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    Subject[PATCH 4.19 029/109] udp: fix race between close() and udp_abort()
    Date
    From: Paolo Abeni <pabeni@redhat.com>

    [ Upstream commit a8b897c7bcd47f4147d066e22cc01d1026d7640e ]

    Kaustubh reported and diagnosed a panic in udp_lib_lookup().
    The root cause is udp_abort() racing with close(). Both
    racing functions acquire the socket lock, but udp{v6}_destroy_sock()
    release it before performing destructive actions.

    We can't easily extend the socket lock scope to avoid the race,
    instead use the SOCK_DEAD flag to prevent udp_abort from doing
    any action when the critical race happens.

    Diagnosed-and-tested-by: Kaustubh Pandey <kapandey@codeaurora.org>
    Fixes: 5d77dca82839 ("net: diag: support SOCK_DESTROY for UDP sockets")
    Signed-off-by: Paolo Abeni <pabeni@redhat.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/ipv4/udp.c | 10 ++++++++++
    net/ipv6/udp.c | 3 +++
    2 files changed, 13 insertions(+)

    diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
    index 110af0e7dc7b..2ff9f774d446 100644
    --- a/net/ipv4/udp.c
    +++ b/net/ipv4/udp.c
    @@ -2432,6 +2432,9 @@ void udp_destroy_sock(struct sock *sk)
    {
    struct udp_sock *up = udp_sk(sk);
    bool slow = lock_sock_fast(sk);
    +
    + /* protects from races with udp_abort() */
    + sock_set_flag(sk, SOCK_DEAD);
    udp_flush_pending_frames(sk);
    unlock_sock_fast(sk, slow);
    if (static_branch_unlikely(&udp_encap_needed_key) && up->encap_type) {
    @@ -2673,10 +2676,17 @@ int udp_abort(struct sock *sk, int err)
    {
    lock_sock(sk);

    + /* udp{v6}_destroy_sock() sets it under the sk lock, avoid racing
    + * with close()
    + */
    + if (sock_flag(sk, SOCK_DEAD))
    + goto out;
    +
    sk->sk_err = err;
    sk->sk_error_report(sk);
    __udp_disconnect(sk, 0);

    +out:
    release_sock(sk);

    return 0;
    diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
    index 6799ad462be3..c4a76c6af205 100644
    --- a/net/ipv6/udp.c
    +++ b/net/ipv6/udp.c
    @@ -1476,6 +1476,9 @@ void udpv6_destroy_sock(struct sock *sk)
    {
    struct udp_sock *up = udp_sk(sk);
    lock_sock(sk);
    +
    + /* protects from races with udp_abort() */
    + sock_set_flag(sk, SOCK_DEAD);
    udp_v6_flush_pending_frames(sk);
    release_sock(sk);

    --
    2.30.2
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