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    Subject[PATCH AUTOSEL 5.4 16/26] net/packet: annotate accesses to po->bind
    Date
    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit c7d2ef5dd4b03ed0ee1d13bc0c55f9cf62d49bd6 ]

    tpacket_snd(), packet_snd(), packet_getname() and packet_seq_show()
    can read po->num without holding a lock. This means other threads
    can change po->num at the same time.

    KCSAN complained about this known fact [1]
    Add READ_ONCE()/WRITE_ONCE() to address the issue.

    [1] BUG: KCSAN: data-race in packet_do_bind / packet_sendmsg

    write to 0xffff888131a0dcc0 of 2 bytes by task 24714 on cpu 0:
    packet_do_bind+0x3ab/0x7e0 net/packet/af_packet.c:3181
    packet_bind+0xc3/0xd0 net/packet/af_packet.c:3255
    __sys_bind+0x200/0x290 net/socket.c:1637
    __do_sys_bind net/socket.c:1648 [inline]
    __se_sys_bind net/socket.c:1646 [inline]
    __x64_sys_bind+0x3d/0x50 net/socket.c:1646
    do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
    entry_SYSCALL_64_after_hwframe+0x44/0xae

    read to 0xffff888131a0dcc0 of 2 bytes by task 24719 on cpu 1:
    packet_snd net/packet/af_packet.c:2899 [inline]
    packet_sendmsg+0x317/0x3570 net/packet/af_packet.c:3040
    sock_sendmsg_nosec net/socket.c:654 [inline]
    sock_sendmsg net/socket.c:674 [inline]
    ____sys_sendmsg+0x360/0x4d0 net/socket.c:2350
    ___sys_sendmsg net/socket.c:2404 [inline]
    __sys_sendmsg+0x1ed/0x270 net/socket.c:2433
    __do_sys_sendmsg net/socket.c:2442 [inline]
    __se_sys_sendmsg net/socket.c:2440 [inline]
    __x64_sys_sendmsg+0x42/0x50 net/socket.c:2440
    do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
    entry_SYSCALL_64_after_hwframe+0x44/0xae

    value changed: 0x0000 -> 0x1200

    Reported by Kernel Concurrency Sanitizer on:
    CPU: 1 PID: 24719 Comm: syz-executor.5 Not tainted 5.13.0-rc4-syzkaller #0
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Reported-by: syzbot <syzkaller@googlegroups.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/packet/af_packet.c | 16 ++++++++--------
    1 file changed, 8 insertions(+), 8 deletions(-)

    diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
    index fbc2d4dfddf0..e582799d4e85 100644
    --- a/net/packet/af_packet.c
    +++ b/net/packet/af_packet.c
    @@ -2656,7 +2656,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
    }
    if (likely(saddr == NULL)) {
    dev = packet_cached_dev_get(po);
    - proto = po->num;
    + proto = READ_ONCE(po->num);
    } else {
    err = -EINVAL;
    if (msg->msg_namelen < sizeof(struct sockaddr_ll))
    @@ -2869,7 +2869,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)

    if (likely(saddr == NULL)) {
    dev = packet_cached_dev_get(po);
    - proto = po->num;
    + proto = READ_ONCE(po->num);
    } else {
    err = -EINVAL;
    if (msg->msg_namelen < sizeof(struct sockaddr_ll))
    @@ -3141,7 +3141,7 @@ static int packet_do_bind(struct sock *sk, const char *name, int ifindex,
    /* prevents packet_notifier() from calling
    * register_prot_hook()
    */
    - po->num = 0;
    + WRITE_ONCE(po->num, 0);
    __unregister_prot_hook(sk, true);
    rcu_read_lock();
    dev_curr = po->prot_hook.dev;
    @@ -3151,7 +3151,7 @@ static int packet_do_bind(struct sock *sk, const char *name, int ifindex,
    }

    BUG_ON(po->running);
    - po->num = proto;
    + WRITE_ONCE(po->num, proto);
    po->prot_hook.type = proto;

    if (unlikely(unlisted)) {
    @@ -3496,7 +3496,7 @@ static int packet_getname(struct socket *sock, struct sockaddr *uaddr,

    sll->sll_family = AF_PACKET;
    sll->sll_ifindex = po->ifindex;
    - sll->sll_protocol = po->num;
    + sll->sll_protocol = READ_ONCE(po->num);
    sll->sll_pkttype = 0;
    rcu_read_lock();
    dev = dev_get_by_index_rcu(sock_net(sk), po->ifindex);
    @@ -4405,7 +4405,7 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
    was_running = po->running;
    num = po->num;
    if (was_running) {
    - po->num = 0;
    + WRITE_ONCE(po->num, 0);
    __unregister_prot_hook(sk, false);
    }
    spin_unlock(&po->bind_lock);
    @@ -4440,7 +4440,7 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,

    spin_lock(&po->bind_lock);
    if (was_running) {
    - po->num = num;
    + WRITE_ONCE(po->num, num);
    register_prot_hook(sk);
    }
    spin_unlock(&po->bind_lock);
    @@ -4613,7 +4613,7 @@ static int packet_seq_show(struct seq_file *seq, void *v)
    s,
    refcount_read(&s->sk_refcnt),
    s->sk_type,
    - ntohs(po->num),
    + ntohs(READ_ONCE(po->num)),
    po->ifindex,
    po->running,
    atomic_read(&s->sk_rmem_alloc),
    --
    2.30.2
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