[PATCH 5.15/5.10/5.4/4.19 1/1] pppoe: Fix memory leak in pppoe_sendmsg()

[Gavrilov Ilia <Ilia.Gavrilov@xxxxxxxxxxx>]

From: Gavrilov Ilia <Ilia.Gavrilov@xxxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=6bdfd184eac7709e5cc9
Signed-off-by: Gavrilov Ilia <Ilia.Gavrilov@xxxxxxxxxxx>
Reviewed-by: Guillaume Nault <gnault@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240214085814.3894917-1-Ilia.Gavrilov@xxxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
---
 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;
 }

--
2.39.2


С уважением,
Илья Гаврилов
Ведущий программист
Отдел разработки
АО "ИнфоТеКС" в г. Санкт-Петербург
127287, г. Москва, Старый Петровско-Разумовский проезд, дом 1/23, стр. 1
T: +7 495 737-61-92 ( доб. 4921)
Ф: +7 495 737-72-78


Ilia.Gavrilov@xxxxxxxxxxx
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