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From: Pavel Begunkov <[email protected]>
To: Jens Axboe <[email protected]>, [email protected]
Subject: Re: [PATCH v2] io_uring: fix dead-hung for non-iter fixed rw
Date: Sun, 24 Nov 2019 20:52:03 +0300	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>


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On 24/11/2019 20:10, Jens Axboe wrote:
> On 11/24/19 1:58 AM, Pavel Begunkov wrote:
>> Read/write requests to devices without implemented read/write_iter
>> using fixed buffers causes general protection fault, which totally
>> hangs a machine.
>>
>> io_import_fixed() initialises iov_iter with bvec, but loop_rw_iter()
>> accesses it as iovec, so dereferencing random address.
>>
>> kmap() page by page in this case
> 
> This looks good to me, much cleaner/simpler. I've added a few pipe fixed
> buffer tests to liburing as well. Didn't crash for me, but obvious
> garbage coming out. I've flagged this for stable as well.
> 
The problem I have is that __user pointer is meant to be checked
for not being a kernel address. I suspect, it could fail in some
device, which double checks the pointer after vfs (e.g. using access_ok()).
Am I wrong? Not a fault at least...

#define access_ok(...) __range_not_ok(addr, user_addr_max());

BTW, is there anybody testing it for non x86-64 arch?

-- 
Pavel Begunkov


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  reply	other threads:[~2019-11-24 17:52 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <[email protected]>
2019-11-24  8:58 ` [PATCH v2] io_uring: fix dead-hung for non-iter fixed rw Pavel Begunkov
2019-11-24 17:10   ` Jens Axboe
2019-11-24 17:52     ` Pavel Begunkov [this message]
2019-11-25  0:43       ` Jackie Liu
2019-11-25  2:38         ` Jens Axboe
2019-11-25  3:33           ` Jackie Liu
2019-11-25  3:47             ` Jens Axboe
2019-11-25 10:12             ` Pavel Begunkov
2019-11-25  2:37       ` Jens Axboe
2019-11-25 10:46         ` Pavel Begunkov

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