Re: NULL pointer dereference in sysfs_readdir

[Michael Buesch <mb@bu3sch.de>]

On Saturday 21 October 2006 10:43, 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.
> 
> Is there reason to be worried...?

Looking through the code I was not able to locate the exact line
at which it oopses, with the above oops message.
Are you able to track down the exact pointer dereference, which causes
this? By inserting printks, perhaps.

Maybe FC changed some of the structures. I couldn't find
a used structure with an interresting member at offset 00000020, at least.

-- 
Greetings Michael.
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