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authorDuoming Zhou <duoming@zju.edu.cn>2022-04-15 19:14:21 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2022-04-20 10:34:22 +0300
commit43c107021d9160f6a1610bafba6dadc0323ae548 (patch)
tree78e9e6772cbb7155fca67b1661df4a10c3e97496 /net
parentda6509fba636f7f8b2e902b1e4742fdbf1bf059f (diff)
downloadlinux-43c107021d9160f6a1610bafba6dadc0323ae548.tar.xz
ax25: Fix NULL pointer dereferences in ax25 timers
commit fc6d01ff9ef03b66d4a3a23b46fc3c3d8cf92009 upstream. The previous commit 7ec02f5ac8a5 ("ax25: fix NPD bug in ax25_disconnect") move ax25_disconnect into lock_sock() in order to prevent NPD bugs. But there are race conditions that may lead to null pointer dereferences in ax25_heartbeat_expiry(), ax25_t1timer_expiry(), ax25_t2timer_expiry(), ax25_t3timer_expiry() and ax25_idletimer_expiry(), when we use ax25_kill_by_device() to detach the ax25 device. One of the race conditions that cause null pointer dereferences can be shown as below: (Thread 1) | (Thread 2) ax25_connect() | ax25_std_establish_data_link() | ax25_start_t1timer() | mod_timer(&ax25->t1timer,..) | | ax25_kill_by_device() (wait a time) | ... | s->ax25_dev = NULL; //(1) ax25_t1timer_expiry() | ax25->ax25_dev->values[..] //(2)| ... ... | We set null to ax25_cb->ax25_dev in position (1) and dereference the null pointer in position (2). The corresponding fail log is shown below: =============================================================== BUG: kernel NULL pointer dereference, address: 0000000000000050 CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.17.0-rc6-00794-g45690b7d0 RIP: 0010:ax25_t1timer_expiry+0x12/0x40 ... Call Trace: call_timer_fn+0x21/0x120 __run_timers.part.0+0x1ca/0x250 run_timer_softirq+0x2c/0x60 __do_softirq+0xef/0x2f3 irq_exit_rcu+0xb6/0x100 sysvec_apic_timer_interrupt+0xa2/0xd0 ... This patch moves ax25_disconnect() before s->ax25_dev = NULL and uses del_timer_sync() to delete timers in ax25_disconnect(). If ax25_disconnect() is called by ax25_kill_by_device() or ax25->ax25_dev is NULL, the reason in ax25_disconnect() will be equal to ENETUNREACH, it will wait all timers to stop before we set null to s->ax25_dev in ax25_kill_by_device(). Fixes: 7ec02f5ac8a5 ("ax25: fix NPD bug in ax25_disconnect") Signed-off-by: Duoming Zhou <duoming@zju.edu.cn> Signed-off-by: David S. Miller <davem@davemloft.net> [OP: backport to 5.15: adjust context] Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'net')
-rw-r--r--net/ax25/af_ax25.c4
-rw-r--r--net/ax25/ax25_subr.c20
2 files changed, 16 insertions, 8 deletions
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index df01f790a34c..3116d8d1b5cf 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -89,20 +89,20 @@ again:
sk = s->sk;
if (!sk) {
spin_unlock_bh(&ax25_list_lock);
- s->ax25_dev = NULL;
ax25_disconnect(s, ENETUNREACH);
+ s->ax25_dev = NULL;
spin_lock_bh(&ax25_list_lock);
goto again;
}
sock_hold(sk);
spin_unlock_bh(&ax25_list_lock);
lock_sock(sk);
+ ax25_disconnect(s, ENETUNREACH);
s->ax25_dev = NULL;
if (sk->sk_socket) {
dev_put(ax25_dev->dev);
ax25_dev_put(ax25_dev);
}
- ax25_disconnect(s, ENETUNREACH);
release_sock(sk);
spin_lock_bh(&ax25_list_lock);
sock_put(sk);
diff --git a/net/ax25/ax25_subr.c b/net/ax25/ax25_subr.c
index 15ab812c4fe4..3a476e4f6cd0 100644
--- a/net/ax25/ax25_subr.c
+++ b/net/ax25/ax25_subr.c
@@ -261,12 +261,20 @@ void ax25_disconnect(ax25_cb *ax25, int reason)
{
ax25_clear_queues(ax25);
- if (!ax25->sk || !sock_flag(ax25->sk, SOCK_DESTROY))
- ax25_stop_heartbeat(ax25);
- ax25_stop_t1timer(ax25);
- ax25_stop_t2timer(ax25);
- ax25_stop_t3timer(ax25);
- ax25_stop_idletimer(ax25);
+ if (reason == ENETUNREACH) {
+ del_timer_sync(&ax25->timer);
+ del_timer_sync(&ax25->t1timer);
+ del_timer_sync(&ax25->t2timer);
+ del_timer_sync(&ax25->t3timer);
+ del_timer_sync(&ax25->idletimer);
+ } else {
+ if (!ax25->sk || !sock_flag(ax25->sk, SOCK_DESTROY))
+ ax25_stop_heartbeat(ax25);
+ ax25_stop_t1timer(ax25);
+ ax25_stop_t2timer(ax25);
+ ax25_stop_t3timer(ax25);
+ ax25_stop_idletimer(ax25);
+ }
ax25->state = AX25_STATE_0;