• Craig Gallek's avatar
    dsa: fix flow disector null pointer · 7324157b
    Craig Gallek authored
    A recent change to fix up DSA device behavior made the assumption that
    all skbs passing through the flow disector will be associated with a
    device. This does not appear to be a safe assumption.  Syzkaller found
    the crash below by attaching a BPF socket filter that tries to find the
    payload offset of a packet passing between two unix sockets.
    
    kasan: GPF could be caused by NULL-ptr deref or user memory access
    general protection fault: 0000 [#1] SMP KASAN
    Dumping ftrace buffer:
       (ftrace buffer empty)
    Modules linked in:
    CPU: 0 PID: 2940 Comm: syzkaller872007 Not tainted 4.13.0-rc4-next-20170811 #1
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    task: ffff8801d1b425c0 task.stack: ffff8801d0bc0000
    RIP: 0010:__skb_flow_dissect+0xdcd/0x3ae0 net/core/flow_dissector.c:445
    RSP: 0018:ffff8801d0bc7340 EFLAGS: 00010206
    RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
    RDX: 0000000000000060 RSI: ffffffff856dc080 RDI: 0000000000000300
    RBP: ffff8801d0bc7870 R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000000000008 R11: ffffed003a178f1e R12: 0000000000000000
    R13: 0000000000000000 R14: ffffffff856dc080 R15: ffff8801ce223140
    FS:  00000000016ed880(0000) GS:ffff8801dc000000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 0000000020008000 CR3: 00000001ce22d000 CR4: 00000000001406f0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
     skb_flow_dissect_flow_keys include/linux/skbuff.h:1176 [inline]
     skb_get_poff+0x9a/0x1a0 net/core/flow_dissector.c:1079
     ______skb_get_pay_offset net/core/filter.c:114 [inline]
     __skb_get_pay_offset+0x15/0x20 net/core/filter.c:112
    Code: 80 3c 02 00 44 89 6d 10 0f 85 44 2b 00 00 4d 8b 67 20 48 b8 00 00 00 00 00 fc ff df 49 8d bc 24 00 03 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 13 2b 00 00 4d 8b a4 24 00 03 00 00 4d 85 e4
    RIP: __skb_flow_dissect+0xdcd/0x3ae0 net/core/flow_dissector.c:445 RSP: ffff8801d0bc7340
    
    Fixes: 43e66528 ("net-next: dsa: fix flow dissection")
    Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
    Signed-off-by: default avatarCraig Gallek <kraig@google.com>
    Reviewed-by: default avatarAndrew Lunn <andrew@lunn.ch>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    7324157b
flow_dissector.c 31.5 KB