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    • E
      ipv6: flowlabel: do not leave opt->tot_len with garbage · 864e2a1f
      Eric Dumazet 提交于
      When syzkaller team brought us a C repro for the crash [1] that
      had been reported many times in the past, I finally could find
      the root cause.
      
      If FlowLabel info is merged by fl6_merge_options(), we leave
      part of the opt_space storage provided by udp/raw/l2tp with random value
      in opt_space.tot_len, unless a control message was provided at sendmsg()
      time.
      
      Then ip6_setup_cork() would use this random value to perform a kzalloc()
      call. Undefined behavior and crashes.
      
      Fix is to properly set tot_len in fl6_merge_options()
      
      At the same time, we can also avoid consuming memory and cpu cycles
      to clear it, if every option is copied via a kmemdup(). This is the
      change in ip6_setup_cork().
      
      [1]
      kasan: CONFIG_KASAN_INLINE enabled
      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: 6613 Comm: syz-executor0 Not tainted 4.14.0-rc4+ #127
      Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
      task: ffff8801cb64a100 task.stack: ffff8801cc350000
      RIP: 0010:ip6_setup_cork+0x274/0x15c0 net/ipv6/ip6_output.c:1168
      RSP: 0018:ffff8801cc357550 EFLAGS: 00010203
      RAX: dffffc0000000000 RBX: ffff8801cc357748 RCX: 0000000000000010
      RDX: 0000000000000002 RSI: ffffffff842bd1d9 RDI: 0000000000000014
      RBP: ffff8801cc357620 R08: ffff8801cb17f380 R09: ffff8801cc357b10
      R10: ffff8801cb64a100 R11: 0000000000000000 R12: ffff8801cc357ab0
      R13: ffff8801cc357b10 R14: 0000000000000000 R15: ffff8801c3bbf0c0
      FS:  00007f9c5c459700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: 0000000020324000 CR3: 00000001d1cf2000 CR4: 00000000001406f0
      DR0: 0000000020001010 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
      Call Trace:
       ip6_make_skb+0x282/0x530 net/ipv6/ip6_output.c:1729
       udpv6_sendmsg+0x2769/0x3380 net/ipv6/udp.c:1340
       inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:762
       sock_sendmsg_nosec net/socket.c:633 [inline]
       sock_sendmsg+0xca/0x110 net/socket.c:643
       SYSC_sendto+0x358/0x5a0 net/socket.c:1750
       SyS_sendto+0x40/0x50 net/socket.c:1718
       entry_SYSCALL_64_fastpath+0x1f/0xbe
      RIP: 0033:0x4520a9
      RSP: 002b:00007f9c5c458c08 EFLAGS: 00000216 ORIG_RAX: 000000000000002c
      RAX: ffffffffffffffda RBX: 0000000000718000 RCX: 00000000004520a9
      RDX: 0000000000000001 RSI: 0000000020fd1000 RDI: 0000000000000016
      RBP: 0000000000000086 R08: 0000000020e0afe4 R09: 000000000000001c
      R10: 0000000000000000 R11: 0000000000000216 R12: 00000000004bb1ee
      R13: 00000000ffffffff R14: 0000000000000016 R15: 0000000000000029
      Code: e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 ea 0f 00 00 48 8d 79 04 48 b8 00 00 00 00 00 fc ff df 45 8b 74 24 04 48 89 fa 48 c1 ea 03 <0f> b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85
      RIP: ip6_setup_cork+0x274/0x15c0 net/ipv6/ip6_output.c:1168 RSP: ffff8801cc357550
      Signed-off-by: NEric Dumazet <edumazet@google.com>
      Reported-by: NDmitry Vyukov <dvyukov@google.com>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      864e2a1f
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