6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Matt Johnston <matt@xxxxxxxxxxxxxxxxxxxx>
[ Upstream commit f5d83cf0eeb90fade4d5c4d17d24b8bee9ceeecc ]
Ensure that the frag_list used for reassembly isn't shared with other
packets. This avoids incorrect reassembly when packets are cloned, and
prevents a memory leak due to circular references between fragments and
their skb_shared_info.
The upcoming MCTP-over-USB driver uses skb_clone which can trigger the
problem - other MCTP drivers don't share SKBs.
A kunit test is added to reproduce the issue.
Signed-off-by: Matt Johnston <matt@xxxxxxxxxxxxxxxxxxxx>
Fixes: 4a992bbd3650 ("mctp: Implement message fragmentation & reassembly")
Reviewed-by: Simon Horman <horms@xxxxxxxxxx>
Link: https://patch.msgid.link/20250306-matt-mctp-usb-v1-1-085502b3dd28@xxxxxxxxxxxxxxxxxxxx
Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
net/mctp/route.c | 10 +++-
net/mctp/test/route-test.c | 109 +++++++++++++++++++++++++++++++++++++
2 files changed, 117 insertions(+), 2 deletions(-)
diff --git a/net/mctp/route.c b/net/mctp/route.c
index 3f2bd65ff5e3c..4c460160914f0 100644
--- a/net/mctp/route.c
+++ b/net/mctp/route.c
@@ -332,8 +332,14 @@ static int mctp_frag_queue(struct mctp_sk_key *key, struct sk_buff *skb)
& MCTP_HDR_SEQ_MASK;
if (!key->reasm_head) {
- key->reasm_head = skb;
- key->reasm_tailp = &(skb_shinfo(skb)->frag_list);
+ /* Since we're manipulating the shared frag_list, ensure it isn't
+ * shared with any other SKBs.
+ */
+ key->reasm_head = skb_unshare(skb, GFP_ATOMIC);
+ if (!key->reasm_head)
+ return -ENOMEM;
+
+ key->reasm_tailp = &(skb_shinfo(key->reasm_head)->frag_list);
key->last_seq = this_seq;
return 0;
}
diff --git a/net/mctp/test/route-test.c b/net/mctp/test/route-test.c
index 17165b86ce22d..06c1897b685a8 100644
--- a/net/mctp/test/route-test.c
+++ b/net/mctp/test/route-test.c
@@ -921,6 +921,114 @@ static void mctp_test_route_input_sk_fail_frag(struct kunit *test)
__mctp_route_test_fini(test, dev, rt, sock);
}
+/* Input route to socket, using a fragmented message created from clones.
+ */
+static void mctp_test_route_input_cloned_frag(struct kunit *test)
+{
+ /* 5 packet fragments, forming 2 complete messages */
+ const struct mctp_hdr hdrs[5] = {
+ RX_FRAG(FL_S, 0),
+ RX_FRAG(0, 1),
+ RX_FRAG(FL_E, 2),
+ RX_FRAG(FL_S, 0),
+ RX_FRAG(FL_E, 1),
+ };
+ struct mctp_test_route *rt;
+ struct mctp_test_dev *dev;
+ struct sk_buff *skb[5];
+ struct sk_buff *rx_skb;
+ struct socket *sock;
+ size_t data_len;
+ u8 compare[100];
+ u8 flat[100];
+ size_t total;
+ void *p;
+ int rc;
+
+ /* Arbitrary length */
+ data_len = 3;
+ total = data_len + sizeof(struct mctp_hdr);
+
+ __mctp_route_test_init(test, &dev, &rt, &sock, MCTP_NET_ANY);
+
+ /* Create a single skb initially with concatenated packets */
