Vulnerability: There are use-after-free vulnerabilities caused by timer handler in net/rose/rose_timer.c of linux that allow attackers to crash linux kernel without any privileges.
Vulnerability ID: CVE-2022-2318
CWE: CWE-416
Severity score: 6.9
Project: https://github.com/torvalds/linux
Published: 2022-07-06
File: net/rose/rose_timer.c
Commit message: net: rose: fix UAF bugs caused by timer handler

There are UAF bugs in rose_heartbeat_expiry(), rose_timer_expiry()
and rose_idletimer_expiry(). The root cause is that del_timer()
could not stop the timer handler that is running and the refcount
of sock is not managed properly.

One of the UAF bugs is shown below:

    (thread 1)          |        (thread 2)
                        |  rose_bind
                        |  rose_connect
                        |    rose_start_heartbeat
rose_release            |    (wait a time)
  case ROSE_STATE_0     |
  rose_destroy_socket   |  rose_heartbeat_expiry
    rose_stop_heartbeat |
    sock_put(sk)        |    ...
  sock_put(sk) // FREE  |
                        |    bh_lock_sock(sk) // USE

The sock is deallocated by sock_put() in rose_release() and
then used by bh_lock_sock() in rose_heartbeat_expiry().

Although rose_destroy_socket() calls rose_stop_heartbeat(),
it could not stop the timer that is running.

The KASAN report triggered by POC is shown below:

BUG: KASAN: use-after-free in _raw_spin_lock+0x5a/0x110
Write of size 4 at addr ffff88800ae59098 by task swapper/3/0
...
Call Trace:
 <IRQ>
 dump_stack_lvl+0xbf/0xee
 print_address_description+0x7b/0x440
 print_report+0x101/0x230
 ? irq_work_single+0xbb/0x140
 ? _raw_spin_lock+0x5a/0x110
 kasan_report+0xed/0x120
 ? _raw_spin_lock+0x5a/0x110
 kasan_check_range+0x2bd/0x2e0
 _raw_spin_lock+0x5a/0x110
 rose_heartbeat_expiry+0x39/0x370
 ? rose_start_heartbeat+0xb0/0xb0
 call_timer_fn+0x2d/0x1c0
 ? rose_start_heartbeat+0xb0/0xb0
 expire_timers+0x1f3/0x320
 __run_timers+0x3ff/0x4d0
 run_timer_softirq+0x41/0x80
 __do_softirq+0x233/0x544
 irq_exit_rcu+0x41/0xa0
 sysvec_apic_timer_interrupt+0x8c/0xb0
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1b/0x20
RIP: 0010:default_idle+0xb/0x10
RSP: 0018:ffffc9000012fea0 EFLAGS: 00000202
RAX: 000000000000bcae RBX: ffff888006660f00 RCX: 000000000000bcae
RDX: 0000000000000001 RSI: ffffffff843a11c0 RDI: ffffffff843a1180
RBP: dffffc0000000000 R08: dffffc0000000000 R09: ffffed100da36d46
R10: dfffe9100da36d47 R11: ffffffff83cf0950 R12: 0000000000000000
R13: 1ffff11000ccc1e0 R14: ffffffff8542af28 R15: dffffc0000000000
...
Allocated by task 146:
 __kasan_kmalloc+0xc4/0xf0
 sk_prot_alloc+0xdd/0x1a0
 sk_alloc+0x2d/0x4e0
 rose_create+0x7b/0x330
 __sock_create+0x2dd/0x640
 __sys_socket+0xc7/0x270
 __x64_sys_socket+0x71/0x80
 do_syscall_64+0x43/0x90
 entry_SYSCALL_64_after_hwframe+0x46/0xb0

Freed by task 152:
 kasan_set_track+0x4c/0x70
 kasan_set_free_info+0x1f/0x40
 ____kasan_slab_free+0x124/0x190
 kfree+0xd3/0x270
 __sk_destruct+0x314/0x460
 rose_release+0x2fa/0x3b0
 sock_close+0xcb/0x230
 __fput+0x2d9/0x650
 task_work_run+0xd6/0x160
 exit_to_user_mode_loop+0xc7/0xd0
 exit_to_user_mode_prepare+0x4e/0x80
 syscall_exit_to_user_mode+0x20/0x40
 do_syscall_64+0x4f/0x90
 entry_SYSCALL_64_after_hwframe+0x46/0xb0

