From: Fedor Pchelkin pchelkin@ispras.ru

Syzkaller reports the following failure:

BUG: KASAN: use-after-free in kref_put include/linux/kref.h:64 [inline] BUG: KASAN: use-after-free in j1939_priv_put+0x25/0xa0 net/can/j1939/main.c:172 Write of size 4 at addr ffff888141c15058 by task swapper/3/0

CPU: 3 PID: 0 Comm: swapper/3 Not tainted 5.10.144-syzkaller #0 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 Call Trace: <IRQ> __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x107/0x167 lib/dump_stack.c:118 print_address_description.constprop.0+0x1c/0x220 mm/kasan/report.c:385 __kasan_report mm/kasan/report.c:545 [inline] kasan_report.cold+0x1f/0x37 mm/kasan/report.c:562 check_memory_region_inline mm/kasan/generic.c:186 [inline] check_memory_region+0x145/0x190 mm/kasan/generic.c:192 instrument_atomic_read_write include/linux/instrumented.h:101 [inline] atomic_fetch_sub_release include/asm-generic/atomic-instrumented.h:220 [inline] __refcount_sub_and_test include/linux/refcount.h:272 [inline] __refcount_dec_and_test include/linux/refcount.h:315 [inline] refcount_dec_and_test include/linux/refcount.h:333 [inline] kref_put include/linux/kref.h:64 [inline] j1939_priv_put+0x25/0xa0 net/can/j1939/main.c:172 j1939_sk_sock_destruct+0x44/0x90 net/can/j1939/socket.c:374 __sk_destruct+0x4e/0x820 net/core/sock.c:1784 rcu_do_batch kernel/rcu/tree.c:2485 [inline] rcu_core+0xb35/0x1a30 kernel/rcu/tree.c:2726 __do_softirq+0x289/0x9a3 kernel/softirq.c:298 asm_call_irq_on_stack+0x12/0x20 </IRQ> __run_on_irqstack arch/x86/include/asm/irq_stack.h:26 [inline] run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:77 [inline] do_softirq_own_stack+0xaa/0xe0 arch/x86/kernel/irq_64.c:77 invoke_softirq kernel/softirq.c:393 [inline] __irq_exit_rcu kernel/softirq.c:423 [inline] irq_exit_rcu+0x136/0x200 kernel/softirq.c:435 sysvec_apic_timer_interrupt+0x4d/0x100 arch/x86/kernel/apic/apic.c:1095 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:635

Allocated by task 1141: kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48 kasan_set_track mm/kasan/common.c:56 [inline] __kasan_kmalloc.constprop.0+0xc9/0xd0 mm/kasan/common.c:461 kmalloc include/linux/slab.h:552 [inline] kzalloc include/linux/slab.h:664 [inline] j1939_priv_create net/can/j1939/main.c:131 [inline] j1939_netdev_start+0x111/0x860 net/can/j1939/main.c:268 j1939_sk_bind+0x8ea/0xd30 net/can/j1939/socket.c:485 __sys_bind+0x1f2/0x260 net/socket.c:1645 __do_sys_bind net/socket.c:1656 [inline] __se_sys_bind net/socket.c:1654 [inline] __x64_sys_bind+0x6f/0xb0 net/socket.c:1654 do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xc6

Freed by task 1141: kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48 kasan_set_track+0x1c/0x30 mm/kasan/common.c:56 kasan_set_free_info+0x1b/0x30 mm/kasan/generic.c:355 __kasan_slab_free+0x112/0x170 mm/kasan/common.c:422 slab_free_hook mm/slub.c:1542 [inline] slab_free_freelist_hook+0xad/0x190 mm/slub.c:1576 slab_free mm/slub.c:3149 [inline] kfree+0xd9/0x3b0 mm/slub.c:4125 j1939_netdev_start+0x5ee/0x860 net/can/j1939/main.c:300 j1939_sk_bind+0x8ea/0xd30 net/can/j1939/socket.c:485 __sys_bind+0x1f2/0x260 net/socket.c:1645 __do_sys_bind net/socket.c:1656 [inline] __se_sys_bind net/socket.c:1654 [inline] __x64_sys_bind+0x6f/0xb0 net/socket.c:1654 do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xc6

It can be caused by this scenario:

CPU0 CPU1 j1939_sk_bind(socket0, ndev0, ...) j1939_netdev_start() j1939_sk_bind(socket1, ndev0, ...) j1939_netdev_start() mutex_lock(&j1939_netdev_lock) j1939_priv_set(ndev0, priv) mutex_unlock(&j1939_netdev_lock) if (priv_new) kref_get(&priv_new->rx_kref) return priv_new; /* inside j1939_sk_bind() */ jsk->priv = priv j1939_can_rx_register(priv) // fails j1939_priv_set(ndev, NULL) kfree(priv) j1939_sk_sock_destruct() j1939_priv_put() // <- uaf

To avoid this, call j1939_can_rx_register() under j1939_netdev_lock so that a concurrent thread cannot process j1939_priv before j1939_can_rx_register() returns.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol") Signed-off-by: Fedor Pchelkin pchelkin@ispras.ru Tested-by: Oleksij Rempel o.rempel@pengutronix.de Acked-by: Oleksij Rempel o.rempel@pengutronix.de Link: https://lore.kernel.org/r/20230526171910.227615-3-pchelkin@ispras.ru Cc: stable@vger.kernel.org Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de --- net/can/j1939/main.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/can/j1939/main.c b/net/can/j1939/main.c index 6ed79afe19a5..ecff1c947d68 100644 --- a/net/can/j1939/main.c +++ b/net/can/j1939/main.c @@ -290,16 +290,18 @@ struct j1939_priv *j1939_netdev_start(struct net_device *ndev) return priv_new; } j1939_priv_set(ndev, priv); - mutex_unlock(&j1939_netdev_lock);

ret = j1939_can_rx_register(priv); if (ret < 0) goto out_priv_put;

+ mutex_unlock(&j1939_netdev_lock); return priv;

out_priv_put: j1939_priv_set(ndev, NULL); + mutex_unlock(&j1939_netdev_lock); + dev_put(ndev); kfree(priv);