Re: [PATCH] xsysace: Fix error handling in ace_setup

[Michal Simek]

On 19. 02. 19 17:49, Guenter Roeck wrote:
> If xace hardware reports a bad version number, the error handling code
> in ace_setup() calls put_disk(), followed by queue cleanup. However, since
> the disk data structure has the queue pointer set, put_disk() also
> cleans and releases the queue. This results in blk_cleanup_queue()
> accessing an already released data structure, which in turn may result
> in a crash such as the following.
> 
> [   10.681671] BUG: Kernel NULL pointer dereference at 0x00000040
> [   10.681826] Faulting instruction address: 0xc0431480
> [   10.682072] Oops: Kernel access of bad area, sig: 11 [#1]
> [   10.682251] BE PAGE_SIZE=4K PREEMPT Xilinx Virtex440
> [   10.682387] Modules linked in:
> [   10.682528] CPU: 0 PID: 1 Comm: swapper Tainted: G        W         5.0.0-rc6-next-20190218+ #2
> [   10.682733] NIP:  c0431480 LR: c043147c CTR: c0422ad8
> [   10.682863] REGS: cf82fbe0 TRAP: 0300   Tainted: G        W          (5.0.0-rc6-next-20190218+)
> [   10.683065] MSR:  00029000 <CE,EE,ME>  CR: 22000222  XER: 00000000
> [   10.683236] DEAR: 00000040 ESR: 00000000
> [   10.683236] GPR00: c043147c cf82fc90 cf82ccc0 00000000 00000000 00000000 00000002 00000000
> [   10.683236] GPR08: 00000000 00000000 c04310bc 00000000 22000222 00000000 c0002c54 00000000
> [   10.683236] GPR16: 00000000 00000001 c09aa39c c09021b0 c09021dc 00000007 c0a68c08 00000000
> [   10.683236] GPR24: 00000001 ced6d400 ced6dcf0 c0815d9c 00000000 00000000 00000000 cedf0800
> [   10.684331] NIP [c0431480] blk_mq_run_hw_queue+0x28/0x114
> [   10.684473] LR [c043147c] blk_mq_run_hw_queue+0x24/0x114
> [   10.684602] Call Trace:
> [   10.684671] [cf82fc90] [c043147c] blk_mq_run_hw_queue+0x24/0x114 (unreliable)
> [   10.684854] [cf82fcc0] [c04315bc] blk_mq_run_hw_queues+0x50/0x7c
> [   10.685002] [cf82fce0] [c0422b24] blk_set_queue_dying+0x30/0x68
> [   10.685154] [cf82fcf0] [c0423ec0] blk_cleanup_queue+0x34/0x14c
> [   10.685306] [cf82fd10] [c054d73c] ace_probe+0x3dc/0x508
> [   10.685445] [cf82fd50] [c052d740] platform_drv_probe+0x4c/0xb8
> [   10.685592] [cf82fd70] [c052abb0] really_probe+0x20c/0x32c
> [   10.685728] [cf82fda0] [c052ae58] driver_probe_device+0x68/0x464
> [   10.685877] [cf82fdc0] [c052b500] device_driver_attach+0xb4/0xe4
> [   10.686024] [cf82fde0] [c052b5dc] __driver_attach+0xac/0xfc
> [   10.686161] [cf82fe00] [c0528428] bus_for_each_dev+0x80/0xc0
> [   10.686314] [cf82fe30] [c0529b3c] bus_add_driver+0x144/0x234
> [   10.686457] [cf82fe50] [c052c46c] driver_register+0x88/0x15c
> [   10.686610] [cf82fe60] [c09de288] ace_init+0x4c/0xac
> [   10.686742] [cf82fe80] [c0002730] do_one_initcall+0xac/0x330
> [   10.686888] [cf82fee0] [c09aafd0] kernel_init_freeable+0x34c/0x478
> [   10.687043] [cf82ff30] [c0002c6c] kernel_init+0x18/0x114
> [   10.687188] [cf82ff40] [c000f2f0] ret_from_kernel_thread+0x14/0x1c
> [   10.687349] Instruction dump:
> [   10.687435] 3863ffd4 4bfffd70 9421ffd0 7c0802a6 93c10028 7c9e2378 93e1002c 38810008
> [   10.687637] 7c7f1b78 90010034 4bfffc25 813f008c <81290040> 75290100 4182002c 80810008
> [   10.688056] ---[ end trace 13c9ff51d41b9d40 ]---
> 
> Fix the problem by setting the disk queue pointer to NULL before calling
> put_disk(). A more comprehensive fix might be to rearrange the code
> to check the hardware version before initializing data structures,
> but I don't know if this would have undesirable side effects, and
> it would increase the complexity of backporting the fix to older kernels.
> 
> Fixes: 74489a91dd43a ("Add support for Xilinx SystemACE CompactFlash interface")
> Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> ---
>  drivers/block/xsysace.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/block/xsysace.c b/drivers/block/xsysace.c
> index 87ccef4bd69e..32a21b8d1d85 100644
> --- a/drivers/block/xsysace.c
> +++ b/drivers/block/xsysace.c
> @@ -1090,6 +1090,8 @@ static int ace_setup(struct ace_device *ace)
>  	return 0;
>  
>  err_read:
> +	/* prevent double queue cleanup */
> +	ace->gd->queue = NULL;
>  	put_disk(ace->gd);
>  err_alloc_disk:
>  	blk_cleanup_queue(ace->queue);
> 

This driver is quite old and we are not actively using/testing it.
Are you wiring that up with qemu?

Maybe it should be labeled differently in MAINTAINERS file.

Anyway whatever fix is fine for me.

Acked-by: Michal Simek <michal.simek@xxxxxxxxxx>

Thanks,
Michal