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Date: Wed, 9 Feb 2022 13:42:53 -0500 From: Sasha Levin <sashal@...nel.org> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org Cc: Duoming Zhou <duoming@....edu.cn>, "David S . Miller" <davem@...emloft.net>, Sasha Levin <sashal@...nel.org>, jreuter@...na.de, kuba@...nel.org, linux-hams@...r.kernel.org, netdev@...r.kernel.org Subject: [PATCH AUTOSEL 5.4 07/15] ax25: improve the incomplete fix to avoid UAF and NPD bugs From: Duoming Zhou <duoming@....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@....edu.cn> Signed-off-by: David S. Miller <davem@...emloft.net> Signed-off-by: Sasha Levin <sashal@...nel.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
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