pack-objects: clamp negative depth to 0

peff · gitster · commit 6d52b6a5dfe0 · 2021-05-03T14:30:46.000+09:00
A negative delta depth makes no sense, and the code is not prepared to
handle it. If passed "--depth=-1" on the command line, then this line
from break_delta_chains():

	cur-&gt;depth = (total_depth--) % (depth + 1);

triggers a divide-by-zero. This is undefined behavior according to the C
standard, but on POSIX systems results in SIGFPE killing the process.
This is certainly one way to inform the use that the command was
invalid, but it's a bit friendlier to just treat it as "don't allow any
deltas", which we already do for --depth=0.

Signed-off-by: Jeff King &lt;peff@peff.net&gt;
Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
@@ -3861,6 +3861,8 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	if (pack_to_stdout != !base_name || argc)
 		usage_with_options(pack_usage, pack_objects_options);
 
+	if (depth < 0)
+		depth = 0;
 	if (depth >= (1 << OE_DEPTH_BITS)) {
 		warning(_("delta chain depth %d is too deep, forcing %d"),
 			depth, (1 << OE_DEPTH_BITS) - 1);
diff --git a/t/t5316-pack-delta-depth.sh b/t/t5316-pack-delta-depth.sh
@@ -102,4 +102,11 @@ test_expect_success '--depth=0 disables deltas' '
 	test_cmp expect actual
 '
 
+test_expect_success 'negative depth disables deltas' '
+	pack=$(git pack-objects --all --depth=-1 </dev/null pack) &&
+	echo 0 >expect &&
+	max_chain pack-$pack.pack >actual &&
+	test_cmp expect actual
+'
+
 test_done
