Re: [PATCH 2/2] xfs: fix various problems in xfs_atomic_write_cow_iomap_begin

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Nov 05, 2025 at 12:21:15PM +0000, John Garry wrote:
> On 04/11/2025 17:18, Darrick J. Wong wrote:
> > > Can you point out that code? I wonder if we should be rejecting anything
> > > which goes over s_maxbytes for RWF_ATOMIC.
> > generic_write_check_limits:
> > https://urldefense.com/v3/__https://elixir.bootlin.com/linux/v6.17.7/
> > source/fs/read_write.c*L1709__;Iw!!ACWV5N9M2RV99hQ!M- J1QmUWrGHUBb6gf9LHN33HxhBfk3rHcNR5z_glUHClffIPQ5UFQ1zmHpsetFGz3_3lHzUrwyAASD_90A$
> > 
> > xfs_file_dio_write_atomic -> xfs_file_write_checks ->
> > generic_write_checks -> generic_write_checks_count ->
> > generic_write_check_limits
> 
> ok, thanks for the pointer.
> 
> So should we stop any possible truncation for RWF_ATOMIC, like:
> 
> +++ b/fs/xfs/xfs_file.c
> @@ -440,6 +440,9 @@ xfs_file_write_checks(
>        if (error <= 0)
>                return error;
> 
> +       if (error != count && iocb->ki_flags & IOCB_ATOMIC)
> +               return -EINVAL;
> +
>        if (iocb->ki_flags & IOCB_NOWAIT) {
>                error = break_layout(inode, false);
>                if (error == -EWOULDBLOCK)
> 
> 
> Note that I do realize that this may be better in generic fs code.

Yeah, I think that'd be better placed in generic_write_checks_count if
_limit() changes &count.

--D

> Thanks,
> John
>