Re: fs: out of bounds on stack in iov_iter_advance

[Jens Axboe <axboe@kernel.dk>]

On 11/10/2015 07:40 PM, Jens Axboe wrote:
> On 11/10/2015 07:31 PM, Linus Torvalds wrote:
>> On Tue, Nov 10, 2015 at 6:25 PM, Jens Axboe <axboe@kernel.dk> wrote:
>>> On Tue, Nov 10 2015, Linus Torvalds wrote:
>>>> Al, ping?
>>>>
>>>> On Thu, Nov 5, 2015 at 7:38 PM, Linus Torvalds
>>>> <torvalds@linux-foundation.org> wrote:
>>>>> On Thu, Nov 5, 2015 at 6:19 PM, Al Viro <viro@zeniv.linux.org.uk>
>>>>> wrote:
>>>>>>
>>>>>> How are we going to handle that one?  I can put it into mainline pull
>>>>>> request via vfs.git, with Cc: stable, but if e.g. Jens prefers to
>>>>>> take it
>>>>>> via the block tree, I'll be glad to leave it for him to deal with.
>>>>>
>>>>> Put it in the vfs tree (I'm hoping for a pull request soon..)
>>>>>
>>>>> I pulled the block trees from Jens yesterday, so there is presumably
>>>>> nothing pending there right now.
>>>>
>>>> Apparently my "hoping for a pull request soon" was ridiculously
>>>> optimistic.
>>>>
>>>> Al, looking at the most recent linux-next, most of the vfs commits
>>>> there seem to be committed in the last day or two. I'm getting the
>>>> feeling that that is all 4.5 material by now.
>>>>
>>>> Should I just take the iov patch as-is, since apparently no vfs pull
>>>> request is happening this merge cycle? And no, I'm not taking
>>>> "developed during the second week of the merge window, and sent in the
>>>> last few days of it". I'm done with that.
>>>
>>> I've got 8 other patches pending for a post core merge, just waiting for
>>> the last core pull request to go in. I haven't seen this iov iter fix,
>>> though.
>>
>> It was in this thread, looked like this (without the whitespace damage):
>>
>>      dax_io(): don't let non-error value escape via retval instead of
>> EFAULT
>>
>>      Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
>>      ---
>>      diff --git a/fs/dax.c b/fs/dax.c
>>      index a86d3cc..7b653e9 100644
>>      --- a/fs/dax.c
>>      +++ b/fs/dax.c
>>      @@ -169,8 +169,10 @@ static ssize_t dax_io(struct inode *inode,
>> struct iov_iter *iter,
>>                      else
>>                              len = iov_iter_zero(max - pos, iter);
>>
>>      -               if (!len)
>>      +               if (!len) {
>>      +                       retval = -EFAULT;
>>                              break;
>>      +               }
>>
>>                      pos += len;
>>                      addr += len;
>>
>>
>> although I don't think I saw a confirmation that that was what Sasha
>> actually hit (but Sasha had narrowed it down to DAX, so it looks
>> possible/likely)
>
> I found it right after sending that email. Patch looks pretty straight
> forward, at least from the case of max - pos != 0 and len == 0 on
> return. Might be cleaner to add a
>
> if (retval < 0)
>      break;
>
> check, that should be the case where max == pos anyway. But we'd
> potentially return -Exx into -EFAULT for that case with the patch.
>
> Hmm?

So we already do that, in the 'if' above. I think the patch looks fine.

-- 
Jens Axboe