Re: [dpdk-dev] [PATCH] examples/vhost_blk: fix the TOCTOU

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 11/27/19 3:36 AM, Yu, Jin wrote:
>> -----Original Message-----
>> From: Bruce Richardson <bruce.richardson@intel.com>
>> Sent: Tuesday, November 26, 2019 6:26 PM
>> To: Yu, Jin <jin.yu@intel.com>
>> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>; Bie, Tiwei
>> <tiwei.bie@intel.com>; Wang, Zhihong <zhihong.wang@intel.com>;
>> dev@dpdk.org; stable@dpdk.org
>> Subject: Re: [dpdk-dev] [PATCH] examples/vhost_blk: fix the TOCTOU
>>
>> On Tue, Nov 26, 2019 at 11:32:14PM +0800, Jin Yu wrote:
>>> Fix the time of check time of use warning in example code
>>>
>>> Coverity issue: 350589 158663
>>> Fixes: c19beb3f38cd ("examples/vhost_blk: introduce vhost storage
>>> sample")
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: Jin Yu <jin.yu@intel.com>
>>> ---
>>>  examples/vhost_blk/vhost_blk.c | 9 ++-------
>>>  1 file changed, 2 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/examples/vhost_blk/vhost_blk.c
>>> b/examples/vhost_blk/vhost_blk.c index 3182a488b..bcb4ebb0b 100644
>>> --- a/examples/vhost_blk/vhost_blk.c
>>> +++ b/examples/vhost_blk/vhost_blk.c
>>> @@ -993,11 +993,7 @@ vhost_blk_ctrlr_construct(const char *ctrlr_name)
>>>  	}
>>>  	snprintf(dev_pathname, sizeof(dev_pathname), "%s/%s", path,
>>> ctrlr_name);
>>>
>>> -	if (access(dev_pathname, F_OK) != -1) {
>>> -		if (unlink(dev_pathname) != 0)
>>> -			rte_exit(EXIT_FAILURE, "Cannot remove %s.\n",
>>> -				 dev_pathname);
>>> -	}
>>> +	unlink(dev_pathname);
>>>
>>
>> The original code did an exit if the delete failed, do you intend there to be a
>> behaviour change here? You can probably get the same behaviour if you
>> check the errno on an unlink failure, e.g. ENOENT means file doesn't exist.
>>
>> If not having the app exit on unlink failure is reasonable behaviour then
>> ignore this comment.
> 
> I considered it. I think it's ok to ignore the errno of unlink failure. This code just want
> to remove the file. There are two situations. The first one is that file doesn't exist the unlink
> fails and it's ok to ignore. The second one is that unlink fails to remove file but the next bind() 
> would fail too so I think it's ok to ignore too.

That's fine by me, but please could you mention it in the commit
message?

>> Regards,
>> /Bruce
>