Re: [PATCH] fix offset checks in do_sendfile to use unsigned values

[Steve French <smfrench@gmail.com>]

On Wed, Jul 22, 2009 at 9:13 AM, Jeff Layton<jlayton@redhat.com> wrote:
> On Wed, 2009-07-22 at 15:51 +0200, Johannes Weiner wrote:
>
>> > Any of these patches will fix the immediate problem, but I think this
>> > code in do_sendfile should still account for the possibility that
>> > someone can set the value larger than MAX_LFS_FILESIZE. An alternative
>> > is to consider a WARN at mount time when filesystems set s_maxbytes
>> > larger than that value (that might help catch out of tree filesystems
>> > that get this wrong and prevent this sort of silent bug in the future).
>>
>> Isn't MAX_LFS_FILESIZE by definition the maximum sensible value for
>> s_maxbytes?
>>
>
> Pretty much, but nothing seems to enforce it or let you know when you've
> exceeded it. It sort of seems like s_maxbytes ought to be loff_t or
> something instead of an unsigned long long. A negative value there
> wouldn't make much sense, but no one would be as tempted to set it
> higher than MAX_LFS_FILESIZE.
>
>> > Either way, the patch I posted for this isn't sufficient since there are
>> > some checks that need to be done against the signed values (the
>> > (pos < 0) check, for instance). I'll post a respun patch in a bit that
>> > should fix up those problems.
>>
>> That is already handled in rw_verify_area(), I think, so we should be
>> able to drop it completely.
>
> If we get rid of those checks altogether, then "max" will become unused.
> Is that really OK here?
>
> For discussion purposes, I've attached a replacement patch that I'm
> working with now.

Looks fine to me


-- 
Thanks,

Steve