[OOPS & PATCH 2.4.18] NULL pointer dereference in ide.c,

[Paul Clements]

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Looking back at LKML archives, I think this issue was reported by someone back in
November 01, and I just saw the same issue on a system a few days ago. I think I
have tracked down the cause of the oops. I looked to see if it had been fixed in
2.4.19-pre8 and it had not, so I have attached a patch against 2.4.18. Please apply.

The kernel oops was this:

----

May  3 23:20:07 liono kernel: hda: ATAPI 32X CD-ROM drive, 256kB Cache, UDMA(33)
May  3 23:20:07 liono kernel: Uniform CD-ROM driver Revision: 3.12
May  3 23:20:07 liono kernel: hda: ide_cdrom_setup failed to register device with the cdrom driver.
May  3 23:20:07 liono kernel: Unable to handle kernel NULL pointer dereference at virtual address 00000028
May  3 23:20:07 liono kernel:  printing eip:
May  3 23:20:07 liono kernel: c019b54a
May  3 23:20:07 liono kernel: *pde = 00000000
May  3 23:20:07 liono kernel: Oops: 0000
May  3 23:20:07 liono kernel: CPU:    0
May  3 23:20:07 liono kernel: EIP:    0010:[ide_revalidate_disk+250/304]    Not tainted
May  3 23:20:07 liono kernel: EIP:    0010:[<c019b54a>]    Not tainted
May  3 23:20:07 liono kernel: EFLAGS: 00010212
May  3 23:20:07 liono kernel: EIP is at ide_revalidate_disk [kernel] 0xfa
May  3 23:20:07 liono kernel: eax: 00000000   ebx: 00000300   ecx: 00000000   edx: 00000000
May  3 23:20:07 liono kernel: esi: c03bdba0   edi: 00001100   ebp: 00000040   esp: c90e3ee0
May  3 23:20:07 liono kernel: ds: 0018   es: 0018   ss: 0018
May  3 23:20:07 liono kernel: Process modprobe (pid: 2028, stackpage=c90e3000)
May  3 23:20:07 liono kernel: Stack: 00000300 00000000 00000000 00000000 00000000 c03bde7c c019b5d2 00000300
May  3 23:20:07 liono kernel:        cd3ce200 00000000 cd3ce348 00000002 c019dba5 d0972aa7 d09759e0 d096f000
May  3 23:20:07 liono kernel:        00000001 00000001 00000001 c011c685 d09758dc c903e000 000067d8 c91cd000
May  3 23:20:07 liono kernel: Call Trace: [revalidate_drives+82/112] revalidate_drives [kernel] 0x52
May  3 23:20:07 liono kernel: Call Trace: [<c019b5d2>] revalidate_drives [kernel] 0x52
May  3 23:20:07 liono kernel: [ide_register_module+53/64] ide_register_module [kernel] 0x35
May  3 23:20:07 liono kernel: [<c019dba5>] ide_register_module [kernel] 0x35
May  3 23:20:07 liono kernel: [aic7xxx_mod:aic7xxx_verbose+1171231/206116241] ide_cdrom_init [ide-cd] 0x187
May  3 23:20:07 liono kernel: [<d0972aa7>] ide_cdrom_init [ide-cd] 0x187
May  3 23:20:07 liono kernel: [aic7xxx_mod:aic7xxx_verbose+1183320/206104152] __insmod_ide-cd_S.data_L192 [ide-cd] 0xa0
May  3 23:20:07 liono kernel: [<d09759e0>] __insmod_ide-cd_S.data_L192 [ide-cd] 0xa0
May  3 23:20:07 liono kernel: [sys_init_module+1365/1616] sys_init_module [kernel] 0x555
May  3 23:20:07 liono kernel: [<c011c685>] sys_init_module [kernel] 0x555
May  3 23:20:07 liono kernel: [aic7xxx_mod:aic7xxx_verbose+1183060/206104412] sense_data_texts [ide-cd] 0x107c
May  3 23:20:07 liono kernel: [<d09758dc>] sense_data_texts [ide-cd] 0x107c
May  3 23:20:07 liono kernel: [aic7xxx_mod:aic7xxx_verbose+1156312/206131160] __insmod_ide-cd_O/lib/modules/2.4.9-21smp/kernel/drivers/ide/ide-cd.o_M3C472201_V132105 [ide-cd] 0x60
May  3 23:20:07 liono kernel: [<d096f060>] __insmod_ide-cd_O/lib/modules/2.4.9-21smp/kernel/drivers/ide/ide-cd.o_M3C472201_V132105 [ide-cd] 0x60
May  3 23:20:07 liono kernel: [system_call+51/56] system_call [kernel] 0x33
May  3 23:20:07 liono kernel: [<c010719b>] system_call [kernel] 0x33
May  3 23:20:07 liono kernel: [__put_unused_buffer_head+107/416] __put_unused_buffer_head [kernel] 0x6b
May  3 23:20:07 liono kernel: [<c014002b>] __put_unused_buffer_head [kernel] 0x6b
May  3 23:20:07 liono kernel:
May  3 23:20:07 liono kernel:
May  3 23:20:07 liono kernel: Code: 8b 40 28 85 c0 74 04 56 ff d0 5a 80 a6 b6 00 00 00 fb 8d 86

----

So what this tells me is that (probably) a NULL pointer was dereferenced while looking for a structure 
member with an offset of 40 (0x28) bytes. Looking through the ide_revalidate_disk function (ide.c) I find
that the only structure member being referenced, which also has an offset of 40 is drive->driver->revalidate 
(via the DRIVER macro):

    if (DRIVER(drive)->revalidate)

But there is no check for driver != NULL before it is dereferenced. In many other places throughout ide.c 
these explicit checks are present.

The attached patch (against 2.4.18) adds this explicit check.

--
Paul Clements
SteelEye Technology
[e-mail]

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