Re: WARNING in netlink_ack (2)

[Xin Long]

On Thu, Jan 11, 2018 at 1:31 AM, syzbot
<syzbot+315fa6766d0f7c359327@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> Hello,
>
> syzkaller hit the following crash on
> cf1fb158230edce8a0482bfb2e59b9c390477fb6
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> C reproducer is attached
> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> for information about syzkaller reproducers
>
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+315fa6766d0f7c359327@xxxxxxxxxxxxxxxxxxxxxxxxx
> It will help syzbot understand when the bug is fixed. See footer for
> details.
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> audit: type=1400 audit(1515595879.379:7): avc:  denied  { map } for
> pid=3498 comm="syzkaller002174" path="/root/syzkaller002174137" dev="sda1"
> ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
> tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
> tc_ctl_action: received NO action attribs
> WARNING: CPU: 0 PID: 3498 at net/netlink/af_netlink.c:2365
> netlink_ack+0x625/0xa10 net/netlink/af_netlink.c:2363
> Kernel panic - not syncing: panic_on_warn set ...

shoudn't the extack be cleared after the ack for one msg ?

@@ -2443,8 +2457,10 @@ int netlink_rcv_skb(struct sk_buff *skb, int
(*cb)(struct sk_buff *,
                        goto skip;

 ack:
-               if (nlh->nlmsg_flags & NLM_F_ACK || err)
+               if (nlh->nlmsg_flags & NLM_F_ACK || err) {
                        netlink_ack(skb, nlh, err, &extack);
+                       memset(&extack, 0, sizeof(extack));
+               }

or just move the extack definition into the loop:

@@ -2417,11 +2431,11 @@ int netlink_rcv_skb(struct sk_buff *skb, int
(*cb)(struct sk_buff *,
                                                   struct nlmsghdr *,
                                                   struct netlink_ext_ack *))
 {
-       struct netlink_ext_ack extack = {};
        struct nlmsghdr *nlh;
        int err;

        while (skb->len >= nlmsg_total_size(0)) {
+               struct netlink_ext_ack extack = {};
                int msglen;



>
> CPU: 0 PID: 3498 Comm: syzkaller002174 Not tainted 4.15.0-rc7+ #256
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:17 [inline]
>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>  panic+0x1e4/0x41c kernel/panic.c:183
>  __warn+0x1dc/0x200 kernel/panic.c:547
>  report_bug+0x211/0x2d0 lib/bug.c:184
>  fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178
>  fixup_bug arch/x86/kernel/traps.c:247 [inline]
>  do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
>  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
>  invalid_op+0x22/0x40 arch/x86/entry/entry_64.S:1079
> RIP: 0010:netlink_ack+0x625/0xa10 net/netlink/af_netlink.c:2363
> RSP: 0018:ffff8801bfd8f790 EFLAGS: 00010293
> RAX: ffff8801c00560c0 RBX: ffff8801d404dc00 RCX: ffffffff8455ad75
> RDX: 0000000000000000 RSI: ffff8801c03a3530 RDI: ffff8801d404dcd8
> RBP: ffff8801bfd8f848 R08: ffffed0038e8f55d R09: ffffed0038e8f55d
> R10: 0000000000000003 R11: ffffed0038e8f55c R12: ffff8801c03a3500
> R13: ffff8801c747aac0 R14: ffff8801d404d980 R15: 1ffff10037fb1ef8
>  netlink_rcv_skb+0x375/0x470 net/netlink/af_netlink.c:2414
>  rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:4423
>  netlink_unicast_kernel net/netlink/af_netlink.c:1275 [inline]
>  netlink_unicast+0x4ee/0x700 net/netlink/af_netlink.c:1301
>  netlink_sendmsg+0xa4a/0xe60 net/netlink/af_netlink.c:1864
>  sock_sendmsg_nosec net/socket.c:636 [inline]
>  sock_sendmsg+0xca/0x110 net/socket.c:646
>  ___sys_sendmsg+0x767/0x8b0 net/socket.c:2026
>  __sys_sendmsg+0xe5/0x210 net/socket.c:2060
>  SYSC_sendmsg net/socket.c:2071 [inline]
>  SyS_sendmsg+0x2d/0x50 net/socket.c:2067
>  entry_SYSCALL_64_fastpath+0x23/0x9a
> RIP: 0033:0x440c39
> RSP: 002b:00007ffeab2f1f98 EFLAGS: 00000217 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440c39
> RDX: 0000000000008800 RSI: 00000000201dcfc8 RDI: 0000000000000003
> RBP: 00000000006cb018 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000004 R11: 0000000000000217 R12: 00000000004025a0
> R13: 0000000000402630 R14: 0000000000000000 R15: 0000000000000000
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
>
>
> ---
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