Commit 83871f8c authored Jun 27, 2016 by Denis Kenzior Committed by Marcel Holtmann Jul 08, 2016

Bluetooth: Fix hci_sock_recvmsg return value



If recvmsg is called with a destination buffer that is too small to
receive the contents of skb in its entirety, the return value from
recvmsg was inconsistent with common SOCK_SEQPACKET or SOCK_DGRAM
semantics.

If destination buffer provided by userspace is too small (e.g. len <
copied), then MSG_TRUNC flag is set and copied is returned.  Instead, it
should return the length of the message, which is consistent with how
other datagram based sockets act.  Quoting 'man recv':

"All  three calls return the length of the message on successful comple‐
tion.  If a message is too long to fit in the supplied  buffer,  excess
bytes  may  be discarded depending on the type of socket the message is
received from."

and

"MSG_TRUNC (since Linux 2.2)

    For   raw   (AF_PACKET),   Internet   datagram   (since    Linux
    2.4.27/2.6.8),  netlink  (since Linux 2.6.22), and UNIX datagram
    (since Linux 3.4) sockets: return the real length of the packet
    or datagram, even when it was longer than the passed buffer."

Signed-off-by: Denis Kenzior <denkenz@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

parent b5f34f94

net/bluetooth/hci_sock.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -1048,6 +1048,7 @@ static int hci_sock_recvmsg(struct socket sock, struct msghdr msg,
		struct sock *sk = sock->sk;
		struct sk_buff *skb;
		int copied, err;
		unsigned int skblen;

		BT_DBG("sock %p, sk %p", sock, sk);

		@@ -1064,6 +1065,7 @@ static int hci_sock_recvmsg(struct socket sock, struct msghdr msg,
		if (!skb)
		return err;

		skblen = skb->len;
		copied = skb->len;
		if (len < copied) {
		msg->msg_flags \|= MSG_TRUNC;
		@@ -1089,6 +1091,9 @@ static int hci_sock_recvmsg(struct socket sock, struct msghdr msg,

		skb_free_datagram(sk, skb);

		if (msg->msg_flags & MSG_TRUNC)
		copied = skblen;

		return err ? : copied;
		}

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