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ALSA: seq: Clear variable event pointer on read

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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: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Kyle Zeng <kylebot@openai.com>
Link: https://patch.msgid.link/20260607004129.61345-1-kylebot@openai.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Kyle Zeng 2026-06-06 17:41:29 -07:00 committed by Takashi Iwai
parent 98fe3988a2
commit 705dd6dcbc
1 changed files with 1 additions and 0 deletions
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1
sound/core/seq/seq_clientmgr.c
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@ -441,6 +441,7 @@ static ssize_t snd_seq_read(struct file *file, char __user *buf, size_t count,
memcpy(&tmpev, &cell->event, aligned_size);
tmpev.data.ext.len &= ~SNDRV_SEQ_EXT_MASK;
tmpev.data.ext.ptr = NULL;
if (copy_to_user(buf, &tmpev, aligned_size)) {
err = -EFAULT;
break;