Re: [PATCH] sysfs: clamp show() return value in sysfs_kf_read()

[Danilo Krummrich]

On Wed May 20, 2026 at 3:07 PM CEST, Greg Kroah-Hartman wrote:
> sysfs_kf_seq_show() defends against buggy show() callbacks that return
> larger than PAGE_SIZE by clamping the value and printing a warning.
> sysfs_kf_read(), the prealloc variant, has no such defense.
>
> The only current in-tree user of __ATTR_PREALLOC is drivers/md/md.c,
> whose show() callbacks are well-behaved, so this is hardening against
> future drivers doing foolish things and out-of-tree code doing even more
> foolish things.
>
> Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
> Cc: NeilBrown <neil@xxxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Fixes: 2b75869bba67 ("sysfs/kernfs: allow attributes to request write buffer be pre-allocated.")
> Assisted-by: gregkh_clanker_t1000
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

Reviewed-by: Danilo Krummrich <dakr@xxxxxxxxxx>