
+++ b/t/t5325-reverse-index.sh
@@ -145,4 +145,44 @@ test_expect_success 'fsck succeeds on good rev-index' '
 	)
 '
 
+test_expect_success 'set up rev-index corruption tests' '
+	git init corrupt &&
+	(
+		cd corrupt &&
+
+		test_commit commit &&
+		git -c pack.writeReverseIndex=true repack -ad &&
+
+		revfile=$(ls .git/objects/pack/pack-*.rev) &&
+		chmod a+w $revfile &&
+		cp $revfile $revfile.bak
+	)
+'
+
+corrupt_rev_and_verify () {
+	(
+		pos="$1" &&
+		value="$2" &&
+		error="$3" &&
+
+		cd corrupt &&
+		revfile=$(ls .git/objects/pack/pack-*.rev) &&
+
+		# Reset to original rev-file.
+		cp $revfile.bak $revfile &&
+
+		printf "$value" | dd of=$revfile bs=1 seek="$pos" conv=notrunc &&
+		test_must_fail git fsck 2>err &&
+		grep "$error" err
+	)
+}
+
+test_expect_success 'fsck catches invalid checksum' '
+	revfile=$(ls corrupt/.git/objects/pack/pack-*.rev) &&
+	orig_size=$(wc -c <$revfile) &&
+	hashpos=$((orig_size - 10)) &&
+	corrupt_rev_and_verify $hashpos bogus \
+		"invalid checksum"
+'
+
 test_done
-- 
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