[PATCH net] sctp: handle the error returned from sctp_auth_asoc_init_active_key

[PATCH net] sctp: handle the error returned from sctp_auth_asoc_init_active_key

[Xin Long]

When it returns an error from sctp_auth_asoc_init_active_key(), the
active_key is actually not updated. The old sh_key will be freeed
while it's still used as active key in asoc. Then an use-after-free
will be triggered when sending patckets, as found by syzbot:

  sctp_auth_shkey_hold+0x22/0xa0 net/sctp/auth.c:112
  sctp_set_owner_w net/sctp/socket.c:132 [inline]
  sctp_sendmsg_to_asoc+0xbd5/0x1a20 net/sctp/socket.c:1863
  sctp_sendmsg+0x1053/0x1d50 net/sctp/socket.c:2025
  inet_sendmsg+0x99/0xe0 net/ipv4/af_inet.c:819
  sock_sendmsg_nosec net/socket.c:714 [inline]
  sock_sendmsg+0xcf/0x120 net/socket.c:734

This patch is to fix it by not replacing the sh_key when it returns
errors from sctp_auth_asoc_init_active_key() in sctp_auth_set_key().
For sctp_auth_set_active_key(), old active_key_id will be set back
to asoc->active_key_id when the same thing happens.

Fixes: 58acd1009226 ("sctp: update active_key for asoc when old key is being replaced")
Reported-by: syzbot+a236dd8e9622ed8954a3@syzkaller.appspotmail.com
Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/sctp/auth.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/net/sctp/auth.c b/net/sctp/auth.c
index db6b7373d16c..34964145514e 100644
--- a/net/sctp/auth.c
+++ b/net/sctp/auth.c
@@ -863,12 +863,17 @@ int sctp_auth_set_key(struct sctp_endpoint *ep,
 	}
 
 	list_del_init(&shkey->key_list);
-	sctp_auth_shkey_release(shkey);
 	list_add(&cur_key->key_list, sh_keys);
 
-	if (asoc && asoc->active_key_id == auth_key->sca_keynumber)
-		sctp_auth_asoc_init_active_key(asoc, GFP_KERNEL);
+	if (asoc && asoc->active_key_id == auth_key->sca_keynumber &&
+	    sctp_auth_asoc_init_active_key(asoc, GFP_KERNEL)) {
+		list_del_init(&cur_key->key_list);
+		sctp_auth_shkey_release(cur_key);
+		list_add(&shkey->key_list, sh_keys);
+		return -ENOMEM;
+	}
 
+	sctp_auth_shkey_release(shkey);
 	return 0;
 }
 
@@ -902,8 +907,13 @@ int sctp_auth_set_active_key(struct sctp_endpoint *ep,
 		return -EINVAL;
 
 	if (asoc) {
+		__u16  active_key_id = asoc->active_key_id;
+
 		asoc->active_key_id = key_id;
-		sctp_auth_asoc_init_active_key(asoc, GFP_KERNEL);
+		if (sctp_auth_asoc_init_active_key(asoc, GFP_KERNEL)) {
+			asoc->active_key_id = active_key_id;
+			return -ENOMEM;
+		}
 	} else
 		ep->active_key_id = key_id;
 
-- 
2.31.1

Re: [PATCH net] sctp: handle the error returned from sctp_auth_asoc_init_active_key

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (master)
by David S. Miller <davem@davemloft.net>:

On Wed, 28 Sep 2022 14:10:13 -0400 you wrote:
> When it returns an error from sctp_auth_asoc_init_active_key(), the
> active_key is actually not updated. The old sh_key will be freeed
> while it's still used as active key in asoc. Then an use-after-free
> will be triggered when sending patckets, as found by syzbot:
> 
>   sctp_auth_shkey_hold+0x22/0xa0 net/sctp/auth.c:112
>   sctp_set_owner_w net/sctp/socket.c:132 [inline]
>   sctp_sendmsg_to_asoc+0xbd5/0x1a20 net/sctp/socket.c:1863
>   sctp_sendmsg+0x1053/0x1d50 net/sctp/socket.c:2025
>   inet_sendmsg+0x99/0xe0 net/ipv4/af_inet.c:819
>   sock_sendmsg_nosec net/socket.c:714 [inline]
>   sock_sendmsg+0xcf/0x120 net/socket.c:734
> 
> [...]

Here is the summary with links:
  - [net] sctp: handle the error returned from sctp_auth_asoc_init_active_key
    https://git.kernel.org/netdev/net/c/022152aaebe1

You are awesome, thank you!
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