mptcp: fix spurious retransmissions

Syzkaller was able to trigger the following splat again: WARNING: CPU: 1 PID: 12512 at net/mptcp/protocol.c:761 mptcp_reset_timer+0x12a/0x160 net/mptcp/protocol.c:761 Modules linked in: CPU: 1 PID: 12512 Comm: kworker/1:6 Not tainted 5.10.0-rc6 #52 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 Workqueue: events mptcp_worker RIP: 0010:mptcp_reset_timer+0x12a/0x160 net/mptcp/protocol.c:761 Code: e8 4b 0c ad ff e8 56 21 88 fe 48 b8 00 00 00 00 00 fc ff df 48 c7 04 03 00 00 00 00 48 83 c4 40 5b 5d 41 5c c3 e8 36 21 88 fe <0f> 0b 41 bc c8 00 00 00 eb 98 e8 e7 b1 af fe e9 30 ff ff ff 48 c7 RSP: 0018:ffffc900018c7c68 EFLAGS: 00010293 RAX: ffff888108cb1c80 RBX: 1ffff92000318f8d RCX: ffffffff82ad0307 RDX: 0000000000000000 RSI: ffffffff82ad036a RDI: 0000000000000007 RBP: ffff888113e2d000 R08: ffff888108cb1c80 R09: ffffed10227c5ab7 R10: ffff888113e2d5b7 R11: ffffed10227c5ab6 R12: 0000000000000000 R13: ffff88801f100000 R14: ffff888113e2d5b0 R15: 0000000000000001 FS: 0000000000000000(0000) GS:ffff88811b500000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fd76a874ef8 CR3: 000000001689c005 CR4: 0000000000170ee0 Call Trace: mptcp_worker+0xaa4/0x1560 net/mptcp/protocol.c:2334 process_one_work+0x8d3/0x1200 kernel/workqueue.c:2272 worker_thread+0x9c/0x1090 kernel/workqueue.c:2418 kthread+0x303/0x410 kernel/kthread.c:292 ret_from_fork+0x22/0x30 arch/x86/entry/entry_64.S:296 The mptcp_worker tries to update the MPTCP retransmission timer even if such timer is not currently scheduled. The mptcp_rtx_head() return value is bogus: we can have enqueued data not yet transmitted. The above may additionally cause spurious, unneeded MPTCP-level retransmissions. Fix the issue adding an explicit clearing of the rtx queue before trying to retransmit and checking for unacked data. Additionally drop an unneeded timer stop call and the unused mptcp_rtx_tail() helper. Reported-by: Christoph Paasch <cpaasch@apple.com> Fixes: 6e628cd ("mptcp: use mptcp release_cb for delayed tasks") Signed-off-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com> Signed-off-by: David S. Miller <davem@davemloft.net>
multipath-tcp · Feb 12, 2021 · 64b9cea · 64b9cea
1 parent dd91341
commit 64b9cea
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Showing 2 changed files with 3 additions and 11 deletions.
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
@@ -364,8 +364,6 @@ static void mptcp_check_data_fin_ack(struct sock *sk)
 
 	/* Look for an acknowledged DATA_FIN */
 	if (mptcp_pending_data_fin_ack(sk)) {
-		mptcp_stop_timer(sk);
-
 		WRITE_ONCE(msk->snd_data_fin_enable, 0);
 
 		switch (sk->sk_state) {
@@ -2299,6 +2297,7 @@ static void mptcp_worker(struct work_struct *work)
 	if (!test_and_clear_bit(MPTCP_WORK_RTX, &msk->flags))
 		goto unlock;
 
+	__mptcp_clean_una(sk);
 	dfrag = mptcp_rtx_head(sk);
 	if (!dfrag)
 		goto unlock;

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
@@ -326,20 +326,13 @@ static inline struct mptcp_data_frag *mptcp_pending_tail(const struct sock *sk)
 	return list_last_entry(&msk->rtx_queue, struct mptcp_data_frag, list);
 }
 
-static inline struct mptcp_data_frag *mptcp_rtx_tail(const struct sock *sk)
+static inline struct mptcp_data_frag *mptcp_rtx_head(const struct sock *sk)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
 
-	if (!before64(msk->snd_nxt, READ_ONCE(msk->snd_una)))
+	if (msk->snd_una == READ_ONCE(msk->snd_nxt))
 		return NULL;
 
-	return list_last_entry(&msk->rtx_queue, struct mptcp_data_frag, list);
-}
-
-static inline struct mptcp_data_frag *mptcp_rtx_head(const struct sock *sk)
-{
-	struct mptcp_sock *msk = mptcp_sk(sk);
-
 	return list_first_entry_or_null(&msk->rtx_queue, struct mptcp_data_frag, list);
 }