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From:   Ruihan Li <lrh2000@pku.edu.cn>
To:     linux-bluetooth@vger.kernel.org
Cc:     Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        Ruihan Li <lrh2000@pku.edu.cn>, stable@vger.kernel.org
Subject: [PATCH] bluetooth: Perform careful capability checks in hci_sock_ioctl()
Date:   Sun, 16 Apr 2023 16:14:04 +0800
Message-Id: <20230416081404.8227-1-lrh2000@pku.edu.cn>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Previously, capability was checked using capable(), which verified that the
caller of the ioctl system call had the required capability. In addition,
the result of the check would be stored in the HCI_SOCK_TRUSTED flag,
making it persistent for the socket.

However, malicious programs can abuse this approach by deliberately sharing
an HCI socket with a privileged task. The HCI socket will be marked as
trusted when the privileged task occasionally makes an ioctl call.

This problem can be solved by using sk_capable() to check capability, which
ensures that not only the current task but also the socket opener has the
specified capability, thus reducing the risk of privilege escalation
through the previously identified vulnerability.

Cc: stable@vger.kernel.org
Fixes: f81f5b2db869 ("Bluetooth: Send control open and close messages for HCI raw sockets")
Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn>
---
 net/bluetooth/hci_sock.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
index 065812232..f597fe0db 100644
--- a/net/bluetooth/hci_sock.c
+++ b/net/bluetooth/hci_sock.c
@@ -1003,7 +1003,14 @@ static int hci_sock_ioctl(struct socket *sock, unsigned int cmd,
 	if (hci_sock_gen_cookie(sk)) {
 		struct sk_buff *skb;
 
-		if (capable(CAP_NET_ADMIN))
+		/* Perform careful checks before setting the HCI_SOCK_TRUSTED
+		 * flag. Make sure that not only the current task but also
+		 * the socket opener has the required capability, since
+		 * privileged programs can be tricked into making ioctl calls
+		 * on HCI sockets, and the socket should not be marked as
+		 * trusted simply because the ioctl caller is privileged.
+		 */
+		if (sk_capable(sk, CAP_NET_ADMIN))
 			hci_sock_set_flag(sk, HCI_SOCK_TRUSTED);
 
 		/* Send event to monitor */
-- 
2.40.0