CVE-2022-1199 (published 2022-08-29T15:15Z)

A flaw was found in the Linux kernel. This flaw allows an attacker to crash the Linux kernel by simulating amateur radio from the user space, resulting in a null-ptr-deref vulnerability and a use-after-free vulnerability.

CVSS v3 base score: 7.5, HIGH (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Weakness information:
cwe_id: CWE-416
cwe_name: Use After Free
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 Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
extended_description: 
             
             
             
			 
             
             
         
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Duoming Zhou
author_date: 2022-01-28 12:47:15+08:00
msg: ax25: improve the incomplete fix to avoid UAF and NPD bugs

The previous commit 1ade48d0c27d ("ax25: NPD bug when detaching
AX25 device") introduce lock_sock() into ax25_kill_by_device to
prevent NPD bug. But the concurrency NPD or UAF bug will occur,
when lock_sock() or release_sock() dereferences the ax25_cb->sock.

The NULL pointer dereference bug can be shown as below:

ax25_kill_by_device()        | ax25_release()
                             |   ax25_destroy_socket()
                             |     ax25_cb_del()
  ...                        |     ...
                             |     ax25->sk=NULL;
  lock_sock(s->sk); //(1)    |
  s->ax25_dev = NULL;        |     ...
  release_sock(s->sk); //(2) |
  ...                        |

The root cause is that the sock is set to null before dereference
site (1) or (2). Therefore, this patch extracts the ax25_cb->sock
in advance, and uses ax25_list_lock to protect it, which can synchronize
with ax25_cb_del() and ensure the value of sock is not null before
dereference sites.

The concurrency UAF bug can be shown as below:

ax25_kill_by_device()        | ax25_release()
                             |   ax25_destroy_socket()
  ...                        |   ...
                             |   sock_put(sk); //FREE
  lock_sock(s->sk); //(1)    |
  s->ax25_dev = NULL;        |   ...
  release_sock(s->sk); //(2) |
  ...                        |

The root cause is that the sock is released before dereference
site (1) or (2). Therefore, this patch uses sock_hold() to increase
the refcount of sock and uses ax25_list_lock to protect it, which
can synchronize with ax25_cb_del() in ax25_destroy_socket() and
ensure the sock wil not be released before dereference sites.

Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: af_ax25.c
change_type: ModificationType.MODIFY
diff: @@ -77,6 +77,7 @@ static void ax25_kill_by_device(struct net_device *dev)
 {
 	ax25_dev *ax25_dev;
 	ax25_cb *s;
+	struct sock *sk;
 
 	if ((ax25_dev = ax25_dev_ax25dev(dev)) == NULL)
 		return;
@@ -85,13 +86,15 @@ static void ax25_kill_by_device(struct net_device *dev)
 again:
 	ax25_for_each(s, &ax25_list) {
 		if (s->ax25_dev == ax25_dev) {
+			sk = s->sk;
+			sock_hold(sk);
 			spin_unlock_bh(&ax25_list_lock);
-			lock_sock(s->sk);
+			lock_sock(sk);
 			s->ax25_dev = NULL;
-			release_sock(s->sk);
+			release_sock(sk);
 			ax25_disconnect(s, ENETUNREACH);
 			spin_lock_bh(&ax25_list_lock);
-
+			sock_put(sk);
 			/* The entry could have been deleted from the
 			 * list meanwhile and thus the next pointer is
 			 * no longer valid.  Play it safe and restart

programming_language: C
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Duoming Zhou
author_date: 2022-02-08 23:40:00+08:00
msg: ax25: fix NPD bug in ax25_disconnect

The ax25_disconnect() in ax25_kill_by_device() is not
protected by any locks, thus there is a race condition
between ax25_disconnect() and ax25_destroy_socket().
when ax25->sk is assigned as NULL by ax25_destroy_socket(),
a NULL pointer dereference bug will occur if site (1) or (2)
dereferences ax25->sk.

ax25_kill_by_device()                | ax25_release()
  ax25_disconnect()                  |   ax25_destroy_socket()
    ...                              |
    if(ax25->sk != NULL)             |     ...
      ...                            |     ax25->sk = NULL;
      bh_lock_sock(ax25->sk); //(1)  |     ...
      ...                            |
      bh_unlock_sock(ax25->sk); //(2)|

This patch moves ax25_disconnect() into lock_sock(), which can
synchronize with ax25_destroy_socket() in ax25_release().

Fail log:
===============================================================
BUG: kernel NULL pointer dereference, address: 0000000000000088
...
RIP: 0010:_raw_spin_lock+0x7e/0xd0
...
Call Trace:
ax25_disconnect+0xf6/0x220
ax25_device_event+0x187/0x250
raw_notifier_call_chain+0x5e/0x70
dev_close_many+0x17d/0x230
rollback_registered_many+0x1f1/0x950
unregister_netdevice_queue+0x133/0x200
unregister_netdev+0x13/0x20
...

Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: af_ax25.c
change_type: ModificationType.MODIFY
diff: @@ -92,8 +92,8 @@ static void ax25_kill_by_device(struct net_device *dev)
 			lock_sock(sk);
 			s->ax25_dev = NULL;
 			ax25_dev_put(ax25_dev);
-			release_sock(sk);
 			ax25_disconnect(s, ENETUNREACH);
+			release_sock(sk);
 			spin_lock_bh(&ax25_list_lock);
 			sock_put(sk);
 			/* The entry could have been deleted from the

programming_language: C
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Duoming Zhou
author_date: 2022-03-08 16:12:23+08:00
msg: ax25: Fix NULL pointer dereference in ax25_kill_by_device

When two ax25 devices attempted to establish connection, the requester use ax25_create(),
ax25_bind() and ax25_connect() to initiate connection. The receiver use ax25_rcv() to
accept connection and use ax25_create_cb() in ax25_rcv() to create ax25_cb, but the
ax25_cb->sk is NULL. When the receiver is detaching, a NULL pointer dereference bug
caused by sock_hold(sk) in ax25_kill_by_device() will happen. The corresponding
fail log is shown below:

===============================================================
BUG: KASAN: null-ptr-deref in ax25_device_event+0xfd/0x290
Call Trace:
...
ax25_device_event+0xfd/0x290
raw_notifier_call_chain+0x5e/0x70
dev_close_many+0x174/0x220
unregister_netdevice_many+0x1f7/0xa60
unregister_netdevice_queue+0x12f/0x170
unregister_netdev+0x13/0x20
mkiss_close+0xcd/0x140
tty_ldisc_release+0xc0/0x220
tty_release_struct+0x17/0xa0
tty_release+0x62d/0x670
...

This patch add condition check in ax25_kill_by_device(). If s->sk is
NULL, it will goto if branch to kill device.

Fixes: 4e0f718daf97 ("ax25: improve the incomplete fix to avoid UAF and NPD bugs")
Reported-by: Thomas Osterried <thomas@osterried.de>
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: af_ax25.c
change_type: ModificationType.MODIFY
diff: @@ -87,6 +87,13 @@ static void ax25_kill_by_device(struct net_device *dev)
 	ax25_for_each(s, &ax25_list) {
 		if (s->ax25_dev == ax25_dev) {
 			sk = s->sk;
+			if (!sk) {
+				spin_unlock_bh(&ax25_list_lock);
+				s->ax25_dev = NULL;
+				ax25_disconnect(s, ENETUNREACH);
+				spin_lock_bh(&ax25_list_lock);
+				goto again;
+			}
 			sock_hold(sk);
 			spin_unlock_bh(&ax25_list_lock);
 			lock_sock(sk);

programming_language: C