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Subject: Re: [PATCH v2 1/3] fs/fuse, splice_write: Don't access pipe->buffers
 without pipe_lock()
To:     Vlastimil Babka <vbabka@suse.cz>,
        Miklos Szeredi <miklos@szeredi.hu>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
References: <CAJfpegvAAQTAjxLcQLefvFOQDJ6ug_G8Jggt=UZci+YnNP741A@mail.gmail.com>
 <20180717160035.9422-1-aryabinin@virtuozzo.com>
 <b7aceb99-9631-cbcf-fdec-3abef72c949d@suse.cz>
From:   Andrey Ryabinin <aryabinin@virtuozzo.com>
Message-ID: <3fcf7f4f-a9c0-f9c8-f526-ab12e283cd43@virtuozzo.com>
Date:   Thu, 13 Jun 2019 12:10:19 +0300
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On 6/12/19 11:57 AM, Vlastimil Babka wrote:
> On 7/17/18 6:00 PM, Andrey Ryabinin wrote:
>> fuse_dev_splice_write() reads pipe->buffers to determine the size of
>> 'bufs' array before taking the pipe_lock(). This is not safe as
>> another thread might change the 'pipe->buffers' between the allocation
>> and taking the pipe_lock(). So we end up with too small 'bufs' array.
>>
>> Move the bufs allocations inside pipe_lock()/pipe_unlock() to fix this.
>>
>> Fixes: dd3bb14f44a6 ("fuse: support splice() writing to fuse device")
>> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
>> Cc: <stable@vger.kernel.org>
> 
> BTW, why don't we need to do the same in fuse_dev_splice_read()?
> 

do_splice() already takes the pipe_lock() before calling ->splice_read()

> Thanks,
> Vlastimil
> 
>> ---
>>  fs/fuse/dev.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
>> index c6b88fa85e2e..702592cce546 100644
>> --- a/fs/fuse/dev.c
>> +++ b/fs/fuse/dev.c
>> @@ -1944,12 +1944,15 @@ static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
>>  	if (!fud)
>>  		return -EPERM;
>>  
>> +	pipe_lock(pipe);
>> +
>>  	bufs = kmalloc_array(pipe->buffers, sizeof(struct pipe_buffer),
>>  			     GFP_KERNEL);
>> -	if (!bufs)
>> +	if (!bufs) {
>> +		pipe_unlock(pipe);
>>  		return -ENOMEM;
>> +	}
>>  
>> -	pipe_lock(pipe);
>>  	nbuf = 0;
>>  	rem = 0;
>>  	for (idx = 0; idx < pipe->nrbufs && rem < len; idx++)
>>
>