Merge branch 'np/pack-safer'

* np/pack-safer:
  t5303: fix printf format string for portability
  t5303: work around printf breakage in dash
  pack-objects: don't leak pack window reference when splitting packs
  extend test coverage for latest pack corruption resilience improvements
  pack-objects: allow "fixing" a corrupted pack without a full repack
  make find_pack_revindex() aware of the nasty world
  make check_object() resilient to pack corruptions
  make packed_object_info() resilient to pack corruptions
  make unpack_object_header() non fatal
  better validation on delta base object offsets
  close another possibility for propagating pack corruption

8 files changed, 224 insertions, 49 deletions

diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index 59ae64d83..67eefa293 100644
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -286,6 +286,7 @@ static unsigned long write_object(struct sha1file *f,
 				 */
 
 	if (!to_reuse) {
+		no_reuse:
 		if (!usable_delta) {
 			buf = read_sha1_file(entry->idx.sha1, &type, &size);
 			if (!buf)
@@ -367,46 +368,60 @@ static unsigned long write_object(struct sha1file *f,
 		struct revindex_entry *revidx;
 		off_t offset;
 
-		if (entry->delta) {
+		if (entry->delta)
 			type = (allow_ofs_delta && entry->delta->idx.offset) ?
 				OBJ_OFS_DELTA : OBJ_REF_DELTA;
-			reused_delta++;
-		}
 		hdrlen = encode_header(type, entry->size, header);
+
 		offset = entry->in_pack_offset;
 		revidx = find_pack_revindex(p, offset);
 		datalen = revidx[1].offset - offset;
 		if (!pack_to_stdout && p->index_version > 1 &&
-		    check_pack_crc(p, &w_curs, offset, datalen, revidx->nr))
-			die("bad packed object CRC for %s", sha1_to_hex(entry->idx.sha1));
+		    check_pack_crc(p, &w_curs, offset, datalen, revidx->nr)) {
+			error("bad packed object CRC for %s", sha1_to_hex(entry->idx.sha1));
+			unuse_pack(&w_curs);
+			goto no_reuse;
+		}
+
 		offset += entry->in_pack_header_size;
 		datalen -= entry->in_pack_header_size;
+		if (!pack_to_stdout && p->index_version == 1 &&
+		    check_pack_inflate(p, &w_curs, offset, datalen, entry->size)) {
+			error("corrupt packed object for %s", sha1_to_hex(entry->idx.sha1));
+			unuse_pack(&w_curs);
+			goto no_reuse;
+		}
+
 		if (type == OBJ_OFS_DELTA) {
 			off_t ofs = entry->idx.offset - entry->delta->idx.offset;
 			unsigned pos = sizeof(dheader) - 1;
 			dheader[pos] = ofs & 127;
 			while (ofs >>= 7)
 				dheader[--pos] = 128 | (--ofs & 127);
-			if (limit && hdrlen + sizeof(dheader) - pos + datalen + 20 >= limit)
+			if (limit && hdrlen + sizeof(dheader) - pos + datalen + 20 >= limit) {
+				unuse_pack(&w_curs);
 				return 0;
+			}
 			sha1write(f, header, hdrlen);
 			sha1write(f, dheader + pos, sizeof(dheader) - pos);
 			hdrlen += sizeof(dheader) - pos;
+			reused_delta++;
 		} else if (type == OBJ_REF_DELTA) {
-			if (limit && hdrlen + 20 + datalen + 20 >= limit)
+			if (limit && hdrlen + 20 + datalen + 20 >= limit) {
+				unuse_pack(&w_curs);
 				return 0;
+			}
 			sha1write(f, header, hdrlen);
 			sha1write(f, entry->delta->idx.sha1, 20);
 			hdrlen += 20;
+			reused_delta++;
 		} else {
-			if (limit && hdrlen + datalen + 20 >= limit)
+			if (limit && hdrlen + datalen + 20 >= limit) {
+				unuse_pack(&w_curs);
 				return 0;
+			}
 			sha1write(f, header, hdrlen);
 		}
-
-		if (!pack_to_stdout && p->index_version == 1 &&
-		    check_pack_inflate(p, &w_curs, offset, datalen, entry->size))
-			die("corrupt packed object for %s", sha1_to_hex(entry->idx.sha1));
 		copy_pack_data(f, p, &w_curs, offset, datalen);
 		unuse_pack(&w_curs);
 		reused++;
@@ -1016,9 +1031,11 @@ static void check_object(struct object_entry *entry)
 		 * We want in_pack_type even if we do not reuse delta
 		 * since non-delta representations could still be reused.
 		 */
-		used = unpack_object_header_gently(buf, avail,
+		used = unpack_object_header_buffer(buf, avail,
 						   &entry->in_pack_type,
 						   &entry->size);
+		if (used == 0)
+			goto give_up;
 