This patch adds refcount of sock when we use functions
such as rose_start_heartbeat() and so on to start timer,
and decreases the refcount of sock when timer is finished
or deleted by functions such as rose_stop_heartbeat()
and so on. As a result, the UAF bugs could be mitigated.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Tested-by: Duoming Zhou <duoming@zju.edu.cn>
Link: https://lore.kernel.org/r/20220629002640.5693-1-duoming@zju.edu.cn
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Commit author: Duoming Zhou

Vulnerable version (before fix):
 static void rose_idletimer_expiry(struct timer_list *);  void rose_start_heartbeat(struct sock *sk) { 	del_timer(&sk->sk_timer);  	sk->sk_timer.function = rose_heartbeat_expiry; 	sk->sk_timer.expires  = jiffies + 5 * HZ;  	add_timer(&sk->sk_timer); }  void rose_start_t1timer(struct sock *sk) { 	struct rose_sock *rose = rose_sk(sk);  	del_timer(&rose->timer);  	rose->timer.function = rose_timer_expiry; 	rose->timer.expires  = jiffies + rose->t1;  	add_timer(&rose->timer); }  void rose_start_t2timer(struct sock *sk) { 	struct rose_sock *rose = rose_sk(sk);  	del_timer(&rose->timer);  	rose->timer.function = rose_timer_expiry; 	rose->timer.expires  = jiffies + rose->t2;  	add_timer(&rose->timer); }  void rose_start_t3timer(struct sock *sk) { 	struct rose_sock *rose = rose_sk(sk);  	del_timer(&rose->timer);  	rose->timer.function = rose_timer_expiry; 	rose->timer.expires  = jiffies + rose->t3;  	add_timer(&rose->timer); }  void rose_start_hbtimer(struct sock *sk) { 	struct rose_sock *rose = rose_sk(sk);  	del_timer(&rose->timer);  	rose->timer.function = rose_timer_expiry; 	rose->timer.expires  = jiffies + rose->hb;  	add_timer(&rose->timer); }  void rose_start_idletimer(struct sock *sk) { 	struct rose_sock *rose = rose_sk(sk);  	del_timer(&rose->idletimer);  	if (rose->idle > 0) { 		rose->idletimer.function = rose_idletimer_expiry; 		rose->idletimer.expires  = jiffies + rose->idle;  		add_timer(&rose->idletimer); 	} }  void rose_stop_heartbeat(struct sock *sk) { 	del_timer(&sk->sk_timer); }  void rose_stop_timer(struct sock *sk) { 	del_timer(&rose_sk(sk)->timer); }  void rose_stop_idletimer(struct sock *sk) { 	del_timer(&rose_sk(sk)->idletimer); }  static void rose_heartbeat_expiry(struct timer_list *t) static void rose_heartbeat_expiry(struct timer_list *t) 		    (sk->sk_state == TCP_LISTEN && sock_flag(sk, SOCK_DEAD))) { 			bh_unlock_sock(sk); 			rose_destroy_socket(sk); 			return; 		} 		break; static void rose_heartbeat_expiry(struct timer_list *t)  	rose_start_heartbeat(sk); 	bh_unlock_sock(sk); }  static void rose_timer_expiry(struct timer_list *t) static void rose_timer_expiry(struct timer_list *t) 		break; 	} 	bh_unlock_sock(sk); }  static void rose_idletimer_expiry(struct timer_list *t) static void rose_idletimer_expiry(struct timer_list *t) 		sock_set_flag(sk, SOCK_DEAD); 	} 	bh_unlock_sock(sk); }

