Re: [PATCH] block: fix NULL pointer dereference in account statistics with IDE

[Jens Axboe]

On 12/10/19 11:47 AM, Logan Gunthorpe wrote:
> The IDE driver creates some passthru requests which never get
> submitted to the block layer in such a way that blk_account_io_start()
> gets called. However, the driver still calls __blk_mq_end_request() in
> ide_end_rq() which will call blk_account_io_completion() which tries
> to dereferences req->part which is never set. See ide_prep_sense() for
> an example of where these requests come from.
> 
> To fix this, blk_account_io_completion() and blk_account_io_done()
> should do nothing if req->part is not set.
> 
> The back trace of this bug is:
> 
>     BUG: kernel NULL pointer dereference, address: 000002ac
>     #PF: supervisor write access in kernel mode
>     #PF: error_code(0x0002) - not-present page
>     *pde = 00000000
>     Oops: 0002 [#1]
>     CPU: 0 PID: 237 Comm: kworker/0:1H Not tainted
>     5.4.0-rc2-00011-g48d9b0d43105e #1
>     Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1
>     04/01/2014
>     Workqueue: kblockd drive_rq_insert_work
>     EIP: blk_account_io_completion+0x7a/0xf0
>     Code: 89 54 24 08 31 d2 89 4c 24 04 31 c9 c7 04 24 02 00 00 00 c1 ee
>     09 e8 f5 21 a6 ff e8 70 5c a7 ff 8b 53 60 8d 04 bd 00 00 00 00 <01> b4
>     02 ac 02 00 00 8b 9a 88 02 00 00 85 db 74 11 85 d2 74 51 8b
>     EAX: 00000000 EBX: f5b80000 ECX: 00000000 EDX: 00000000
>     ESI: 00000000 EDI: 00000000 EBP: f3031e70 ESP: f3031e54
>     DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068 EFLAGS: 00010046
>     CR0: 80050033 CR2: 000002ac CR3: 03c25000 CR4: 000406d0
>     Call Trace:
>      <IRQ>
>       blk_update_request+0x85/0x420
>       ide_end_rq+0x38/0xa0
>       ide_complete_rq+0x3d/0x70
>       cdrom_newpc_intr+0x258/0xba0
>       ide_intr+0x135/0x250
>       __handle_irq_event_percpu+0x3e/0x250
>       handle_irq_event_percpu+0x1f/0x50
>       handle_irq_event+0x32/0x60
>       handle_level_irq+0x6c/0x110
>       handle_irq+0x72/0xa0
>       </IRQ>
>       do_IRQ+0x45/0xad
>       common_interrupt+0x115/0x11c

Why not just:

diff --git a/block/blk.h b/block/blk.h
index 6842f28c033e..d7407b5d0200 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -250,7 +250,7 @@ int blk_dev_init(void);
  */
 static inline bool blk_do_io_stat(struct request *rq)
 {
-	return rq->rq_disk && (rq->rq_flags & RQF_IO_STAT);
+	return rq->part && rq->rq_disk && (rq->rq_flags & RQF_IO_STAT);
 }
 
 static inline void req_set_nomerge(struct request_queue *q, struct request *req)

-- 
Jens Axboe