 		/*
 		 * Determine if this is a delta and if so whether we can
@@ -1030,6 +1047,8 @@ static void check_object(struct object_entry *entry)
 			/* Not a delta hence we've already got all we need. */
 			entry->type = entry->in_pack_type;
 			entry->in_pack_header_size = used;
+			if (entry->type < OBJ_COMMIT || entry->type > OBJ_BLOB)
+				goto give_up;
 			unuse_pack(&w_curs);
 			return;
 		case OBJ_REF_DELTA:
@@ -1046,19 +1065,25 @@ static void check_object(struct object_entry *entry)
 			ofs = c & 127;
 			while (c & 128) {
 				ofs += 1;
-				if (!ofs || MSB(ofs, 7))
-					die("delta base offset overflow in pack for %s",
-					    sha1_to_hex(entry->idx.sha1));
+				if (!ofs || MSB(ofs, 7)) {
+					error("delta base offset overflow in pack for %s",
+					      sha1_to_hex(entry->idx.sha1));
+					goto give_up;
+				}
 				c = buf[used_0++];
 				ofs = (ofs << 7) + (c & 127);
 			}
-			if (ofs >= entry->in_pack_offset)
-				die("delta base offset out of bound for %s",
-				    sha1_to_hex(entry->idx.sha1));
 			ofs = entry->in_pack_offset - ofs;
+			if (ofs <= 0 || ofs >= entry->in_pack_offset) {
+				error("delta base offset out of bound for %s",
+				      sha1_to_hex(entry->idx.sha1));
+				goto give_up;
+			}
 			if (reuse_delta && !entry->preferred_base) {
 				struct revindex_entry *revidx;
 				revidx = find_pack_revindex(p, ofs);
+				if (!revidx)
+					goto give_up;
 				base_ref = nth_packed_object_sha1(p, revidx->nr);
 			}
 			entry->in_pack_header_size = used + used_0;
@@ -1078,6 +1103,7 @@ static void check_object(struct object_entry *entry)
 			 */
 			entry->type = entry->in_pack_type;
 			entry->delta = base_entry;
+			entry->delta_size = entry->size;
 			entry->delta_sibling = base_entry->delta_child;
 			base_entry->delta_child = entry;
 			unuse_pack(&w_curs);
@@ -1092,6 +1118,8 @@ static void check_object(struct object_entry *entry)
 			 */
 			entry->size = get_size_from_delta(p, &w_curs,
 					entry->in_pack_offset + entry->in_pack_header_size);
+			if (entry->size == 0)
+				goto give_up;
 			unuse_pack(&w_curs);
 			return;
 		}
@@ -1101,6 +1129,7 @@ static void check_object(struct object_entry *entry)
 		 * with sha1_object_info() to find about the object type
 		 * at this point...
 		 */
+		give_up:
 		unuse_pack(&w_curs);
 	}
 
@@ -1712,6 +1741,16 @@ static void prepare_pack(int window, int depth)
 
 	get_object_details();
 
