Re: NULL pointer dereference in sysfs_readdir

[Maneesh Soni]

On Sat, Oct 21, 2006 at 10:43:49AM +0200, Stefan Richter wrote:
> Here is a report about lockups and/or(?) oopses while HALD is obviously
> traversing sysfs files of FireWire devices, seen under Fedora Core
> kernels 2.6.{16,17,18} on an SMP setup:
> 
> https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=188140
> 
> > May 17 11:49:42 malbec kernel: Unable to handle kernel NULL pointer dereference at virtual address 00000020
> > May 17 11:49:42 malbec kernel:  printing eip:
> > May 17 11:49:42 malbec kernel: c019797d
> > May 17 11:49:42 malbec kernel: *pde = 14924001
> > May 17 11:49:42 malbec kernel: Oops: 0000 [#1]
> > May 17 11:49:42 malbec kernel: SMP 
> > May 17 11:49:42 malbec kernel: last sysfs file: /class/net/eth0/address
> > May 17 11:49:42 malbec kernel: Modules linked in: sunrpc xt_limit xt_state ip_conntrack nfnetlink xt_tcpudp iptable_filter ip_tables ip6table_filter ip6_tables x_tables ipv6 dm_multipath lp parport_pc parport floppy nvram ohci1394 ieee1394 uhci_hcd sg ohci_hcd ehci_hcd snd_emu10k1_synth snd_emux_synth snd_seq_virmidi snd_seq_midi_emul snd_emu10k1 snd_ac97_codec snd_ac97_bus snd_usb_audio snd_usb_lib snd_rawmidi snd_seq_dummy snd_seq_oss snd_seq_midi_event i2c_piix4 snd_seq i2c_core snd_pcm_oss snd_mixer_oss snd_pcm snd_seq_device snd_timer snd_page_alloc snd_util_mem emu10k1_gp snd_hwdep gameport snd soundcore e100 mii dm_snapshot dm_zero dm_mirror dm_mod ext3 jbd aic7xxx scsi_transport_spi sd_mod scsi_mod
> > May 17 11:49:42 malbec kernel: CPU:    1
> > May 17 11:49:42 malbec kernel: EIP:    0060:[<c019797d>]    Not tainted VLI
> > May 17 11:49:42 malbec kernel: EFLAGS: 00010282   (2.6.16-1.2111_FC5smp #1) 
> > May 17 11:49:42 malbec kernel: EIP is at sysfs_readdir+0x153/0x202
> > May 17 11:49:42 malbec kernel: eax: 00000000   ebx: d56cd5a0   ecx: 0000000a   edx: 00000002
> > May 17 11:49:42 malbec kernel: esi: e3a2e6fc   edi: e3a2e707   ebp: e2c08b14   esp: d55a7f50
> > May 17 11:49:42 malbec kernel: ds: 007b   es: 007b   ss: 0068
> > May 17 11:49:42 malbec kernel: Process hald (pid: 2512, threadinfo=d55a7000 task=d8bc7930)
> > May 17 11:49:42 malbec kernel: Stack: <0>c0171894 d55a7f98 d4c73e60 e3b28a4c e2c08b18 0000000a c0362f80 d4c73e60 
> > May 17 11:49:42 malbec kernel:        e3b2655c e3b265dc c0171a53 d55a7f98 c0171894 fffffff7 09e4f5d4 00000000 
> > May 17 11:49:42 malbec kernel:        d4c73e60 c0171ae0 09e4f754 09e4f73c 00000e80 ffffffea 0000000d 09e4f5d4 
> > May 17 11:49:42 malbec kernel: Call Trace:
> > May 17 11:49:42 malbec kernel:  [<c0171894>] filldir64+0x0/0xc3     [<c0171a53>] vfs_readdir+0x66/0x90
> > May 17 11:49:42 malbec kernel:  [<c0171894>] filldir64+0x0/0xc3     [<c0171ae0>] sys_getdents64+0x63/0xa5
> > May 17 11:49:42 malbec kernel:  [<c0103db9>] syscall_call+0x7/0xb    <0>Code: 14 00 0f 84 ad 00 00 00 89 e8 e8 b3 e8 ff ff 89 c6 31 c0 83 c9 ff 89 f7 f2 ae f7 d1 49 89 4c 24 14 8b 45 20 85 c0 74 08 8b 40 18 <8b> 50 20 eb 11 ba 02 00 00 00 a1 20 24 48 c0 e8 2e 06 fe ff 89 
> 
> A quick look at linux-2.6.19-rc2/fs/sysfs/dir.c::sysfs_readdir shows a
> list_move, a traversal through a list, and some accesses to data with no
> apparent protection by mutexes.
> 
Most of the sysfs locking is done by parent inode's i_mutex. And for
sysfs_readdir(), i_mutex is held at VFS layer in vfs_readdir().

If this is not happening during boot, could you please recreate the
oops with at kdump? I guess kdump should work well on FC.

(http://fedoraproject.org/wiki/FC6KdumpKexecHowTo?highlight=%28FC6KdumpKexecHowTo%29)

> Is there reason to be worried...?

Though locking looks fine to me.. but oops is a reason enough to
be worried about.

Thanks
Maneesh
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