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    Subject[PATCH 4.4 028/108] net: igmp: add a missing rcu locking section
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Eric Dumazet <edumazet@google.com>


    [ Upstream commit e7aadb27a5415e8125834b84a74477bfbee4eff5 ]

    Newly added igmpv3_get_srcaddr() needs to be called under rcu lock.

    Timer callbacks do not ensure this locking.

    =============================
    WARNING: suspicious RCU usage
    4.15.0+ #200 Not tainted
    -----------------------------
    ./include/linux/inetdevice.h:216 suspicious rcu_dereference_check() usage!

    other info that might help us debug this:

    rcu_scheduler_active = 2, debug_locks = 1
    3 locks held by syzkaller616973/4074:
    #0: (&mm->mmap_sem){++++}, at: [<00000000bfce669e>] __do_page_fault+0x32d/0xc90 arch/x86/mm/fault.c:1355
    #1: ((&im->timer)){+.-.}, at: [<00000000619d2f71>] lockdep_copy_map include/linux/lockdep.h:178 [inline]
    #1: ((&im->timer)){+.-.}, at: [<00000000619d2f71>] call_timer_fn+0x1c6/0x820 kernel/time/timer.c:1316
    #2: (&(&im->lock)->rlock){+.-.}, at: [<000000005f833c5c>] spin_lock_bh include/linux/spinlock.h:315 [inline]
    #2: (&(&im->lock)->rlock){+.-.}, at: [<000000005f833c5c>] igmpv3_send_report+0x98/0x5b0 net/ipv4/igmp.c:600

    stack backtrace:
    CPU: 0 PID: 4074 Comm: syzkaller616973 Not tainted 4.15.0+ #200
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    Call Trace:
    <IRQ>
    __dump_stack lib/dump_stack.c:17 [inline]
    dump_stack+0x194/0x257 lib/dump_stack.c:53
    lockdep_rcu_suspicious+0x123/0x170 kernel/locking/lockdep.c:4592
    __in_dev_get_rcu include/linux/inetdevice.h:216 [inline]
    igmpv3_get_srcaddr net/ipv4/igmp.c:329 [inline]
    igmpv3_newpack+0xeef/0x12e0 net/ipv4/igmp.c:389
    add_grhead.isra.27+0x235/0x300 net/ipv4/igmp.c:432
    add_grec+0xbd3/0x1170 net/ipv4/igmp.c:565
    igmpv3_send_report+0xd5/0x5b0 net/ipv4/igmp.c:605
    igmp_send_report+0xc43/0x1050 net/ipv4/igmp.c:722
    igmp_timer_expire+0x322/0x5c0 net/ipv4/igmp.c:831
    call_timer_fn+0x228/0x820 kernel/time/timer.c:1326
    expire_timers kernel/time/timer.c:1363 [inline]
    __run_timers+0x7ee/0xb70 kernel/time/timer.c:1666
    run_timer_softirq+0x4c/0x70 kernel/time/timer.c:1692
    __do_softirq+0x2d7/0xb85 kernel/softirq.c:285
    invoke_softirq kernel/softirq.c:365 [inline]
    irq_exit+0x1cc/0x200 kernel/softirq.c:405
    exiting_irq arch/x86/include/asm/apic.h:541 [inline]
    smp_apic_timer_interrupt+0x16b/0x700 arch/x86/kernel/apic/apic.c:1052
    apic_timer_interrupt+0xa9/0xb0 arch/x86/entry/entry_64.S:938

    Fixes: a46182b00290 ("net: igmp: Use correct source address on IGMPv3 reports")
    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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv4/igmp.c | 4 ++++
    1 file changed, 4 insertions(+)

    --- a/net/ipv4/igmp.c
    +++ b/net/ipv4/igmp.c
    @@ -392,7 +392,11 @@ static struct sk_buff *igmpv3_newpack(st
    pip->frag_off = htons(IP_DF);
    pip->ttl = 1;
    pip->daddr = fl4.daddr;
    +
    + rcu_read_lock();
    pip->saddr = igmpv3_get_srcaddr(dev, &fl4);
    + rcu_read_unlock();
    +
    pip->protocol = IPPROTO_IGMP;
    pip->tot_len = 0; /* filled in later */
    ip_select_ident(net, skb, NULL);

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