+	/*
+	 * If we're locally repacking then we need to be doubly careful
+	 * from now on in order to make sure no stealth corruption gets
+	 * propagated to the new pack.  Clients receiving streamed packs
+	 * should validate everything they get anyway so no need to incur
+	 * the additional cost here in that case.
+	 */
+	if (!pack_to_stdout)
+		do_check_packed_object_crc = 1;
+
 	if (!nr_objects || !window || !depth)
 		return;
 
diff --git a/builtin-unpack-objects.c b/builtin-unpack-objects.c
index 9f4bdd329..47ed61067 100644
--- a/builtin-unpack-objects.c
+++ b/builtin-unpack-objects.c
@@ -370,6 +370,8 @@ static void unpack_delta_entry(enum object_type type, unsigned long delta_size,
 			base_offset = (base_offset << 7) + (c & 127);
 		}
 		base_offset = obj_list[nr].offset - base_offset;
+		if (base_offset <= 0 || base_offset >= obj_list[nr].offset)
+			die("offset value out of bound for delta base object");
 
 		delta_data = get_data(delta_size);
 		if (dry_run || !delta_data) {
diff --git a/cache.h b/cache.h
index c776f2f5a..3b5f0c4c0 100644
--- a/cache.h
+++ b/cache.h
@@ -574,6 +574,9 @@ extern int force_object_loose(const unsigned char *sha1, time_t mtime);
 /* just like read_sha1_file(), but non fatal in presence of bad objects */
 extern void *read_object(const unsigned char *sha1, enum object_type *type, unsigned long *size);
 
+/* global flag to enable extra checks when accessing packed objects */
+extern int do_check_packed_object_crc;
+
 extern int check_sha1_signature(const unsigned char *sha1, void *buf, unsigned long size, const char *type);
 
 extern int move_temp_to_file(const char *tmpfile, const char *filename);
@@ -762,7 +765,7 @@ extern const unsigned char *nth_packed_object_sha1(struct packed_git *, uint32_t
 extern off_t nth_packed_object_offset(const struct packed_git *, uint32_t);
 extern off_t find_pack_entry_one(const unsigned char *, struct packed_git *);
 extern void *unpack_entry(struct packed_git *, off_t, enum object_type *, unsigned long *);
-extern unsigned long unpack_object_header_gently(const unsigned char *buf, unsigned long len, enum object_type *type, unsigned long *sizep);
+extern unsigned long unpack_object_header_buffer(const unsigned char *buf, unsigned long len, enum object_type *type, unsigned long *sizep);
 extern unsigned long get_size_from_delta(struct packed_git *, struct pack_window **, off_t);
 extern const char *packed_object_info_detail(struct packed_git *, off_t, unsigned long *, unsigned long *, unsigned int *, unsigned char *);
 extern int matches_pack_name(struct packed_git *p, const char *name);
diff --git a/index-pack.c b/index-pack.c
index fe75332a9..60ed41a99 100644
--- a/index-pack.c
+++ b/index-pack.c
@@ -338,7 +338,7 @@ static void *unpack_raw_entry(struct object_entry *obj, union delta_base *delta_
 			base_offset = (base_offset << 7) + (c & 127);
 		}
 		delta_base->offset = obj->idx.offset - base_offset;
-		if (delta_base->offset >= obj->idx.offset)
+		if (delta_base->offset <= 0 || delta_base->offset >= obj->idx.offset)
 			bad_object(obj->idx.offset, "delta base offset is out of bound");
 		break;
 	case OBJ_COMMIT:
diff --git a/pack-revindex.c b/pack-revindex.c
index 6096b6224..1de53c893 100644
--- a/pack-revindex.c
+++ b/pack-revindex.c
@@ -140,7 +140,8 @@ struct revindex_entry *find_pack_revindex(struct packed_git *p, off_t ofs)
 		else
 			lo = mi + 1;
 	} while (lo < hi);
-	die("internal error: pack revindex corrupt");
+	error("bad offset for revindex");
+	return NULL;
 }
 
 void discard_revindex(void)
diff --git a/sha1_file.c b/sha1_file.c
index 491220572..0fa65baa5 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1122,7 +1122,8 @@ static int legacy_loose_object(unsigned char *map)
 		return 0;
 }
 
