[PATCH] ALSA: pcm: oss: Fix setup list UAF on proc write error

[PATCH] ALSA: pcm: oss: Fix setup list UAF on proc write error

[Cássio Gabriel]

snd_pcm_oss_proc_write() links a newly allocated setup entry into the
OSS setup list before duplicating the task name. If the task-name
allocation fails, the error path frees the already linked entry and
leaves setup_list pointing at freed memory.

A later OSS device open can then walk the stale list entry in
snd_pcm_oss_look_for_setup() and dereference freed memory.

Allocate the task name and initialize the setup entry before publishing
the entry on setup_list. Also fetch the initial proc read iterator only
after taking setup_mutex, so all setup_list traversal follows the same
list lifetime rules.

Reported-by: syzbot+8e498074a794999eb41c@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/6a1062b7.170a0220.35b2b7.0003.GAE@google.com
Closes: https://syzkaller.appspot.com/bug?extid=8e498074a794999eb41c
Fixes: 060d77b9c04a ("[ALSA] Fix / clean up PCM-OSS setup hooks")
Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
---
 sound/core/oss/pcm_oss.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index 33fd34f0d615..746eaf93e1a5 100644
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -2974,8 +2974,10 @@ static void snd_pcm_oss_proc_read(struct snd_info_entry *entry,
 				  struct snd_info_buffer *buffer)
 {
 	struct snd_pcm_str *pstr = entry->private_data;
-	struct snd_pcm_oss_setup *setup = pstr->oss.setup_list;
+	struct snd_pcm_oss_setup *setup;
+
 	guard(mutex)(&pstr->oss.setup_mutex);
+	setup = pstr->oss.setup_list;
 	while (setup) {
 		snd_iprintf(buffer, "%s %u %u%s%s%s%s%s%s\n",
 			    setup->task_name,
@@ -3060,6 +3062,13 @@ static void snd_pcm_oss_proc_write(struct snd_info_entry *entry,
 				buffer->error = -ENOMEM;
 				return;
 			}
+			template.task_name = kstrdup(task_name, GFP_KERNEL);
+			if (!template.task_name) {
+				kfree(setup);
+				buffer->error = -ENOMEM;
+				return;
+			}
+			*setup = template;
 			if (pstr->oss.setup_list == NULL)
 				pstr->oss.setup_list = setup;
 			else {
@@ -3067,12 +3076,7 @@ static void snd_pcm_oss_proc_write(struct snd_info_entry *entry,
 				     setup1->next; setup1 = setup1->next);
 				setup1->next = setup;
 			}
-			template.task_name = kstrdup(task_name, GFP_KERNEL);
-			if (! template.task_name) {
-				kfree(setup);
-				buffer->error = -ENOMEM;
-				return;
-			}
+			continue;
 		}
 		*setup = template;
 	}

---
base-commit: ef807cc07dec16edc7863d437e9250e20cb73741
change-id: 20260522-alsa-pcm-oss-setup-uaf-04ad4312f714

Best regards,
--  
Cássio Gabriel <cassiogabrielcontato@gmail.com>

Re: [PATCH] ALSA: pcm: oss: Fix setup list UAF on proc write error

[Takashi Iwai]

On Sat, 23 May 2026 03:09:40 +0200,
Cássio Gabriel wrote:
> 
> snd_pcm_oss_proc_write() links a newly allocated setup entry into the
> OSS setup list before duplicating the task name. If the task-name
> allocation fails, the error path frees the already linked entry and
> leaves setup_list pointing at freed memory.
> 
> A later OSS device open can then walk the stale list entry in
> snd_pcm_oss_look_for_setup() and dereference freed memory.
> 
> Allocate the task name and initialize the setup entry before publishing
> the entry on setup_list. Also fetch the initial proc read iterator only
> after taking setup_mutex, so all setup_list traversal follows the same
> list lifetime rules.
> 
> Reported-by: syzbot+8e498074a794999eb41c@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/6a1062b7.170a0220.35b2b7.0003.GAE@google.com
> Closes: https://syzkaller.appspot.com/bug?extid=8e498074a794999eb41c
> Fixes: 060d77b9c04a ("[ALSA] Fix / clean up PCM-OSS setup hooks")
> Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>

Applied now.  Thanks.


Takashi