From: Gavrilov Ilia Ilia.Gavrilov@infotecs.ru

commit dc34ebd5c018b0edf47f39d11083ad8312733034 upstream.

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: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+6bdfd184eac7709e5cc9@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=6bdfd184eac7709e5cc9 Signed-off-by: Gavrilov Ilia Ilia.Gavrilov@infotecs.ru Reviewed-by: Guillaume Nault gnault@redhat.com Link: https://lore.kernel.org/r/20240214085814.3894917-1-Ilia.Gavrilov@infotecs.ru Signed-off-by: Jakub Kicinski kuba@kernel.org --- drivers/net/ppp/pppoe.c | 23 +++++++++-------------- 1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c index d7f50b835050..70e29e1ac4c8 100644 --- a/drivers/net/ppp/pppoe.c +++ b/drivers/net/ppp/pppoe.c @@ -983,27 +983,22 @@ 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 & ~MSG_DONTWAIT, flags & MSG_DONTWAIT, &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; - } + 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; }