CVE-2022-2318: Use After Free (CWE-416)
value: 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.
CWE description: The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
CVSS v3 base score: 5.5
Published: 2022-07-06T19:15Z
Repository: https://github.com/torvalds/linux
Language: C
Files changed: net/rose/rose_timer.c
Commit date: 2022-06-30 11:07:30 +0200
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>

Diff: diff --git a/net/rose/rose_timer.c b/net/rose/rose_timer.c
index b3138fc2e552..f06ddbed3fed 100644
--- a/net/rose/rose_timer.c
+++ b/net/rose/rose_timer.c
@@ -29,93 +29,93 @@ static void rose_heartbeat_expiry(struct timer_list *t);
 static void rose_timer_expiry(struct timer_list *);
 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)
 {
 	struct sock *sk = from_timer(sk, t, sk_timer);
@@ -128,10 +128,11 @@ static void rose_heartbeat_expiry(struct timer_list *t)
 		   is accepted() it isn't 'dead' so doesn't get removed. */
 		if (sock_flag(sk, SOCK_DESTROY) ||
 		    (sk->sk_state == TCP_LISTEN && sock_flag(sk, SOCK_DEAD))) {
 			bh_unlock_sock(sk);
 			rose_destroy_socket(sk);
+			sock_put(sk);
 			return;
 		}
 		break;
 
 	case ROSE_STATE_3:
@@ -150,10 +151,11 @@ static void rose_heartbeat_expiry(struct timer_list *t)
 		break;
 	}
 
 	rose_start_heartbeat(sk);
 	bh_unlock_sock(sk);
+	sock_put(sk);
 }
 
 static void rose_timer_expiry(struct timer_list *t)
 {
 	struct rose_sock *rose = from_timer(rose, t, timer);
@@ -179,10 +181,11 @@ static void rose_timer_expiry(struct timer_list *t)
 			rose_enquiry_response(sk);
 		}
 		break;
 	}
 	bh_unlock_sock(sk);
+	sock_put(sk);
 }
 
 static void rose_idletimer_expiry(struct timer_list *t)
 {
 	struct rose_sock *rose = from_timer(rose, t, idletimer);
@@ -203,6 +206,7 @@ static void rose_idletimer_expiry(struct timer_list *t)
 	if (!sock_flag(sk, SOCK_DEAD)) {
 		sk->sk_state_change(sk);
 		sock_set_flag(sk, SOCK_DEAD);
 	}
 	bh_unlock_sock(sk);
+	sock_put(sk);
 }

Vulnerable code: 	del_timer(&sk->sk_timer);
	add_timer(&sk->sk_timer);
	del_timer(&rose->timer);
	add_timer(&rose->timer);
	del_timer(&rose->timer);
	add_timer(&rose->timer);
	del_timer(&rose->timer);
	add_timer(&rose->timer);
	del_timer(&rose->timer);
	add_timer(&rose->timer);
	del_timer(&rose->idletimer);
		add_timer(&rose->idletimer);
	del_timer(&sk->sk_timer);
	del_timer(&rose_sk(sk)->timer);
	del_timer(&rose_sk(sk)->idletimer);
Fixed code: 	sk_stop_timer(sk, &sk->sk_timer);
	sk_reset_timer(sk, &sk->sk_timer, sk->sk_timer.expires);
	sk_stop_timer(sk, &rose->timer);
	sk_reset_timer(sk, &rose->timer, rose->timer.expires);
	sk_stop_timer(sk, &rose->timer);
	sk_reset_timer(sk, &rose->timer, rose->timer.expires);
	sk_stop_timer(sk, &rose->timer);
	sk_reset_timer(sk, &rose->timer, rose->timer.expires);
	sk_stop_timer(sk, &rose->timer);
	sk_reset_timer(sk, &rose->timer, rose->timer.expires);
	sk_stop_timer(sk, &rose->idletimer);
		sk_reset_timer(sk, &rose->idletimer, rose->idletimer.expires);
	sk_stop_timer(sk, &sk->sk_timer);
	sk_stop_timer(sk, &rose_sk(sk)->timer);
	sk_stop_timer(sk, &rose_sk(sk)->idletimer);
			sock_put(sk);
	sock_put(sk);
	sock_put(sk);
	sock_put(sk);