Re: [PATCH] ALSA: seq: Clear variable event pointer on read

[Takashi Iwai <tiwai@suse.de>]

On Sun, 07 Jun 2026 02:41:29 +0200,
Kyle Zeng wrote:
> 
> snd_seq_read() copies a queued variable-length event header to userspace
> before expanding the payload. Queued variable-length events use
> SNDRV_SEQ_EXT_CHAINED internally, and data.ext.ptr points at the first
> extension cell.
> 
> The read side strips SNDRV_SEQ_EXT_* bits from data.ext.len before the
> copy, but it leaves data.ext.ptr untouched. A userspace sequencer client
> can therefore write a direct variable event to itself and read back the
> extension-cell kernel address from the returned header.
> 
> Clear the temporary header pointer before copy_to_user(). The original
> queued event remains unchanged and is still passed to
> snd_seq_expand_var_event(), so payload expansion keeps using the
> internal chain.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Kyle Zeng <kylebot@openai.com>

Applied to for-next branch now.  Thanks.


Takashi