Re: [PATCH] sysfs: prevent writing excessively large files

[Greg KH]

On Tue, Sep 15, 2026 at 08:20:17PM +0800, Edward Adam Davis wrote:
> Since atomic_write_len is not configured for sysfs_file_kfops_rw, a large
> file write via sysfs_kf_write() may result in an out-of-bounds read when
> checking for the null terminator of a string element in the kobject_actions
> array within kobject_action_type(), potentially hitting:

What sysfs file are you hitting this on?

> 
> BUG: KASAN: global-out-of-bounds in kobject_action_type lib/kobject_uevent.c:86 [inline]
> BUG: KASAN: global-out-of-bounds in kobject_synth_uevent+0x79d/0x7d0 lib/kobject_uevent.c:200
> Read of size 1 at addr ffffffff8d72559f by task syz.0.17/5917
> Call Trace:
>  kobject_action_type lib/kobject_uevent.c:86 [inline]
>  kobject_synth_uevent+0x79d/0x7d0 lib/kobject_uevent.c:200
>  bus_uevent_store+0x3d/0x90 drivers/base/bus.c:917
>  bus_attr_store+0x74/0xb0 drivers/base/bus.c:172
>  sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
>  kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
>  new_sync_write fs/read_write.c:595 [inline]
>  vfs_write+0x6af/0x1050 fs/read_write.c:687
> 
> Add atomic_write_len for sysfs_file_kfops_rw and sysfs_file_kfops_wo
> properly.
> 
> Fixes: f6acf8bb6a40 ("sysfs, kernfs: introduce kernfs_ops")

What changed to suddenly cause this to show up now if this has been
present for decades?

thanks,

greg k-h