[PATCH 4.14 24/53] ALSA: seq: Fix race of get-subscription call vs port-delete ioctls

[Greg Kroah-Hartman]

[ Upstream commit 2eabc5ec8ab4d4748a82050dfcb994119b983750 ]

The snd_seq_ioctl_get_subscription() retrieves the port subscriber
information as a pointer, while the object isn't protected, hence it
may be deleted before the actual reference.  This race was spotted by
syzkaller and may lead to a UAF.

The fix is simply copying the data in the lookup function that
performs in the rwsem to protect against the deletion.

Reported-by: syzbot+9437020c82413d002...@syzkaller.appspotmail.com
Signed-off-by: Takashi Iwai <ti...@suse.de>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 sound/core/seq/seq_clientmgr.c | 10 ++--------
 sound/core/seq/seq_ports.c     | 13 ++++++++-----
 sound/core/seq/seq_ports.h     |  5 +++--
 3 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
index 692631bd4a35..068880ac47b5 100644
--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -1904,20 +1904,14 @@ static int snd_seq_ioctl_get_subscription(struct 
snd_seq_client *client,
        int result;
        struct snd_seq_client *sender = NULL;
        struct snd_seq_client_port *sport = NULL;
-       struct snd_seq_subscribers *p;
 
        result = -EINVAL;
        if ((sender = snd_seq_client_use_ptr(subs->sender.client)) == NULL)
                goto __end;
        if ((sport = snd_seq_port_use_ptr(sender, subs->sender.port)) == NULL)
                goto __end;
-       p = snd_seq_port_get_subscription(&sport->c_src, &subs->dest);
-       if (p) {
-               result = 0;
-               *subs = p->info;
-       } else
-               result = -ENOENT;
-
+       result = snd_seq_port_get_subscription(&sport->c_src, &subs->dest,
+                                              subs);
       __end:
        if (sport)
                snd_seq_port_unlock(sport);
diff --git a/sound/core/seq/seq_ports.c b/sound/core/seq/seq_ports.c
index d3fc73ac230b..c8fa4336bccd 100644
--- a/sound/core/seq/seq_ports.c
+++ b/sound/core/seq/seq_ports.c
@@ -635,20 +635,23 @@ int snd_seq_port_disconnect(struct snd_seq_client 
*connector,
 
 
 /* get matched subscriber */
-struct snd_seq_subscribers *snd_seq_port_get_subscription(struct 
snd_seq_port_subs_info *src_grp,
-                                                         struct snd_seq_addr 
*dest_addr)
+int snd_seq_port_get_subscription(struct snd_seq_port_subs_info *src_grp,
+                                 struct snd_seq_addr *dest_addr,
+                                 struct snd_seq_port_subscribe *subs)
 {
-       struct snd_seq_subscribers *s, *found = NULL;
+       struct snd_seq_subscribers *s;
+       int err = -ENOENT;
 
        down_read(&src_grp->list_mutex);
        list_for_each_entry(s, &src_grp->list_head, src_list) {
                if (addr_match(dest_addr, &s->info.dest)) {
-                       found = s;
+                       *subs = s->info;
+                       err = 0;
                        break;
                }
        }
        up_read(&src_grp->list_mutex);
-       return found;
+       return err;
 }
 
 /*
diff --git a/sound/core/seq/seq_ports.h b/sound/core/seq/seq_ports.h
index 26bd71f36c41..06003b36652e 100644
--- a/sound/core/seq/seq_ports.h
+++ b/sound/core/seq/seq_ports.h
@@ -135,7 +135,8 @@ int snd_seq_port_subscribe(struct snd_seq_client_port *port,
                           struct snd_seq_port_subscribe *info);
 
 /* get matched subscriber */
-struct snd_seq_subscribers *snd_seq_port_get_subscription(struct 
snd_seq_port_subs_info *src_grp,
-                                                         struct snd_seq_addr 
*dest_addr);
+int snd_seq_port_get_subscription(struct snd_seq_port_subs_info *src_grp,
+                                 struct snd_seq_addr *dest_addr,
+                                 struct snd_seq_port_subscribe *subs);
 
 #endif
-- 
2.20.1