[PATCH 4.4 40/50] llc: hold llc_sap before release_sock()

From: Greg Kroah-Hartman
Date: Fri Apr 27 2018 - 10:02:07 EST

4.4-stable review patch. If anyone has any objections, please let me know.


From: Cong Wang <xiyou.wangcong@xxxxxxxxx>

[ Upstream commit f7e43672683b097bb074a8fe7af9bc600a23f231 ]

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: <syzbot+6e181fc95081c2cf9051@xxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/llc/af_llc.c | 7 +++++++
1 file changed, 7 insertions(+)

--- a/net/llc/af_llc.c
+++ b/net/llc/af_llc.c
@@ -187,6 +187,7 @@ static int llc_ui_release(struct socket
struct sock *sk = sock->sk;
struct llc_sock *llc;
+ struct llc_sap *sap;

if (unlikely(sk == NULL))
goto out;
@@ -197,9 +198,15 @@ static int llc_ui_release(struct socket
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);
+ llc_sap_put(sap);
if (llc->dev)