| From c0eaf9d7de650ebe2bfb222b1ce9acf248680433 Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Fri, 28 Jan 2022 12:47:15 +0800 |
| Subject: ax25: improve the incomplete fix to avoid UAF and NPD bugs |
| |
| From: Duoming Zhou <duoming@zju.edu.cn> |
| |
| [ Upstream commit 4e0f718daf97d47cf7dec122da1be970f145c809 ] |
| |
| 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> |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| net/ax25/af_ax25.c | 9 ++++++--- |
| 1 file changed, 6 insertions(+), 3 deletions(-) |
| |
| diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c |
| index 1f84d41e22c36..184af6da0defc 100644 |
| --- a/net/ax25/af_ax25.c |
| +++ b/net/ax25/af_ax25.c |
| @@ -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 |
| -- |
| 2.34.1 |
| |