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Bluetooth: Fix bt_sock_recvmsg return value

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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>
This commit is contained in:
Denis Kenzior 2016-06-27 11:01:12 -05:00 committed by Marcel Holtmann
parent 1c5bf998b3
commit b5f34f9420
1 changed files with 5 additions and 0 deletions
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5
net/bluetooth/af_bluetooth.c
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@ -215,6 +215,7 @@ int bt_sock_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
struct sock *sk = sock->sk;
struct sk_buff *skb;
size_t copied;
size_t skblen;
int err;
BT_DBG("sock %p sk %p len %zu", sock, sk, len);
@ -230,6 +231,7 @@ int bt_sock_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
return err;
}
skblen = skb->len;
copied = skb->len;
if (len < copied) {
msg->msg_flags |= MSG_TRUNC;
@ -248,6 +250,9 @@ int bt_sock_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
skb_free_datagram(sk, skb);
if (msg->msg_flags & MSG_TRUNC)
copied = skblen;
return err ? : copied;
}
EXPORT_SYMBOL(bt_sock_recvmsg);