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Subject: [PATCH] net: phonet: fix BUG_ON() in pn_socket_autobind()
Author: kartikey406@gmail.com

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

pn_socket_autobind() calls pn_socket_bind() and treats
-EINVAL as a signal that the socket was already bound,
then uses BUG_ON() to verify it:

    if (err != -EINVAL)
        return err;
    BUG_ON(!pn_port(pn_sk(sock->sk)->sobject));

However, pn_socket_bind() returns -EINVAL in multiple
cases:

  1. address length too short
  2. socket not in TCP_CLOSE state
  3. socket already bound  <- only intended case

When -EINVAL comes from cases 1 or 2, sobject is still
zero (never assigned), causing BUG_ON to fire and crash
the kernel.

Fix this by checking the bound state directly via
pn_port(sobject) BEFORE calling pn_socket_bind(),
eliminating the ambiguous -EINVAL interpretation
entirely.

Reported-by: syzbot+706f5eb79044e686c794@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=706f5eb79044e686c794
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 net/phonet/socket.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/phonet/socket.c b/net/phonet/socket.c
index c4af26357144..5a55e7d14e85 100644
--- a/net/phonet/socket.c
+++ b/net/phonet/socket.c
@@ -204,14 +204,14 @@ static int pn_socket_autobind(struct socket *sock)
 	struct sockaddr_pn sa;
 	int err;
 
+	if (pn_port(pn_sk(sock->sk)->sobject))
+		return 0; /* socket was already bound */
+
 	memset(&sa, 0, sizeof(sa));
 	sa.spn_family = AF_PHONET;
 	err = pn_socket_bind(sock, (struct sockaddr_unsized *)&sa,
 			     sizeof(struct sockaddr_pn));
-	if (err != -EINVAL)
-		return err;
-	BUG_ON(!pn_port(pn_sk(sock->sk)->sobject));
-	return 0; /* socket was already bound */
+	return err;
 }
 
 static int pn_socket_connect(struct socket *sock, struct sockaddr_unsized *addr,
-- 
2.43.0