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    Subject[PATCH 4.19 190/229] net: If sock is dead dont access socks sk_wq in sk_stream_wait_memory
    Date
    From: Liu Jian <liujian56@huawei.com>

    [ Upstream commit 3f8ef65af927db247418d4e1db49164d7a158fc5 ]

    Fixes the below NULL pointer dereference:

    [...]
    [ 14.471200] Call Trace:
    [ 14.471562] <TASK>
    [ 14.471882] lock_acquire+0x245/0x2e0
    [ 14.472416] ? remove_wait_queue+0x12/0x50
    [ 14.473014] ? _raw_spin_lock_irqsave+0x17/0x50
    [ 14.473681] _raw_spin_lock_irqsave+0x3d/0x50
    [ 14.474318] ? remove_wait_queue+0x12/0x50
    [ 14.474907] remove_wait_queue+0x12/0x50
    [ 14.475480] sk_stream_wait_memory+0x20d/0x340
    [ 14.476127] ? do_wait_intr_irq+0x80/0x80
    [ 14.476704] do_tcp_sendpages+0x287/0x600
    [ 14.477283] tcp_bpf_push+0xab/0x260
    [ 14.477817] tcp_bpf_sendmsg_redir+0x297/0x500
    [ 14.478461] ? __local_bh_enable_ip+0x77/0xe0
    [ 14.479096] tcp_bpf_send_verdict+0x105/0x470
    [ 14.479729] tcp_bpf_sendmsg+0x318/0x4f0
    [ 14.480311] sock_sendmsg+0x2d/0x40
    [ 14.480822] ____sys_sendmsg+0x1b4/0x1c0
    [ 14.481390] ? copy_msghdr_from_user+0x62/0x80
    [ 14.482048] ___sys_sendmsg+0x78/0xb0
    [ 14.482580] ? vmf_insert_pfn_prot+0x91/0x150
    [ 14.483215] ? __do_fault+0x2a/0x1a0
    [ 14.483738] ? do_fault+0x15e/0x5d0
    [ 14.484246] ? __handle_mm_fault+0x56b/0x1040
    [ 14.484874] ? lock_is_held_type+0xdf/0x130
    [ 14.485474] ? find_held_lock+0x2d/0x90
    [ 14.486046] ? __sys_sendmsg+0x41/0x70
    [ 14.486587] __sys_sendmsg+0x41/0x70
    [ 14.487105] ? intel_pmu_drain_pebs_core+0x350/0x350
    [ 14.487822] do_syscall_64+0x34/0x80
    [ 14.488345] entry_SYSCALL_64_after_hwframe+0x63/0xcd
    [...]

    The test scenario has the following flow:

    thread1 thread2
    ----------- ---------------
    tcp_bpf_sendmsg
    tcp_bpf_send_verdict
    tcp_bpf_sendmsg_redir sock_close
    tcp_bpf_push_locked __sock_release
    tcp_bpf_push //inet_release
    do_tcp_sendpages sock->ops->release
    sk_stream_wait_memory // tcp_close
    sk_wait_event sk->sk_prot->close
    release_sock(__sk);
    ***
    lock_sock(sk);
    __tcp_close
    sock_orphan(sk)
    sk->sk_wq = NULL
    release_sock
    ****
    lock_sock(__sk);
    remove_wait_queue(sk_sleep(sk), &wait);
    sk_sleep(sk)
    //NULL pointer dereference
    &rcu_dereference_raw(sk->sk_wq)->wait

    While waiting for memory in thread1, the socket is released with its wait
    queue because thread2 has closed it. This caused by tcp_bpf_send_verdict
    didn't increase the f_count of psock->sk_redir->sk_socket->file in thread1.

    We should check if SOCK_DEAD flag is set on wakeup in sk_stream_wait_memory
    before accessing the wait queue.

    Suggested-by: Jakub Sitnicki <jakub@cloudflare.com>
    Signed-off-by: Liu Jian <liujian56@huawei.com>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Acked-by: John Fastabend <john.fastabend@gmail.com>
    Cc: Eric Dumazet <edumazet@google.com>
    Link: https://lore.kernel.org/bpf/20220823133755.314697-2-liujian56@huawei.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/core/stream.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/net/core/stream.c b/net/core/stream.c
    index 3d98774cf128..7b411a91a81c 100644
    --- a/net/core/stream.c
    +++ b/net/core/stream.c
    @@ -159,7 +159,8 @@ int sk_stream_wait_memory(struct sock *sk, long *timeo_p)
    *timeo_p = current_timeo;
    }
    out:
    - remove_wait_queue(sk_sleep(sk), &wait);
    + if (!sock_flag(sk, SOCK_DEAD))
    + remove_wait_queue(sk_sleep(sk), &wait);
    return err;

    do_error:
    --
    2.35.1


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