linux-kernel - Re: [PATCH] block: tolerate tracing of NULL bio

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Message-ID: <99c7c64d-6bd4-a0f2-efc9-84c0fc598504@kernel.dk>
Date:   Fri, 8 Sep 2017 08:25:08 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Greg Thelen <gthelen@...gle.com>
Cc:     Christoph Hellwig <hch@....de>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: tolerate tracing of NULL bio

On 09/07/2017 06:36 PM, Greg Thelen wrote:
> __get_request() can call trace_block_getrq() with bio=NULL which causes
> block_get_rq::TP_fast_assign() to deref a NULL pointer and panic.
> 
> Syzkaller fuzzer panics with
> linux-next (1d53d908b79d7870d89063062584eead4cf83448):
>   kasan: GPF could be caused by NULL-ptr deref or user memory access
>   general protection fault: 0000 [#1] SMP KASAN
>   Modules linked in:
>   CPU: 0 PID: 2983 Comm: syzkaller401111 Not tainted 4.13.0-rc7-next-20170901+ #13
>   task: ffff8801cf1da000 task.stack: ffff8801ce440000
>   RIP: 0010:perf_trace_block_get_rq+0x697/0x970 include/trace/events/block.h:384
>   RSP: 0018:ffff8801ce4473f0 EFLAGS: 00010246
>   RAX: ffff8801cf1da000 RBX: 1ffff10039c88e84 RCX: 1ffffd1ffff84d27
>   RDX: dffffc0000000001 RSI: 1ffff1003b643e7a RDI: ffffe8ffffc26938
>   RBP: ffff8801ce447530 R08: 1ffff1003b643e6c R09: ffffe8ffffc26964
>   R10: 0000000000000002 R11: fffff91ffff84d2d R12: ffffe8ffffc1f890
>   R13: ffffe8ffffc26930 R14: ffffffff85cad9e0 R15: 0000000000000000
>   FS:  0000000002641880(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 000000000043e670 CR3: 00000001d1d7a000 CR4: 00000000001406f0
>   DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>   DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>   Call Trace:
>     trace_block_getrq include/trace/events/block.h:423 [inline]
>     __get_request block/blk-core.c:1283 [inline]
>     get_request+0x1518/0x23b0 block/blk-core.c:1355
>     blk_old_get_request block/blk-core.c:1402 [inline]
>     blk_get_request+0x1d8/0x3c0 block/blk-core.c:1427
>     sg_scsi_ioctl+0x117/0x750 block/scsi_ioctl.c:451
>     sg_ioctl+0x192d/0x2ed0 drivers/scsi/sg.c:1070
>     vfs_ioctl fs/ioctl.c:45 [inline]
>     do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:685
>     SYSC_ioctl fs/ioctl.c:700 [inline]
>     SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
>     entry_SYSCALL_64_fastpath+0x1f/0xbe
> 
> block_get_rq::TP_fast_assign() has multiple redundant ->dev assignments.
> Only one of them is NULL tolerant.  Favor the NULL tolerant one.

Applied, thanks.

-- 
Jens Axboe