[PATCH 5.14 139/151] mptcp: fix possible stall on recvmsg()

Greg Kroah-Hartman
2021-10-18T14:03:50Z

From: Paolo Abeni <pabeni@redhat.com>

commit 612f71d7328c14369924384ad2170aae2a6abd92 upstream.

recvmsg() can enter an infinite loop if the caller provides the
MSG_WAITALL, the data present in the receive queue is not sufficient to
fulfill the request, and no more data is received by the peer.

When the above happens, mptcp_wait_data() will always return with
no wait, as the MPTCP_DATA_READY flag checked by such function is
set and never cleared in such code path.

Leveraging the above syzbot was able to trigger an RCU stall:

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 0-...!: (10499 ticks this GP) idle=0af/1/0x4000000000000000 softirq=10678/10678 fqs=1
(t=10500 jiffies g=13089 q=109)
rcu: rcu_preempt kthread starved for 10497 jiffies! g13089 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt state:R running task stack:28696 pid: 14 ppid: 2 flags:0x00004000
Call Trace:
context_switch kernel/sched/core.c:4955 [inline]
__schedule+0x940/0x26f0 kernel/sched/core.c:6236
schedule+0xd3/0x270 kernel/sched/core.c:6315
schedule_timeout+0x14a/0x2a0 kernel/time/timer.c:1881
rcu_gp_fqs_loop+0x186/0x810 kernel/rcu/tree.c:1955
rcu_gp_kthread+0x1de/0x320 kernel/rcu/tree.c:2128
kthread+0x405/0x4f0 kernel/kthread.c:327
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 8510 Comm: syz-executor827 Not tainted 5.15.0-rc2-next-20210920-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:bytes_is_nonzero mm/kasan/generic.c:84 [inline]
RIP: 0010:memory_is_nonzero mm/kasan/generic.c:102 [inline]
RIP: 0010:memory_is_poisoned_n mm/kasan/generic.c:128 [inline]
RIP: 0010:memory_is_poisoned mm/kasan/generic.c:159 [inline]
RIP: 0010:check_region_inline mm/kasan/generic.c:180 [inline]
RIP: 0010:kasan_check_range+0xc8/0x180 mm/kasan/generic.c:189
Code: 38 00 74 ed 48 8d 50 08 eb 09 48 83 c0 01 48 39 d0 74 7a 80 38 00 74 f2 48 89 c2 b8 01 00 00 00 48 85 d2 75 56 5b 5d 41 5c c3 <48> 85 d2 74 5e 48 01 ea eb 09 48 83 c0 01 48 39 d0 74 50 80 38 00
RSP: 0018:ffffc9000cd676c8 EFLAGS: 00000283
RAX: ffffed100e9a110e RBX: ffffed100e9a110f RCX: ffffffff88ea062a
RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff888074d08870
RBP: ffffed100e9a110e R08: 0000000000000001 R09: ffff888074d08877
R10: ffffed100e9a110e R11: 0000000000000000 R12: ffff888074d08000
R13: ffff888074d08000 R14: ffff888074d08088 R15: ffff888074d08000
FS: 0000555556d8e300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
S: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000180 CR3: 0000000068909000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
test_and_clear_bit include/asm-generic/bitops/instrumented-atomic.h:83 [inline]
mptcp_release_cb+0x14a/0x210 net/mptcp/protocol.c:3016
release_sock+0xb4/0x1b0 net/core/sock.c:3204
mptcp_wait_data net/mptcp/protocol.c:1770 [inline]
mptcp_recvmsg+0xfd1/0x27b0 net/mptcp/protocol.c:2080
inet6_recvmsg+0x11b/0x5e0 net/ipv6/af_inet6.c:659
sock_recvmsg_nosec net/socket.c:944 [inline]
____sys_recvmsg+0x527/0x600 net/socket.c:2626
___sys_recvmsg+0x127/0x200 net/socket.c:2670
do_recvmmsg+0x24d/0x6d0 net/socket.c:2764
__sys_recvmmsg net/socket.c:2843 [inline]
__do_sys_recvmmsg net/socket.c:2866 [inline]
__se_sys_recvmmsg net/socket.c:2859 [inline]
__x64_sys_recvmmsg+0x20b/0x260 net/socket.c:2859
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7fc200d2dc39
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc5758e5a8 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fc200d2dc39
RDX: 0000000000000002 RSI: 00000000200017c0 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000f0b5ff
R10: 0000000000000100 R11: 0000000000000246 R12: 0000000000000003
R13: 00007ffc5758e5d0 R14: 00007ffc5758e5c0 R15: 0000000000000003

Fix the issue by replacing the MPTCP_DATA_READY bit with direct
inspection of the msk receive queue.