-unsigned long unpack_object_header_gently(const unsigned char *buf, unsigned long len, enum object_type *type, unsigned long *sizep)
+unsigned long unpack_object_header_buffer(const unsigned char *buf,
+		unsigned long len, enum object_type *type, unsigned long *sizep)
 {
 	unsigned shift;
 	unsigned char c;
@@ -1134,10 +1135,10 @@ unsigned long unpack_object_header_gently(const unsigned char *buf, unsigned lon
 	size = c & 15;
 	shift = 4;
 	while (c & 0x80) {
-		if (len <= used)
-			return 0;
-		if (sizeof(long) * 8 <= shift)
+		if (len <= used || sizeof(long) * 8 <= shift) {
+			error("bad object header");
 			return 0;
+		}
 		c = buf[used++];
 		size += (c & 0x7f) << shift;
 		shift += 7;
@@ -1176,7 +1177,7 @@ static int unpack_sha1_header(z_stream *stream, unsigned char *map, unsigned lon
 	 * really worth it and we don't write it any longer.  But we
 	 * can still read it.
 	 */
-	used = unpack_object_header_gently(map, mapsize, &type, &size);
+	used = unpack_object_header_buffer(map, mapsize, &type, &size);
 	if (!used || !valid_loose_object_type[type])
 		return -1;
 	map += used;
@@ -1325,8 +1326,10 @@ unsigned long get_size_from_delta(struct packed_git *p,
 	} while ((st == Z_OK || st == Z_BUF_ERROR) &&
 		 stream.total_out < sizeof(delta_head));
 	inflateEnd(&stream);
-	if ((st != Z_STREAM_END) && stream.total_out != sizeof(delta_head))
-		die("delta data unpack-initial failed");
+	if ((st != Z_STREAM_END) && stream.total_out != sizeof(delta_head)) {
+		error("delta data unpack-initial failed");
+		return 0;
+	}
 
 	/* Examine the initial part of the delta to figure out
 	 * the result size.
@@ -1367,7 +1370,7 @@ static off_t get_delta_base(struct packed_git *p,
 			base_offset = (base_offset << 7) + (c & 127);
 		}
 		base_offset = delta_obj_offset - base_offset;
-		if (base_offset >= delta_obj_offset)
+		if (base_offset <= 0 || base_offset >= delta_obj_offset)
 			return 0;  /* out of bound */
 		*curpos += used;
 	} else if (type == OBJ_REF_DELTA) {
@@ -1393,15 +1396,32 @@ static int packed_delta_info(struct packed_git *p,
 	off_t base_offset;
 
 	base_offset = get_delta_base(p, w_curs, &curpos, type, obj_offset);
+	if (!base_offset)
+		return OBJ_BAD;
 	type = packed_object_info(p, base_offset, NULL);
+	if (type <= OBJ_NONE) {
+		struct revindex_entry *revidx;
+		const unsigned char *base_sha1;
+		revidx = find_pack_revindex(p, base_offset);
+		if (!revidx)
+			return OBJ_BAD;
+		base_sha1 = nth_packed_object_sha1(p, revidx->nr);
+		mark_bad_packed_object(p, base_sha1);
+		type = sha1_object_info(base_sha1, NULL);
+		if (type <= OBJ_NONE)
+			return OBJ_BAD;
+	}
 
