From f7e43672683b097bb074a8fe7af9bc600a23f231 Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Wed, 18 Apr 2018 11:51:56 -0700 Subject: [PATCH] llc: hold llc_sap before release_sock() syzbot reported we still access llc->sap in llc_backlog_rcv() after it is freed in llc_sap_remove_socket(): Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x1b9/0x294 lib/dump_stack.c:113 print_address_description+0x6c/0x20b mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412 __asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430 llc_conn_ac_send_sabme_cmd_p_set_x+0x3a8/0x460 net/llc/llc_c_ac.c:785 llc_exec_conn_trans_actions net/llc/llc_conn.c:475 [inline] llc_conn_service net/llc/llc_conn.c:400 [inline] llc_conn_state_process+0x4e1/0x13a0 net/llc/llc_conn.c:75 llc_backlog_rcv+0x195/0x1e0 net/llc/llc_conn.c:891 sk_backlog_rcv include/net/sock.h:909 [inline] __release_sock+0x12f/0x3a0 net/core/sock.c:2335 release_sock+0xa4/0x2b0 net/core/sock.c:2850 llc_ui_release+0xc8/0x220 net/llc/af_llc.c:204 llc->sap is refcount'ed and llc_sap_remove_socket() is paired with llc_sap_add_socket(). This can be amended by holding its refcount before llc_sap_remove_socket() and releasing it after release_sock(). Reported-by: Signed-off-by: Cong Wang Signed-off-by: David S. Miller --- net/llc/af_llc.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c index 01dcc0823d1f..6d29b2b94e84 100644 --- a/net/llc/af_llc.c +++ b/net/llc/af_llc.c @@ -189,6 +189,7 @@ static int llc_ui_release(struct socket *sock) { struct sock *sk = sock->sk; struct llc_sock *llc; + struct llc_sap *sap; if (unlikely(sk == NULL)) goto out; @@ -199,9 +200,15 @@ static int llc_ui_release(struct socket *sock) llc->laddr.lsap, llc->daddr.lsap); if (!llc_send_disc(sk)) llc_ui_wait_for_disc(sk, sk->sk_rcvtimeo); + sap = llc->sap; + /* Hold this for release_sock(), so that llc_backlog_rcv() could still + * use it. + */ + llc_sap_hold(sap); if (!sock_flag(sk, SOCK_ZAPPED)) llc_sap_remove_socket(llc->sap, sk); release_sock(sk); + llc_sap_put(sap); if (llc->dev) dev_put(llc->dev); sock_put(sk); -- 2.30.2