Re: WARNING in strp_data_ready

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

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.

Thanks,
John