 	/* We choose to only get the type of the base object and
 	 * ignore potentially corrupt pack file that expects the delta
 	 * based on a base with a wrong size.  This saves tons of
 	 * inflate() calls.
 	 */
-	if (sizep)
+	if (sizep) {
 		*sizep = get_size_from_delta(p, w_curs, curpos);
+		if (*sizep == 0)
+			type = OBJ_BAD;
+	}
 
 	return type;
 }
@@ -1423,10 +1443,11 @@ static int unpack_object_header(struct packed_git *p,
 	 * insane, so we know won't exceed what we have been given.
 	 */
 	base = use_pack(p, w_curs, *curpos, &left);
-	used = unpack_object_header_gently(base, left, &type, sizep);
-	if (!used)
-		die("object offset outside of pack file");
-	*curpos += used;
+	used = unpack_object_header_buffer(base, left, &type, sizep);
+	if (!used) {
+		type = OBJ_BAD;
+	} else
+		*curpos += used;
 
 	return type;
 }
@@ -1510,8 +1531,9 @@ static int packed_object_info(struct packed_git *p, off_t obj_offset,
 			*sizep = size;
 		break;
 	default:
-		die("pack %s contains unknown object type %d",
-		    p->pack_name, type);
+		error("unknown object type %i at offset %"PRIuMAX" in %s",
+		      type, (uintmax_t)obj_offset, p->pack_name);
+		type = OBJ_BAD;
 	}
 	unuse_pack(&w_curs);
 	return type;
@@ -1675,9 +1697,12 @@ static void *unpack_delta_entry(struct packed_git *p,
 		 * This is costly but should happen only in the presence
 		 * of a corrupted pack, and is better than failing outright.
 		 */
-		struct revindex_entry *revidx = find_pack_revindex(p, base_offset);
-		const unsigned char *base_sha1 =
-					nth_packed_object_sha1(p, revidx->nr);
+		struct revindex_entry *revidx;
+		const unsigned char *base_sha1;
+		revidx = find_pack_revindex(p, base_offset);
+		if (!revidx)
+			return NULL;
+		base_sha1 = nth_packed_object_sha1(p, revidx->nr);
 		error("failed to read delta base object %s"
 		      " at offset %"PRIuMAX" from %s",
 		      sha1_to_hex(base_sha1), (uintmax_t)base_offset,
@@ -1706,6 +1731,8 @@ static void *unpack_delta_entry(struct packed_git *p,
 	return result;
 }
 
+int do_check_packed_object_crc;
+
 void *unpack_entry(struct packed_git *p, off_t obj_offset,
 		   enum object_type *type, unsigned long *sizep)
 {
@@ -1713,6 +1740,19 @@ void *unpack_entry(struct packed_git *p, off_t obj_offset,
 	off_t curpos = obj_offset;
 	void *data;
 
+	if (do_check_packed_object_crc && p->index_version > 1) {
+		struct revindex_entry *revidx = find_pack_revindex(p, obj_offset);
+		unsigned long len = revidx[1].offset - obj_offset;
+		if (check_pack_crc(p, &w_curs, obj_offset, len, revidx->nr)) {
+			const unsigned char *sha1 =
+				nth_packed_object_sha1(p, revidx->nr);
+			error("bad packed object CRC for %s",
+			      sha1_to_hex(sha1));
+			mark_bad_packed_object(p, sha1);
+			return NULL;
+		}
+	}
+
 	*type = unpack_object_header(p, &w_curs, &curpos, sizep);
 	switch (*type) {
 	case OBJ_OFS_DELTA:
@@ -1966,7 +2006,14 @@ int sha1_object_info(const unsigned char *sha1, unsigned long *sizep)
 		if (!find_pack_entry(sha1, &e, NULL))
 			return status;
 	}
-	return packed_object_info(e.p, e.offset, sizep);
+
+	status = packed_object_info(e.p, e.offset, sizep);
+	if (status < 0) {
+		mark_bad_packed_object(e.p, sha1);
+		status = sha1_object_info(sha1, sizep);
+	}
+
+	return status;
 }
 
 static void *read_packed_sha1(const unsigned char *sha1,
diff --git a/t/t5302-pack-index.sh b/t/t5302-pack-index.sh
index b0b0fdaca..884e24253 100755
--- a/t/t5302-pack-index.sh
+++ b/t/t5302-pack-index.sh
@@ -196,7 +196,8 @@ test_expect_success \
 
