• Eric Dumazet's avatar
    net/packet: fix a race in packet_bind() and packet_notifier() · 15fe076e
    Eric Dumazet authored
    syzbot reported crashes [1] and provided a C repro easing bug hunting.
    
    When/if packet_do_bind() calls __unregister_prot_hook() and releases
    po->bind_lock, another thread can run packet_notifier() and process an
    NETDEV_UP event.
    
    This calls register_prot_hook() and hooks again the socket right before
    first thread is able to grab again po->bind_lock.
    
    Fixes this issue by temporarily setting po->num to 0, as suggested by
    David Miller.
    
    [1]
    dev_remove_pack: ffff8801bf16fa80 not found
    ------------[ cut here ]------------
    kernel BUG at net/core/dev.c:7945!  ( BUG_ON(!list_empty(&dev->ptype_all)); )
    invalid opcode: 0000 [#1] SMP KASAN
    Dumping ftrace buffer:
       (ftrace buffer empty)
    Modules linked in:
    device syz0 entered promiscuous mode
    CPU: 0 PID: 3161 Comm: syzkaller404108 Not tainted 4.14.0+ #190
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    task: ffff8801cc57a500 task.stack: ffff8801cc588000
    RIP: 0010:netdev_run_todo+0x772/0xae0 net/core/dev.c:7945
    RSP: 0018:ffff8801cc58f598 EFLAGS: 00010293
    RAX: ffff8801cc57a500 RBX: dffffc0000000000 RCX: ffffffff841f75b2
    RDX: 0000000000000000 RSI: 1ffff100398b1ede RDI: ffff8801bf1f8810
    device syz0 entered promiscuous mode
    RBP: ffff8801cc58f898 R08: 0000000000000001 R09: 0000000000000000
    R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801bf1f8cd8
    R13: ffff8801cc58f870 R14: ffff8801bf1f8780 R15: ffff8801cc58f7f0
    FS:  0000000001716880(0000) GS:ffff8801db400000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 0000000020b13000 CR3: 0000000005e25000 CR4: 00000000001406f0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
     rtnl_unlock+0xe/0x10 net/core/rtnetlink.c:106
     tun_detach drivers/net/tun.c:670 [inline]
     tun_chr_close+0x49/0x60 drivers/net/tun.c:2845
     __fput+0x333/0x7f0 fs/file_table.c:210
     ____fput+0x15/0x20 fs/file_table.c:244
     task_work_run+0x199/0x270 kernel/task_work.c:113
     exit_task_work include/linux/task_work.h:22 [inline]
     do_exit+0x9bb/0x1ae0 kernel/exit.c:865
     do_group_exit+0x149/0x400 kernel/exit.c:968
     SYSC_exit_group kernel/exit.c:979 [inline]
     SyS_exit_group+0x1d/0x20 kernel/exit.c:977
     entry_SYSCALL_64_fastpath+0x1f/0x96
    RIP: 0033:0x44ad19
    
    Fixes: 30f7ea1c ("packet: race condition in packet_bind")
    Signed-off-by: 's avatarEric Dumazet <edumazet@google.com>
    Reported-by: 's avatarsyzbot <syzkaller@googlegroups.com>
    Cc: Francesco Ruggeri <fruggeri@aristanetworks.com>
    Signed-off-by: 's avatarDavid S. Miller <davem@davemloft.net>
    15fe076e
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