Reported-and-tested-by: syzbot+3360da629681aa0d22fe@syzkaller.appspotmail.com
Fixes: 7a6a6cbc3e59 ("mptcp: recvmsg() can drain data from multiple subflow")
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/mptcp/protocol.c | 55 +++++++++++++--------------------------------------
1 file changed, 15 insertions(+), 40 deletions(-)

--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -515,7 +515,6 @@ static bool mptcp_check_data_fin(struct

sk->sk_shutdown |= RCV_SHUTDOWN;
smp_mb__before_atomic(); /* SHUTDOWN must be visible first */
- set_bit(MPTCP_DATA_READY, &msk->flags);

switch (sk->sk_state) {
case TCP_ESTABLISHED:
@@ -730,10 +729,9 @@ void mptcp_data_ready(struct sock *sk, s

/* Wake-up the reader only for in-sequence data */
mptcp_data_lock(sk);
- if (move_skbs_to_msk(msk, ssk)) {
- set_bit(MPTCP_DATA_READY, &msk->flags);
+ if (move_skbs_to_msk(msk, ssk))
sk->sk_data_ready(sk);
- }
+
mptcp_data_unlock(sk);
}

@@ -838,7 +836,6 @@ static void mptcp_check_for_eof(struct m
sk->sk_shutdown |= RCV_SHUTDOWN;

smp_mb__before_atomic(); /* SHUTDOWN must be visible first */
- set_bit(MPTCP_DATA_READY, &msk->flags);
sk->sk_data_ready(sk);
}

@@ -1701,21 +1698,6 @@ out:
return copied ? : ret;
}

-static void mptcp_wait_data(struct sock *sk, long *timeo)
-{
- DEFINE_WAIT_FUNC(wait, woken_wake_function);
- struct mptcp_sock *msk = mptcp_sk(sk);
-
- add_wait_queue(sk_sleep(sk), &wait);
- sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);
-
- sk_wait_event(sk, timeo,
- test_bit(MPTCP_DATA_READY, &msk->flags), &wait);
-
- sk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk);
- remove_wait_queue(sk_sleep(sk), &wait);
-}
-
static int __mptcp_recvmsg_mskq(struct mptcp_sock *msk,
struct msghdr *msg,
size_t len, int flags,
@@ -2019,19 +2001,7 @@ static int mptcp_recvmsg(struct sock *sk
}

pr_debug("block timeout %ld", timeo);
- mptcp_wait_data(sk, &timeo);
- }
-
- if (skb_queue_empty_lockless(&sk->sk_receive_queue) &&
- skb_queue_empty(&msk->receive_queue)) {
- /* entire backlog drained, clear DATA_READY. */
- clear_bit(MPTCP_DATA_READY, &msk->flags);
-
- /* .. race-breaker: ssk might have gotten new data
- * after last __mptcp_move_skbs() returned false.
- */
- if (unlikely(__mptcp_move_skbs(msk)))
- set_bit(MPTCP_DATA_READY, &msk->flags);
+ sk_wait_data(sk, &timeo, NULL);
}

out_err:
@@ -2040,9 +2010,9 @@ out_err:
tcp_recv_timestamp(msg, sk, &tss);
}

- pr_debug("msk=%p data_ready=%d rx queue empty=%d copied=%d",
- msk, test_bit(MPTCP_DATA_READY, &msk->flags),
- skb_queue_empty_lockless(&sk->sk_receive_queue), copied);
+ pr_debug("msk=%p rx queue empty=%d:%d copied=%d",
+ msk, skb_queue_empty_lockless(&sk->sk_receive_queue),
+ skb_queue_empty(&msk->receive_queue), copied);
if (!(flags & MSG_PEEK))
mptcp_rcv_space_adjust(msk, copied);

@@ -2255,7 +2225,6 @@ static void mptcp_check_fastclose(struct
inet_sk_state_store(sk, TCP_CLOSE);
sk->sk_shutdown = SHUTDOWN_MASK;
smp_mb__before_atomic(); /* SHUTDOWN must be visible first */
- set_bit(MPTCP_DATA_READY, &msk->flags);
set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags);

mptcp_close_wake_up(sk);
@@ -3272,8 +3241,14 @@ unlock_fail:

static __poll_t mptcp_check_readable(struct mptcp_sock *msk)
{
- return test_bit(MPTCP_DATA_READY, &msk->flags) ? EPOLLIN | EPOLLRDNORM :
- 0;
+ /* Concurrent splices from sk_receive_queue into receive_queue will
+ * always show at least one non-empty queue when checked in this order.
+ */
+ if (skb_queue_empty_lockless(&((struct sock *)msk)->sk_receive_queue) &&
+ skb_queue_empty_lockless(&msk->receive_queue))
+ return 0;
+
+ return EPOLLIN | EPOLLRDNORM;
}

static __poll_t mptcp_check_writeable(struct mptcp_sock *msk)
@@ -3308,7 +3283,7 @@ static __poll_t mptcp_poll(struct file *
state = inet_sk_state_load(sk);
pr_debug("msk=%p state=%d flags=%lx", msk, state, msk->flags);
if (state == TCP_LISTEN)
- return mptcp_check_readable(msk);
+ return test_bit(MPTCP_DATA_READY, &msk->flags) ? EPOLLIN | EPOLLRDNORM : 0;

if (state != TCP_SYN_SENT && state != TCP_SYN_RECV) {
mask |= mptcp_check_readable(msk);