 test_expect_success \
     '[index v2] 5) pack-objects refuses to reuse corrupted data' \
-    'test_must_fail git pack-objects test-5 <obj-list'
+    'test_must_fail git pack-objects test-5 <obj-list &&
+     test_must_fail git pack-objects --no-reuse-object test-6 <obj-list'
 
 test_expect_success \
     '[index v2] 6) verify-pack detects CRC mismatch' \
diff --git a/t/t5303-pack-corruption-resilience.sh b/t/t5303-pack-corruption-resilience.sh
index 31b20b21d..d4e30fc43 100755
--- a/t/t5303-pack-corruption-resilience.sh
+++ b/t/t5303-pack-corruption-resilience.sh
@@ -41,11 +41,17 @@ create_new_pack() {
     git verify-pack -v ${pack}.pack
 }
 
+do_repack() {
+    pack=`printf "$blob_1\n$blob_2\n$blob_3\n" |
+          git pack-objects $@ .git/objects/pack/pack` &&
+    pack=".git/objects/pack/pack-${pack}"
+}
+
 do_corrupt_object() {
     ofs=`git show-index < ${pack}.idx | grep $1 | cut -f1 -d" "` &&
     ofs=$(($ofs + $2)) &&
     chmod +w ${pack}.pack &&
-    dd if=/dev/zero of=${pack}.pack count=1 bs=1 conv=notrunc seek=$ofs &&
+    dd of=${pack}.pack count=1 bs=1 conv=notrunc seek=$ofs &&
     test_must_fail git verify-pack ${pack}.pack
 }
 
@@ -60,7 +66,7 @@ test_expect_success \
 
 test_expect_success \
     'create corruption in header of first object' \
-    'do_corrupt_object $blob_1 0 &&
+    'do_corrupt_object $blob_1 0 < /dev/zero &&
      test_must_fail git cat-file blob $blob_1 > /dev/null &&
      test_must_fail git cat-file blob $blob_2 > /dev/null &&
      test_must_fail git cat-file blob $blob_3 > /dev/null'
@@ -119,7 +125,7 @@ test_expect_success \
     'create corruption in header of first delta' \
     'create_new_pack &&
      git prune-packed &&
-     do_corrupt_object $blob_2 0 &&
+     do_corrupt_object $blob_2 0 < /dev/zero &&
      git cat-file blob $blob_1 > /dev/null &&
      test_must_fail git cat-file blob $blob_2 > /dev/null &&
      test_must_fail git cat-file blob $blob_3 > /dev/null'
@@ -134,6 +140,15 @@ test_expect_success \
      git cat-file blob $blob_3 > /dev/null'
 
 test_expect_success \
+    '... and then a repack "clears" the corruption' \
+    'do_repack &&
+     git prune-packed &&
+     git verify-pack ${pack}.pack &&
+     git cat-file blob $blob_1 > /dev/null &&
+     git cat-file blob $blob_2 > /dev/null &&
+     git cat-file blob $blob_3 > /dev/null'
+
+test_expect_success \
     'create corruption in data of first delta' \
     'create_new_pack &&
      git prune-packed &&
@@ -153,10 +168,19 @@ test_expect_success \
      git cat-file blob $blob_3 > /dev/null'
 
 test_expect_success \
+    '... and then a repack "clears" the corruption' \
+    'do_repack &&
+     git prune-packed &&
+     git verify-pack ${pack}.pack &&
+     git cat-file blob $blob_1 > /dev/null &&
+     git cat-file blob $blob_2 > /dev/null &&
+     git cat-file blob $blob_3 > /dev/null'
+
+test_expect_success \
     'corruption in delta base reference of first delta (OBJ_REF_DELTA)' \
     'create_new_pack &&
      git prune-packed &&
-     do_corrupt_object $blob_2 2 &&
+     do_corrupt_object $blob_2 2 < /dev/zero &&
      git cat-file blob $blob_1 > /dev/null &&
      test_must_fail git cat-file blob $blob_2 > /dev/null &&
      test_must_fail git cat-file blob $blob_3 > /dev/null'
@@ -171,17 +195,75 @@ test_expect_success \
      git cat-file blob $blob_3 > /dev/null'
 
