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Bluetooth: sco: Fix lock_sock() blockage by memcpy_from_msg()
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The sco_send_frame() also takes lock_sock() during memcpy_from_msg()
call that may be endlessly blocked by a task with userfaultd
technique, and this will result in a hung task watchdog trigger.

Just like the similar fix for hci_sock_sendmsg() in commit
92c685d ("Bluetooth: reorganize functions..."), this patch moves
the  memcpy_from_msg() out of lock_sock() for addressing the hang.

This should be the last piece for fixing CVE-2021-3640 after a few
already queued fixes.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
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tiwai authored and holtmann committed Aug 30, 2021
1 parent 927ac8d commit 99c23da
Showing 1 changed file with 16 additions and 8 deletions.
24 changes: 16 additions & 8 deletions net/bluetooth/sco.c
Original file line number Diff line number Diff line change
Expand Up @@ -280,7 +280,8 @@ static int sco_connect(struct hci_dev *hdev, struct sock *sk)
return err;
}

static int sco_send_frame(struct sock *sk, struct msghdr *msg, int len)
static int sco_send_frame(struct sock *sk, void *buf, int len,
unsigned int msg_flags)
{
struct sco_conn *conn = sco_pi(sk)->conn;
struct sk_buff *skb;
Expand All @@ -292,15 +293,11 @@ static int sco_send_frame(struct sock *sk, struct msghdr *msg, int len)

BT_DBG("sk %p len %d", sk, len);

skb = bt_skb_send_alloc(sk, len, msg->msg_flags & MSG_DONTWAIT, &err);
skb = bt_skb_send_alloc(sk, len, msg_flags & MSG_DONTWAIT, &err);
if (!skb)
return err;

if (memcpy_from_msg(skb_put(skb, len), msg, len)) {
kfree_skb(skb);
return -EFAULT;
}

memcpy(skb_put(skb, len), buf, len);
hci_send_sco(conn->hcon, skb);

return len;
Expand Down Expand Up @@ -725,6 +722,7 @@ static int sco_sock_sendmsg(struct socket *sock, struct msghdr *msg,
size_t len)
{
struct sock *sk = sock->sk;
void *buf;
int err;

BT_DBG("sock %p, sk %p", sock, sk);
Expand All @@ -736,14 +734,24 @@ static int sco_sock_sendmsg(struct socket *sock, struct msghdr *msg,
if (msg->msg_flags & MSG_OOB)
return -EOPNOTSUPP;

buf = kmalloc(len, GFP_KERNEL);
if (!buf)
return -ENOMEM;

if (memcpy_from_msg(buf, msg, len)) {
kfree(buf);
return -EFAULT;
}

lock_sock(sk);

if (sk->sk_state == BT_CONNECTED)
err = sco_send_frame(sk, msg, len);
err = sco_send_frame(sk, buf, len, msg->msg_flags);
else
err = -ENOTCONN;

release_sock(sk);
kfree(buf);
return err;
}

Expand Down

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