From: Oleksij Rempel o.rempel@pengutronix.de

syzbot reproduced following crash:

=============================================================================== kasan: CONFIG_KASAN_INLINE enabled kasan: GPF could be caused by NULL-ptr deref or user memory access general protection fault: 0000 [#1] PREEMPT SMP KASAN CPU: 0 PID: 9844 Comm: syz-executor.0 Not tainted 5.4.0-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:__lock_acquire+0x1254/0x4a00 kernel/locking/lockdep.c:3828 Code: 00 0f 85 96 24 00 00 48 81 c4 f0 00 00 00 5b 41 5c 41 5d 41 5e 41 5f 5d c3 48 b8 00 00 00 00 00 fc ff df 4c 89 f2 48 c1 ea 03 <80> 3c 02 00 0f 85 0b 28 00 00 49 81 3e 20 19 78 8a 0f 84 5f ee ff RSP: 0018:ffff888099c3fb48 EFLAGS: 00010006 RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000218 RSI: 0000000000000000 RDI: 0000000000000001 RBP: ffff888099c3fc60 R08: 0000000000000001 R09: 0000000000000001 R10: fffffbfff146e1d0 R11: ffff888098720400 R12: 00000000000010c0 R13: 0000000000000000 R14: 00000000000010c0 R15: 0000000000000000 FS: 00007f0559e98700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fe4d89e0000 CR3: 0000000099606000 CR4: 00000000001406f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4485 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline] _raw_spin_lock_bh+0x33/0x50 kernel/locking/spinlock.c:175 spin_lock_bh include/linux/spinlock.h:343 [inline] j1939_jsk_del+0x32/0x210 net/can/j1939/socket.c:89 j1939_sk_bind+0x2ea/0x8f0 net/can/j1939/socket.c:448 __sys_bind+0x239/0x290 net/socket.c:1648 __do_sys_bind net/socket.c:1659 [inline] __se_sys_bind net/socket.c:1657 [inline] __x64_sys_bind+0x73/0xb0 net/socket.c:1657 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x45a679 Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f0559e97c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000031 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a679 RDX: 0000000000000018 RSI: 0000000020000240 RDI: 0000000000000003 RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f0559e986d4 R13: 00000000004c09e9 R14: 00000000004d37d0 R15: 00000000ffffffff Modules linked in: ------------[ cut here ]------------ WARNING: CPU: 0 PID: 9844 at kernel/locking/mutex.c:1419 mutex_trylock+0x279/0x2f0 kernel/locking/mutex.c:1427 ===============================================================================

This issues was caused by null pointer deference. Where j1939_sk_bind() was using currently not existing priv.

Possible scenario may look as following: cpu0 cpu1 bind() bind() j1939_sk_bind() j1939_sk_bind() priv = jsk->priv; priv = jsk->priv; lock_sock(sock->sk); priv = j1939_netdev_start(ndev); j1939_jsk_add(priv, jsk); jsk->priv = priv; relase_sock(sock->sk); lock_sock(sock->sk); j1939_jsk_del(priv, jsk); ..... ooops ......

With this patch we move "priv = jsk->priv;" after the lock, to avoid assigning of wrong priv pointer.

Reported-by: syzbot+99e9e1b200a1e363237d@syzkaller.appspotmail.com Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol") Signed-off-by: Oleksij Rempel o.rempel@pengutronix.de Cc: linux-stable stable@vger.kernel.org # >= v5.4 Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de --- net/can/j1939/socket.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c index de09b0a65791..f7587428febd 100644 --- a/net/can/j1939/socket.c +++ b/net/can/j1939/socket.c @@ -423,9 +423,9 @@ static int j1939_sk_bind(struct socket *sock, struct sockaddr *uaddr, int len) { struct sockaddr_can *addr = (struct sockaddr_can *)uaddr; struct j1939_sock *jsk = j1939_sk(sock->sk); - struct j1939_priv *priv = jsk->priv; - struct sock *sk = sock->sk; - struct net *net = sock_net(sk); + struct j1939_priv *priv; + struct sock *sk; + struct net *net; int ret = 0;

ret = j1939_sk_sanity_check(addr, len); @@ -434,6 +434,10 @@ static int j1939_sk_bind(struct socket *sock, struct sockaddr *uaddr, int len)

lock_sock(sock->sk);

+ priv = jsk->priv; + sk = sock->sk; + net = sock_net(sk); + /* Already bound to an interface? */ if (jsk->state & J1939_SOCK_BOUND) { /* A re-bind() to a different interface is not