netdev - Re: [syzbot] [net?] [nfc?] KASAN: slab-use-after-free Read in nfc_alloc_send

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Date: Mon, 13 Nov 2023 17:34:21 +0530
From: Siddh Raman Pant <code@...dh.me>
To: syzbot+bbe84a4010eeea00982d@...kaller.appspotmail.com
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [net?] [nfc?] KASAN: slab-use-after-free Read in
 nfc_alloc_send_skb

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

diff --git a/net/nfc/llcp_sock.c b/net/nfc/llcp_sock.c
index 645677f84dba..bc97cd6971bd 100644
--- a/net/nfc/llcp_sock.c
+++ b/net/nfc/llcp_sock.c
@@ -795,6 +795,11 @@ static int llcp_sock_sendmsg(struct socket *sock, struct msghdr *msg,
                return -ENODEV;
        }
 
+       if (sk->sk_state != LLCP_CONNECTED) {
+               release_sock(sk);
+               return -ENOTCONN;
+       }
+
        if (sk->sk_type == SOCK_DGRAM) {
                DECLARE_SOCKADDR(struct sockaddr_nfc_llcp *, addr,
                                 msg->msg_name);
@@ -810,11 +815,6 @@ static int llcp_sock_sendmsg(struct socket *sock, struct msghdr *msg,
                                              msg, len);
        }
 
-       if (sk->sk_state != LLCP_CONNECTED) {
-               release_sock(sk);
-               return -ENOTCONN;
-       }
-
        release_sock(sk);
 
        return nfc_llcp_send_i_frame(llcp_sock, msg, len);