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Message-ID: <CACT4Y+bFsT4ZVvZSZvQdcKXb8n-79gy2tLB02jBm8wwp32YoAA@mail.gmail.com> Date: Wed, 27 Dec 2017 19:25:35 +0100 From: Dmitry Vyukov <dvyukov@...gle.com> To: Tom Herbert <tom@...bertland.com> Cc: John Fastabend <john.fastabend@...il.com>, syzbot <bot+c91c53af67f9ebe599a337d2e70950366153b295@...kaller.appspotmail.com>, "David S. Miller" <davem@...emloft.net>, Eric Biggers <ebiggers@...gle.com>, LKML <linux-kernel@...r.kernel.org>, Linux Kernel Network Developers <netdev@...r.kernel.org>, syzkaller-bugs@...glegroups.com, Tom Herbert <tom@...ntonium.net>, Cong Wang <xiyou.wangcong@...il.com> Subject: Re: WARNING in strp_data_ready On Wed, Dec 6, 2017 at 4:44 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote: >> <john.fastabend@...il.com> wrote: >>> 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. >>> >> 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?
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