Re: [PATCH] sysfs: upgrade OOB write by buggy .show hook into WARNing

[Alexey Dobriyan <adobriyan@gmail.com>]

On Thu, May 07, 2026 at 11:05:16AM +0200, Greg Kroah-Hartman wrote:
> On Thu, May 07, 2026 at 12:01:43PM +0300, Alexey Dobriyan wrote:

> > --- a/fs/sysfs/file.c
> > +++ b/fs/sysfs/file.c
> > @@ -70,9 +70,8 @@ static int sysfs_kf_seq_show(struct seq_file *sf, void *v)
> >  	 * The code works fine with PAGE_SIZE return but it's likely to
> >  	 * indicate truncated result or overflow in normal use cases.
> >  	 */
> > -	if (count >= (ssize_t)PAGE_SIZE) {
> > -		printk("fill_read_buffer: %pS returned bad count\n",
> > -				ops->show);
> > +	if (count >= PAGE_SIZE) {
> > +		WARN(1, "OOB write or bad count %zd at %pS\n", count, ops->show);
> 
> This is going to be interesting to see what triggers, so I'll go queue
> this up soon.
> 
> And this implies you did hit this on ext4?

The check was triggered by out-of-tree module.
ext4 is me testing the patch with a custom written buggy hook.

	/sys/alexey