linux-kernel - Re: BUG in skb_dequeue (skb->next is NULL) (was: Re: Kernel crash with 2.6.36)

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Date:	Wed, 01 Dec 2010 11:28:19 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Simon Schubert <2@...c.org>
Cc:	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>
Subject: Re: BUG in skb_dequeue (skb->next is NULL) (was: Re: Kernel crash
 with 2.6.36)

Le mercredi 01 décembre 2010 à 09:02 +0000, Simon Schubert a écrit :
> Frédéric L. W. Meunier <2 <at> pervalidus.net> writes:

CC netdev

> 
> > Nov  7 16:21:23 pervalidus kernel: BUG: unable to handle kernel NULL pointer 
> dereference at (null)
> 
> I can confirm the bug reported by Frederic.  The culprit is at:
> 
>         next->prev = prev;
> 
> in __skb_unlink().
> 
> Something must be putting NULL pointers in the skb list.
> 
> Let me know how I can be of further help.
> 
> 
> BUG: unable to handle kernel NULL pointer dereference at (null)
> IP: [<ffffffff81459069>] skb_dequeue+0x59/0x90
> PGD 208379067 PUD 20a523067 PMD 0 
> Oops: 0002 [#1] SMP 
> last sysfs file: /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq
> CPU 1 
> Modules linked in: binfmt_misc kvm_intel kvm ipt_MASQUERADE iptable_nat nf_nat 
> xfrm_user nf_conntrack_ipv4 xfrm4_tunnel tunnel4 nf_conntrack ipcomp xfrm_ipcomp 
> esp4 ah4 nf_defrag_ipv4 xt_TCPMSS xt_tcpmss xt_tcpudp iptable_mangle deflate 
> ip_tables zlib_deflate ctr x_tables twofish_generic twofish_x86_64 
> twofish_common camellia serpent blowfish cast5 des_generic xcbc rmd160 
> sha512_generic sha1_generic crypto_null af_key pppoe pppox xfs exportfs 
> snd_hda_codec_via snd_hda_intel snd_hda_codec snd_hwdep snd_pcm_oss 
> snd_mixer_oss snd_pcm snd_seq_dummy snd_seq_oss snd_seq_midi snd_rawmidi 
> snd_seq_midi_event snd_seq snd_timer ftdi_sio snd_seq_device usbserial hwmon_vid 
> coretemp snd lp tpm_tis ppdev tpm parport_pc asus_atk0110 tpm_bios parport 
> soundcore snd_page_alloc sha256_generic cryptd aes_x86_64 aes_generic dm_crypt 
> raid10 raid1 raid0 multipath linear raid456 async_pq async_xor xor async_memcpy 
> async_raid6_recov raid6_pq async_tx fbcon tileblit font bitblit softcursor usb
> 
> Pid: 2229, comm: pulseaudio Not tainted 2.6.36 #10 P5Q-VM DO/System Product Name
> RIP: 0010:[<ffffffff81459069>]  [<ffffffff81459069>] skb_dequeue+0x59/0x90
> RSP: 0018:ffff880221927a78  EFLAGS: 00010097
> RAX: 0000000000000282 RBX: ffff88017a6d5e14 RCX: ffff88022236d200
> RDX: 0000000000000000 RSI: 0000000000000282 RDI: ffff88017a6d5e14
> RBP: ffff880221927a98 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000293 R12: ffff88022236d200
> R13: ffff88017a6d5e00 R14: 0000000000000000 R15: 0000000000000000
> FS:  00007fedd4d9f740(0000) GS:ffff880001e80000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> CR2: 0000000000000000 CR3: 000000020837a000 CR4: 00000000000006e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Process pulseaudio (pid: 2229, threadinfo ffff880221926000, task 
> ffff8802210096d0)
> Stack:
>  ffff88022236d200 ffff88022236d228 ffff88022236d200 ffff880221927f18
> <0> ffff880221927be8 ffffffff814ef0fa ffff880221927e4c ffff880221927eb4
> <0> 0000000000000040 ffff8802210096d0 ffff8802210096d0 ffff88017a6d5ea4
> Call Trace:
>  [<ffffffff814ef0fa>] unix_stream_recvmsg+0x1aa/0x790
>  [<ffffffff8145124d>] sock_recvmsg+0xfd/0x130
>  [<ffffffff81155fd0>] ? pollwake+0x0/0x60
>  [<ffffffff81452b54>] __sys_recvmsg+0x144/0x2e0
>  [<ffffffff81155fd0>] ? pollwake+0x0/0x60
>  [<ffffffff8104d88a>] ? finish_task_switch+0x4a/0xd0
>  [<ffffffff8154fa91>] ? schedule+0x411/0xa50
>  [<ffffffff81452f99>] sys_recvmsg+0x49/0x80
>  [<ffffffff8100b0b2>] system_call_fastpath+0x16/0x1b
> Code: e5 74 4f 4d 85 e4 74 26 41 83 6d 10 01 49 8b 0c 24 49 8b 54 24 08 49 c7 04 
> 24 00 00 00 00 49 c7 44 24 08 00 00 00 00 48 89 51 08 <48> 89 0a 48 89 c6 48 89 
> df e8 39 93 0f 00 4c 89 e0 48 8b 5d e8 
> RIP  [<ffffffff81459069>] skb_dequeue+0x59/0x90
>  RSP <ffff880221927a78>
> CR2: 0000000000000000
> ---[ end trace d4be3de9fdd70935 ]---
> 
> cheers
>   simon
> 
> 

Is it reproductible ?

On previous kernel (say 2.6.35) you never hit this bug ?



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