netdev - [PATCH net 1/2] net/af_iucv: fix null pointer dereference on shutdown

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Message-Id: <20201106125008.36478-2-jwi@linux.ibm.com>
Date:   Fri,  6 Nov 2020 13:50:07 +0100
From:   Julian Wiedmann <jwi@...ux.ibm.com>
To:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     linux-netdev <netdev@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Karsten Graul <kgraul@...ux.ibm.com>,
        Julian Wiedmann <jwi@...ux.ibm.com>,
        Ursula Braun <ubraun@...ux.ibm.com>
Subject: [PATCH net 1/2] net/af_iucv: fix null pointer dereference on shutdown

From: Ursula Braun <ubraun@...ux.ibm.com>

syzbot reported the following KASAN finding:

BUG: KASAN: nullptr-dereference in iucv_send_ctrl+0x390/0x3f0 net/iucv/af_iucv.c:385
Read of size 2 at addr 000000000000021e by task syz-executor907/519

CPU: 0 PID: 519 Comm: syz-executor907 Not tainted 5.9.0-syzkaller-07043-gbcf9877ad213 #0
Hardware name: IBM 3906 M04 701 (KVM/Linux)
Call Trace:
 [<00000000c576af60>] unwind_start arch/s390/include/asm/unwind.h:65 [inline]
 [<00000000c576af60>] show_stack+0x180/0x228 arch/s390/kernel/dumpstack.c:135
 [<00000000c9dcd1f8>] __dump_stack lib/dump_stack.c:77 [inline]
 [<00000000c9dcd1f8>] dump_stack+0x268/0x2f0 lib/dump_stack.c:118
 [<00000000c5fed016>] print_address_description.constprop.0+0x5e/0x218 mm/kasan/report.c:383
 [<00000000c5fec82a>] __kasan_report mm/kasan/report.c:517 [inline]
 [<00000000c5fec82a>] kasan_report+0x11a/0x168 mm/kasan/report.c:534
 [<00000000c98b5b60>] iucv_send_ctrl+0x390/0x3f0 net/iucv/af_iucv.c:385
 [<00000000c98b6262>] iucv_sock_shutdown+0x44a/0x4c0 net/iucv/af_iucv.c:1457
 [<00000000c89d3a54>] __sys_shutdown+0x12c/0x1c8 net/socket.c:2204
 [<00000000c89d3b70>] __do_sys_shutdown net/socket.c:2212 [inline]
 [<00000000c89d3b70>] __s390x_sys_shutdown+0x38/0x48 net/socket.c:2210
 [<00000000c9e36eac>] system_call+0xe0/0x28c arch/s390/kernel/entry.S:415

There is nothing to shutdown if a connection has never been established.
Besides that iucv->hs_dev is not yet initialized if a socket is in
IUCV_OPEN state and iucv->path is not yet initialized if socket is in
IUCV_BOUND state.
So, just skip the shutdown calls for a socket in these states.

Fixes: eac3731bd04c ("s390: Add AF_IUCV socket support")
Fixes: 82492a355fac ("af_iucv: add shutdown for HS transport")
Reviewed-by: Vasily Gorbik <gor@...ux.ibm.com>
Signed-off-by: Ursula Braun <ubraun@...ux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@...ux.ibm.com>
---
 net/iucv/af_iucv.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c
index d80572074667..047238f01ba6 100644
--- a/net/iucv/af_iucv.c
+++ b/net/iucv/af_iucv.c
@@ -1434,7 +1434,8 @@ static int iucv_sock_shutdown(struct socket *sock, int how)
 		break;
 	}
 
-	if (how == SEND_SHUTDOWN || how == SHUTDOWN_MASK) {
+	if ((how == SEND_SHUTDOWN || how == SHUTDOWN_MASK) &&
+	    sk->sk_state == IUCV_CONNECTED) {
 		if (iucv->transport == AF_IUCV_TRANS_IUCV) {
 			txmsg.class = 0;
 			txmsg.tag = 0;
-- 
2.17.1