Re: WARNING in strp_data_ready

On Wed, Dec 27, 2017 at 9:08 PM, Ozgur [off-list ref] wrote:

27.12.2017, 22:21, "Dmitry Vyukov" [off-list ref]:

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On Wed, Dec 27, 2017 at 8:09 PM, Tom Herbert [off-list ref] wrote:

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 Did you try the patch I posted?

Hi Tom,

Hello Dmitry,

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No. And I didn't know I need to. Why?
If you think the patch needs additional testing, you can ask syzbot to
test it. See https://github.com/google/syzkaller/blob/master/docs/syzbot.md#communication-with-syzbot
Otherwise proceed with committing it. Or what are we waiting for?

Thanks

I think we need to fixed patch for crash, in fact check to patch code and test solve the bug.
How do test it because there is no patch in the following bug?

Hi Ozgur,

I am not sure I completely understand what you mean. But the
reproducer for this bug (which one can use for testing) is here:
https://groups.google.com/forum/#!topic/syzkaller-bugs/Kxs05ziCpgY
Tom also mentions there is some patch for this, but I don't know where
it is, it doesn't seem to be referenced from this thread.

The fix patch should be for this net/kcm/kcmsock.c file and  lock functions must be added calling sk_data_ready ().
Regards

Ozgur

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 On Wed, Dec 27, 2017 at 10:25 AM, Dmitry Vyukov [off-list ref] wrote:

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 On Wed, Dec 6, 2017 at 4:44 PM, Dmitry Vyukov [off-list ref] wrote:

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 [off-list ref] wrote:

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 On 10/24/2017 08:20 AM, syzbot wrote:

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 Hello,

 syzkaller hit the following crash on 73d3393ada4f70fa3df5639c8d438f2f034c0ecb
 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

 WARNING: CPU: 0 PID: 2996 at ./include/net/sock.h:1505 sock_owned_by_me include/net/sock.h:1505 [inline]
 WARNING: CPU: 0 PID: 2996 at ./include/net/sock.h:1505 sock_owned_by_user include/net/sock.h:1511 [inline]
 WARNING: CPU: 0 PID: 2996 at ./include/net/sock.h:1505 strp_data_ready+0x2b7/0x390 net/strparser/strparser.c:404
 Kernel panic - not syncing: panic_on_warn set ...

 CPU: 0 PID: 2996 Comm: syzkaller142210 Not tainted 4.14.0-rc5+ #138
 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 Call Trace:
  <IRQ>
  __dump_stack lib/dump_stack.c:16 [inline]
  dump_stack+0x194/0x257 lib/dump_stack.c:52
  panic+0x1e4/0x417 kernel/panic.c:181
  __warn+0x1c4/0x1d9 kernel/panic.c:542
  report_bug+0x211/0x2d0 lib/bug.c:183
  fixup_bug+0x40/0x90 arch/x86/kernel/traps.c:178
  do_trap_no_signal arch/x86/kernel/traps.c:212 [inline]
  do_trap+0x260/0x390 arch/x86/kernel/traps.c:261
  do_error_trap+0x120/0x390 arch/x86/kernel/traps.c:298
  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:311
  invalid_op+0x18/0x20 arch/x86/entry/entry_64.S:905
 RIP: 0010:sock_owned_by_me include/net/sock.h:1505 [inline]
 RIP: 0010:sock_owned_by_user include/net/sock.h:1511 [inline]
 RIP: 0010:strp_data_ready+0x2b7/0x390 net/strparser/strparser.c:404
 RSP: 0018:ffff8801db206b18 EFLAGS: 00010206
 RAX: ffff8801d1e02080 RBX: ffff8801dad74c48 RCX: 0000000000000000
 RDX: 0000000000000100 RSI: ffff8801d29fa0a0 RDI: ffffffff85cbede0
 RBP: ffff8801db206b38 R08: 0000000000000005 R09: 1ffffffff0ce0bcd
 R10: ffff8801db206a00 R11: dffffc0000000000 R12: ffff8801d29fa000
 R13: ffff8801dad74c50 R14: ffff8801d4350a92 R15: 0000000000000001
  psock_data_ready+0x56/0x70 net/kcm/kcmsock.c:353

 Looks like KCM is calling sk_data_ready() without first taking the
 sock lock.

 /* Called with lower sock held */
 static void kcm_rcv_strparser(struct strparser *strp, struct sk_buff *skb)
 {
  [...]
         if (kcm_queue_rcv_skb(&kcm->sk, skb)) {

 In this case kcm->sk is not the same lock the comment is referring to.
 And kcm_queue_rcv_skb() will eventually call sk_data_ready().

 @Tom, how about wrapping the sk_data_ready call in {lock|release}_sock?
 I don't have anything better in mind immediately.

 The sock locks are taken in reverse order in the send path so so
 grabbing kcm sock lock with lower lock held to call sk_data_ready may
 lead to deadlock like I think.

 It might be possible to change the order in the send path to do this.
 Something like:

 trylock on lower socket lock
 -if trylock fails
   - release kcm sock lock
   - lock lower sock
   - lock kcm sock
 - call sendpage locked function

 I admit that dealing with two levels of socket locks in the data path
 is quite a pain :-)

 up

 still happening and we've lost 50K+ test VMs on this

 up

 Still happens and number of crashes crossed 60K, can we do something
 with this please?