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

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>
Link: https://patch.msgid.link/20260522-alsa-pcm-oss-setup-uaf-v1-1-40bdcc4d17e8@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index 33fd34f0d615d9a27897b718820bbf105876b9e1..746eaf93e1a57fb6d16a53c24c12510f71f70640 100644 (file)
--- 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;
        }