Re: [PATCH] filemap: Fix bounds checking in filemap_read()

[Dave Chinner <david@fromorbit.com>]

On Fri, Sep 13, 2024 at 07:21:54PM +0100, Matthew Wilcox wrote:
> On Fri, Sep 13, 2024 at 01:57:04PM -0400, trondmy@kernel.org wrote:
> > If the caller supplies an iocb->ki_pos value that is close to the
> > filesystem upper limit, and an iterator with a count that causes us to
> > overflow that limit, then filemap_read() enters an infinite loop.
> 
> Are we guaranteed that ki_pos lies in the range [0..s_maxbytes)?
> I'm not too familiar with the upper paths of the VFS and what guarantees
> we can depend on.  If we are guaranteed that, could somebody document
> it (and indeed create kernel-doc for struct kiocb)?

filemap_read() checks this itself before doing anything else:

	if (unlikely(iocb->ki_pos >= inode->i_sb->s_maxbytes))
                return 0;

i.e. there is no guarantee provided by the upper layers, it's first
checked right here in any buffered read path...

-Dave.

-- 
Dave Chinner
david@fromorbit.com