[PATCH 2/2] upload-pack: handle unexpected delim packets

[Jeff King <peff@peff.net>]

When processing the arguments list for a v2 ls-refs or fetch command, we
loop like this:

  while (packet_reader_read(request) != PACKET_READ_FLUSH) {
          const char *arg = request->line;
	  ...handle arg...
  }

to read and handle packets until we see a flush. The hidden assumption
here is that anything except PACKET_READ_FLUSH will give us valid packet
data to read. But that's not true; PACKET_READ_DELIM or PACKET_READ_EOF
will leave packet->line as NULL, and we'll segfault trying to look at
it.

Instead, we should follow the more careful model demonstrated on the
client side (e.g., in process_capabilities_v2): keep looping as long
as we get normal packets, and then make sure that we broke out of the
loop due to a real flush. That fixes the segfault and correctly
diagnoses any unexpected input from the client.

Signed-off-by: Jeff King <peff@peff.net>
---
 ls-refs.c                      |  5 ++++-
 t/t5704-protocol-violations.sh | 33 +++++++++++++++++++++++++++++++++
 upload-pack.c                  |  5 ++++-
 3 files changed, 41 insertions(+), 2 deletions(-)
 create mode 100755 t/t5704-protocol-violations.sh

diff --git a/ls-refs.c b/ls-refs.c
index 818aef70a0..50d86866c6 100644
--- a/ls-refs.c
+++ b/ls-refs.c
@@ -93,7 +93,7 @@ int ls_refs(struct repository *r, struct argv_array *keys,
 
 	git_config(ls_refs_config, NULL);
 
-	while (packet_reader_read(request) != PACKET_READ_FLUSH) {
+	while (packet_reader_read(request) == PACKET_READ_NORMAL) {
 		const char *arg = request->line;
 		const char *out;
 
@@ -105,6 +105,9 @@ int ls_refs(struct repository *r, struct argv_array *keys,
 			argv_array_push(&data.prefixes, out);
 	}
 
+	if (request->status != PACKET_READ_FLUSH)
+		die(_("expected flush after ls-refs arguments"));
+
 	head_ref_namespaced(send_ref, &data);
 	for_each_namespaced_ref(send_ref, &data);
 	packet_flush(1);
diff --git a/t/t5704-protocol-violations.sh b/t/t5704-protocol-violations.sh
new file mode 100755
index 0000000000..950cfb21fe
--- /dev/null
+++ b/t/t5704-protocol-violations.sh
@@ -0,0 +1,33 @@
+#!/bin/sh
+
+test_description='Test responses to violations of the network protocol. In most
+of these cases it will generally be acceptable for one side to break off
+communications if the other side says something unexpected. We are mostly
+making sure that we do not segfault or otherwise behave badly.'
+. ./test-lib.sh
+
+test_expect_success 'extra delim packet in v2 ls-refs args' '
+	{
+		packetize command=ls-refs &&
+		printf 0001 &&
+		# protocol expects 0000 flush here
+		printf 0001
+	} >input &&
+	test_must_fail env GIT_PROTOCOL=version=2 \
+		git upload-pack . <input 2>err &&
+	test_i18ngrep "expected flush after ls-refs arguments" err
+'
+
+test_expect_success 'extra delim packet in v2 fetch args' '
+	{
+		packetize command=fetch &&
+		printf 0001 &&
+		# protocol expects 0000 flush here
+		printf 0001
+	} >input &&
+	test_must_fail env GIT_PROTOCOL=version=2 \
+		git upload-pack . <input 2>err &&
+	test_i18ngrep "expected flush after fetch arguments" err
+'
+
+test_done
diff --git a/upload-pack.c b/upload-pack.c
index c53249cac1..902d0ad5e1 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -1252,7 +1252,7 @@ static void process_args(struct packet_reader *request,
 			 struct upload_pack_data *data,
 			 struct object_array *want_obj)
 {
-	while (packet_reader_read(request) != PACKET_READ_FLUSH) {
+	while (packet_reader_read(request) == PACKET_READ_NORMAL) {
 		const char *arg = request->line;
 		const char *p;
 
@@ -1321,6 +1321,9 @@ static void process_args(struct packet_reader *request,
 		/* ignore unknown lines maybe? */
 		die("unexpected line: '%s'", arg);
 	}
+
+	if (request->status != PACKET_READ_FLUSH)
+		die(_("expected flush after fetch arguments"));
 }
 
 static int process_haves(struct oid_array *haves, struct oid_array *common,
-- 
2.26.0.581.g322f77c0ee