+ skb[0] = mctp_test_create_skb(&hdrs[0], 5 * total);
+ mctp_test_skb_set_dev(skb[0], dev);
+ memset(skb[0]->data, 0 * 0x11, skb[0]->len);
+ memcpy(skb[0]->data, &hdrs[0], sizeof(struct mctp_hdr));
+
+ /* Extract and populate packets */
+ for (int i = 1; i < 5; i++) {
+ skb[i] = skb_clone(skb[i - 1], GFP_ATOMIC);
+ KUNIT_ASSERT_TRUE(test, skb[i]);
+ p = skb_pull(skb[i], total);
+ KUNIT_ASSERT_TRUE(test, p);
+ skb_reset_network_header(skb[i]);
+ memcpy(skb[i]->data, &hdrs[i], sizeof(struct mctp_hdr));
+ memset(&skb[i]->data[sizeof(struct mctp_hdr)], i * 0x11, data_len);
+ }
+ for (int i = 0; i < 5; i++)
+ skb_trim(skb[i], total);
+
+ /* SOM packets have a type byte to match the socket */
+ skb[0]->data[4] = 0;
+ skb[3]->data[4] = 0;
+
+ skb_dump("pkt1 ", skb[0], false);
+ skb_dump("pkt2 ", skb[1], false);
+ skb_dump("pkt3 ", skb[2], false);
+ skb_dump("pkt4 ", skb[3], false);
+ skb_dump("pkt5 ", skb[4], false);
+
+ for (int i = 0; i < 5; i++) {
+ KUNIT_EXPECT_EQ(test, refcount_read(&skb[i]->users), 1);
+ /* Take a reference so we can check refcounts at the end */
+ skb_get(skb[i]);
+ }
+
+ /* Feed the fragments into MCTP core */
+ for (int i = 0; i < 5; i++) {
+ rc = mctp_route_input(&rt->rt, skb[i]);
+ KUNIT_EXPECT_EQ(test, rc, 0);
+ }
+
+ /* Receive first reassembled message */
+ rx_skb = skb_recv_datagram(sock->sk, MSG_DONTWAIT, &rc);
+ KUNIT_EXPECT_EQ(test, rc, 0);
+ KUNIT_EXPECT_EQ(test, rx_skb->len, 3 * data_len);
+ rc = skb_copy_bits(rx_skb, 0, flat, rx_skb->len);
+ for (int i = 0; i < rx_skb->len; i++)
+ compare[i] = (i / data_len) * 0x11;
+ /* Set type byte */
+ compare[0] = 0;
+
+ KUNIT_EXPECT_MEMEQ(test, flat, compare, rx_skb->len);
+ KUNIT_EXPECT_EQ(test, refcount_read(&rx_skb->users), 1);
+ kfree_skb(rx_skb);
+
+ /* Receive second reassembled message */
+ rx_skb = skb_recv_datagram(sock->sk, MSG_DONTWAIT, &rc);
+ KUNIT_EXPECT_EQ(test, rc, 0);
+ KUNIT_EXPECT_EQ(test, rx_skb->len, 2 * data_len);
+ rc = skb_copy_bits(rx_skb, 0, flat, rx_skb->len);
+ for (int i = 0; i < rx_skb->len; i++)
+ compare[i] = (i / data_len + 3) * 0x11;
+ /* Set type byte */
+ compare[0] = 0;
+
+ KUNIT_EXPECT_MEMEQ(test, flat, compare, rx_skb->len);
+ KUNIT_EXPECT_EQ(test, refcount_read(&rx_skb->users), 1);
+ kfree_skb(rx_skb);
+
+ /* Check input skb refcounts */
+ for (int i = 0; i < 5; i++) {
+ KUNIT_EXPECT_EQ(test, refcount_read(&skb[i]->users), 1);
+ kfree_skb(skb[i]);
+ }
+
+ __mctp_route_test_fini(test, dev, rt, sock);
+}
+
#if IS_ENABLED(CONFIG_MCTP_FLOWS)
static void mctp_test_flow_init(struct kunit *test,
@@ -1144,6 +1252,7 @@ static struct kunit_case mctp_test_cases[] = {
KUNIT_CASE(mctp_test_packet_flow),
KUNIT_CASE(mctp_test_fragment_flow),
KUNIT_CASE(mctp_test_route_output_key_create),
+ KUNIT_CASE(mctp_test_route_input_cloned_frag),
{}
};
--
2.39.5