Fixed version (after fix):
 static void rose_idletimer_expiry(struct timer_list *);  void rose_start_heartbeat(struct sock *sk) { 	sk_stop_timer(sk, &sk->sk_timer);  	sk->sk_timer.function = rose_heartbeat_expiry; 	sk->sk_timer.expires  = jiffies + 5 * HZ;  	sk_reset_timer(sk, &sk->sk_timer, sk->sk_timer.expires); }  void rose_start_t1timer(struct sock *sk) { 	struct rose_sock *rose = rose_sk(sk);  	sk_stop_timer(sk, &rose->timer);  	rose->timer.function = rose_timer_expiry; 	rose->timer.expires  = jiffies + rose->t1;  	sk_reset_timer(sk, &rose->timer, rose->timer.expires); }  void rose_start_t2timer(struct sock *sk) { 	struct rose_sock *rose = rose_sk(sk);  	sk_stop_timer(sk, &rose->timer);  	rose->timer.function = rose_timer_expiry; 	rose->timer.expires  = jiffies + rose->t2;  	sk_reset_timer(sk, &rose->timer, rose->timer.expires); }  void rose_start_t3timer(struct sock *sk) { 	struct rose_sock *rose = rose_sk(sk);  	sk_stop_timer(sk, &rose->timer);  	rose->timer.function = rose_timer_expiry; 	rose->timer.expires  = jiffies + rose->t3;  	sk_reset_timer(sk, &rose->timer, rose->timer.expires); }  void rose_start_hbtimer(struct sock *sk) { 	struct rose_sock *rose = rose_sk(sk);  	sk_stop_timer(sk, &rose->timer);  	rose->timer.function = rose_timer_expiry; 	rose->timer.expires  = jiffies + rose->hb;  	sk_reset_timer(sk, &rose->timer, rose->timer.expires); }  void rose_start_idletimer(struct sock *sk) { 	struct rose_sock *rose = rose_sk(sk);  	sk_stop_timer(sk, &rose->idletimer);  	if (rose->idle > 0) { 		rose->idletimer.function = rose_idletimer_expiry; 		rose->idletimer.expires  = jiffies + rose->idle;  		sk_reset_timer(sk, &rose->idletimer, rose->idletimer.expires); 	} }  void rose_stop_heartbeat(struct sock *sk) { 	sk_stop_timer(sk, &sk->sk_timer); }  void rose_stop_timer(struct sock *sk) { 	sk_stop_timer(sk, &rose_sk(sk)->timer); }  void rose_stop_idletimer(struct sock *sk) { 	sk_stop_timer(sk, &rose_sk(sk)->idletimer); }  static void rose_heartbeat_expiry(struct timer_list *t) static void rose_heartbeat_expiry(struct timer_list *t) 		    (sk->sk_state == TCP_LISTEN && sock_flag(sk, SOCK_DEAD))) { 			bh_unlock_sock(sk); 			rose_destroy_socket(sk); 			sock_put(sk); 			return; 		} 		break; static void rose_heartbeat_expiry(struct timer_list *t)  	rose_start_heartbeat(sk); 	bh_unlock_sock(sk); 	sock_put(sk); }  static void rose_timer_expiry(struct timer_list *t) static void rose_timer_expiry(struct timer_list *t) 		break; 	} 	bh_unlock_sock(sk); 	sock_put(sk); }  static void rose_idletimer_expiry(struct timer_list *t) static void rose_idletimer_expiry(struct timer_list *t) 		sock_set_flag(sk, SOCK_DEAD); 	} 	bh_unlock_sock(sk); 	sock_put(sk); }

Patch:
patch: @@ -31,89 +31,89 @@ static void rose_idletimer_expiry(struct timer_list *);
 
 void rose_start_heartbeat(struct sock *sk)
 {
-	del_timer(&sk->sk_timer);
+	sk_stop_timer(sk, &sk->sk_timer);
 
 	sk->sk_timer.function = rose_heartbeat_expiry;
 	sk->sk_timer.expires  = jiffies + 5 * HZ;
 
-	add_timer(&sk->sk_timer);
+	sk_reset_timer(sk, &sk->sk_timer, sk->sk_timer.expires);
 }
 
 void rose_start_t1timer(struct sock *sk)
 {
 	struct rose_sock *rose = rose_sk(sk);
 
