Re: [PATCH v2] Bluetooth: af_bluetooth: Fix Use-After-Free in bt_sock_recvmsg

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Hi Hyunwoo,

I've been looking into a few CVEs, the one of interest in this case is CVE-2024-21803.

There seems to be little publicly available information about this CVE, however the title of this patch and the affected kernel range suggest this may be a fix for this CVE.

Would you be able to clarify whether this is a fix for CVE-2024-21803?



On 09/12/2023 10:55, Hyunwoo Kim wrote:
This can cause a race with bt_sock_ioctl() because
bt_sock_recvmsg() gets the skb from sk->sk_receive_queue
and then frees it without holding lock_sock.
A use-after-free for a skb occurs with the following flow.
bt_sock_recvmsg() -> skb_recv_datagram() -> skb_free_datagram()
bt_sock_ioctl() -> skb_peek()
Add lock_sock to bt_sock_recvmsg() to fix this issue.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Hyunwoo Kim <v4bel@xxxxxxxxx>
v1 -> v2: Remove duplicate release_sock()s
  net/bluetooth/af_bluetooth.c | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
index 336a76165454..b93464ac3517 100644
--- a/net/bluetooth/af_bluetooth.c
+++ b/net/bluetooth/af_bluetooth.c
@@ -309,11 +309,14 @@ int bt_sock_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
  	if (flags & MSG_OOB)
  		return -EOPNOTSUPP;
+ lock_sock(sk);
  	skb = skb_recv_datagram(sk, flags, &err);
  	if (!skb) {
  		if (sk->sk_shutdown & RCV_SHUTDOWN)
-			return 0;
+			err = 0;
+ release_sock(sk);
  		return err;
@@ -343,6 +346,8 @@ int bt_sock_recvmsg(struct socket *sock, struct msghdr *msg, size_t len, skb_free_datagram(sk, skb); + release_sock(sk);
  	if (flags & MSG_TRUNC)
  		copied = skblen;

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