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

[Jeff Layton]

 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.
-- 
Jeff Layton <jlayton@xxxxxxxxxx>