Commit dc34ebd5 authored by Gavrilov Ilia's avatar Gavrilov Ilia Committed by Jakub Kicinski
Browse files

pppoe: Fix memory leak in pppoe_sendmsg() 

syzbot reports a memory leak in pppoe_sendmsg [1].

The problem is in the pppoe_recvmsg() function that handles errors
in the wrong order. For the skb_recv_datagram() function, check
the pointer to skb for NULL first, and then check the 'error' variable,
because the skb_recv_datagram() function can set 'error'
to -EAGAIN in a loop but return a correct pointer to socket buffer
after a number of attempts, though 'error' remains set to -EAGAIN.

skb_recv_datagram
      __skb_recv_datagram          // Loop. if (err == -EAGAIN) then
                                   // go to the next loop iteration
          __skb_try_recv_datagram  // if (skb != NULL) then return 'skb'
                                   // else if a signal is received then
                                   // return -EAGAIN

Found by InfoTeCS on behalf of Linux Verification Center
(linuxtesting.org) with Syzkaller.

Link: https://syzkaller.appspot.com/bug?extid=6bdfd184eac7709e5cc9

 [1]

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Reported-by: default avatar <syzbot+6bdfd184eac7709e5cc9@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=6bdfd184eac7709e5cc9


Signed-off-by: default avatarGavrilov Ilia <Ilia.Gavrilov@infotecs.ru>
Reviewed-by: default avatarGuillaume Nault <gnault@redhat.com>
Link: https://lore.kernel.org/r/20240214085814.3894917-1-Ilia.Gavrilov@infotecs.ru


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 4e45170d

drivers/net/ppp/pppoe.c

+9 −14
Original line number Diff line number Diff line
@@ -1007,26 +1007,21 @@ static int pppoe_recvmsg(struct socket *sock, struct msghdr *m, 
	struct sk_buff *skb;

	int error = 0;



	if (sk->sk_state & PPPOX_BOUND) {

		error = -EIO;

		goto end;

	}

	if (sk->sk_state & PPPOX_BOUND)

		return -EIO;



	skb = skb_recv_datagram(sk, flags, &error);

	if (error < 0)

		goto end;

	if (!skb)

		return error;



	if (skb) {

	total_len = min_t(size_t, total_len, skb->len);

	error = skb_copy_datagram_msg(skb, 0, m, total_len);

	if (error == 0) {

		consume_skb(skb);

		return total_len;

	}

	}



	kfree_skb(skb);

end:

	return error;

}