linux-kernel - [PATCH 4.14 06/23] ax25: Fix NULL pointer dereference in ax25_kill_by

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Date:   Mon, 14 Mar 2022 12:34:19 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Thomas Osterried <thomas@...erried.de>,
        Duoming Zhou <duoming@....edu.cn>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 06/23] ax25: Fix NULL pointer dereference in ax25_kill_by_device

From: Duoming Zhou <duoming@....edu.cn>

[ Upstream commit 71171ac8eb34ce7fe6b3267dce27c313ab3cb3ac ]

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@...erried.de>
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 | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index 36d2e1dfa1e6..466f9e3883c8 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -90,6 +90,13 @@ 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);
-- 
2.34.1