-	del_timer(&rose->timer);
+	sk_stop_timer(sk, &rose->timer);
 
 	rose->timer.function = rose_timer_expiry;
 	rose->timer.expires  = jiffies + rose->t1;
 
-	add_timer(&rose->timer);
+	sk_reset_timer(sk, &rose->timer, rose->timer.expires);
 }
 
 void rose_start_t2timer(struct sock *sk)
 {
 	struct rose_sock *rose = rose_sk(sk);
 
-	del_timer(&rose->timer);
+	sk_stop_timer(sk, &rose->timer);
 
 	rose->timer.function = rose_timer_expiry;
 	rose->timer.expires  = jiffies + rose->t2;
 
-	add_timer(&rose->timer);
+	sk_reset_timer(sk, &rose->timer, rose->timer.expires);
 }
 
 void rose_start_t3timer(struct sock *sk)
 {
 	struct rose_sock *rose = rose_sk(sk);
 
-	del_timer(&rose->timer);
+	sk_stop_timer(sk, &rose->timer);
 
 	rose->timer.function = rose_timer_expiry;
 	rose->timer.expires  = jiffies + rose->t3;
 
-	add_timer(&rose->timer);
+	sk_reset_timer(sk, &rose->timer, rose->timer.expires);
 }
 
 void rose_start_hbtimer(struct sock *sk)
 {
 	struct rose_sock *rose = rose_sk(sk);
 
-	del_timer(&rose->timer);
+	sk_stop_timer(sk, &rose->timer);
 
 	rose->timer.function = rose_timer_expiry;
 	rose->timer.expires  = jiffies + rose->hb;
 
-	add_timer(&rose->timer);
+	sk_reset_timer(sk, &rose->timer, rose->timer.expires);
 }
 
 void rose_start_idletimer(struct sock *sk)
 {
 	struct rose_sock *rose = rose_sk(sk);
 
-	del_timer(&rose->idletimer);
+	sk_stop_timer(sk, &rose->idletimer);
 
 	if (rose->idle > 0) {
 		rose->idletimer.function = rose_idletimer_expiry;
 		rose->idletimer.expires  = jiffies + rose->idle;
 
-		add_timer(&rose->idletimer);
+		sk_reset_timer(sk, &rose->idletimer, rose->idletimer.expires);
 	}
 }
 
 void rose_stop_heartbeat(struct sock *sk)
 {
-	del_timer(&sk->sk_timer);
+	sk_stop_timer(sk, &sk->sk_timer);
 }
 
 void rose_stop_timer(struct sock *sk)
 {
-	del_timer(&rose_sk(sk)->timer);
+	sk_stop_timer(sk, &rose_sk(sk)->timer);
 }
 
 void rose_stop_idletimer(struct sock *sk)
 {
-	del_timer(&rose_sk(sk)->idletimer);
+	sk_stop_timer(sk, &rose_sk(sk)->idletimer);
 }
 
 static void rose_heartbeat_expiry(struct timer_list *t)
@@ -130,6 +130,7 @@ static void rose_heartbeat_expiry(struct timer_list *t)
 		    (sk->sk_state == TCP_LISTEN && sock_flag(sk, SOCK_DEAD))) {
 			bh_unlock_sock(sk);
 			rose_destroy_socket(sk);
+			sock_put(sk);
 			return;
 		}
 		break;
@@ -152,6 +153,7 @@ static void rose_heartbeat_expiry(struct timer_list *t)
 
 	rose_start_heartbeat(sk);
 	bh_unlock_sock(sk);
+	sock_put(sk);
 }
 
 static void rose_timer_expiry(struct timer_list *t)
@@ -181,6 +183,7 @@ static void rose_timer_expiry(struct timer_list *t)
 		break;
 	}
 	bh_unlock_sock(sk);
+	sock_put(sk);
 }
 
 static void rose_idletimer_expiry(struct timer_list *t)
@@ -205,4 +208,5 @@ static void rose_idletimer_expiry(struct timer_list *t)
 		sock_set_flag(sk, SOCK_DEAD);
 	}
 	bh_unlock_sock(sk);
+	sock_put(sk);
 }
path: net/rose/rose_timer.c