 test_expect_success \
-    'corruption in delta base reference of first delta (OBJ_OFS_DELTA)' \
+    '... and then a repack "clears" the corruption' \
+    'do_repack &&
+     git prune-packed &&
+     git verify-pack ${pack}.pack &&
+     git cat-file blob $blob_1 > /dev/null &&
+     git cat-file blob $blob_2 > /dev/null &&
+     git cat-file blob $blob_3 > /dev/null'
+
+test_expect_success \
+    'corruption #0 in delta base reference of first delta (OBJ_OFS_DELTA)' \
     'create_new_pack --delta-base-offset &&
      git prune-packed &&
-     do_corrupt_object $blob_2 2 &&
+     do_corrupt_object $blob_2 2 < /dev/zero &&
      git cat-file blob $blob_1 > /dev/null &&
      test_must_fail git cat-file blob $blob_2 > /dev/null &&
      test_must_fail git cat-file blob $blob_3 > /dev/null'
 
 test_expect_success \
-    '... and a redundant pack allows for full recovery too' \
+    '... but having a loose copy allows for full recovery' \
     'mv ${pack}.idx tmp &&
+     git hash-object -t blob -w file_2 &&
+     mv tmp ${pack}.idx &&
+     git cat-file blob $blob_1 > /dev/null &&
+     git cat-file blob $blob_2 > /dev/null &&
+     git cat-file blob $blob_3 > /dev/null'
+
+test_expect_success \
+    '... and then a repack "clears" the corruption' \
+    'do_repack --delta-base-offset &&
+     git prune-packed &&
+     git verify-pack ${pack}.pack &&
+     git cat-file blob $blob_1 > /dev/null &&
+     git cat-file blob $blob_2 > /dev/null &&
+     git cat-file blob $blob_3 > /dev/null'
+
+test_expect_success \
+    'corruption #1 in delta base reference of first delta (OBJ_OFS_DELTA)' \
+    'create_new_pack --delta-base-offset &&
+     git prune-packed &&
+     printf "\001" | do_corrupt_object $blob_2 2 &&
+     git cat-file blob $blob_1 > /dev/null &&
+     test_must_fail git cat-file blob $blob_2 > /dev/null &&
+     test_must_fail git cat-file blob $blob_3 > /dev/null'
+
+test_expect_success \
+    '... but having a loose copy allows for full recovery' \
+    'mv ${pack}.idx tmp &&
+     git hash-object -t blob -w file_2 &&
+     mv tmp ${pack}.idx &&
+     git cat-file blob $blob_1 > /dev/null &&
+     git cat-file blob $blob_2 > /dev/null &&
+     git cat-file blob $blob_3 > /dev/null'
+
+test_expect_success \
+    '... and then a repack "clears" the corruption' \
+    'do_repack --delta-base-offset &&
+     git prune-packed &&
+     git verify-pack ${pack}.pack &&
+     git cat-file blob $blob_1 > /dev/null &&
+     git cat-file blob $blob_2 > /dev/null &&
+     git cat-file blob $blob_3 > /dev/null'
+
+test_expect_success \
+    '... and a redundant pack allows for full recovery too' \
+    'do_corrupt_object $blob_2 2 < /dev/zero &&
+     git cat-file blob $blob_1 > /dev/null &&
+     test_must_fail git cat-file blob $blob_2 > /dev/null &&
+     test_must_fail git cat-file blob $blob_3 > /dev/null &&
+     mv ${pack}.idx tmp &&
      git hash-object -t blob -w file_1 &&
      git hash-object -t blob -w file_2 &&
      printf "$blob_1\n$blob_2\n" | git pack-objects .git/objects/pack/pack &&