[PATCH net-next v2 4/6] l2tp: fix incorrect parameter validation in the pppol2tp_getsockopt() function

[Gavrilov Ilia]

The 'len' variable can't be negative when assigned the result of
'min_t' because all 'min_t' parameters are cast to unsigned int,
and then the minimum one is chosen.

To fix the logic, check 'len' as read from 'optlen',
where the types of relevant variables are (signed) int.

Fixes: 3557baabf280 ("[L2TP]: PPP over L2TP driver core")
Reviewed-by: Tom Parkin <tparkin@xxxxxxxxxxx>
Signed-off-by: Gavrilov Ilia <Ilia.Gavrilov@xxxxxxxxxxx>
---
V2:
 - reword the patch description
 net/l2tp/l2tp_ppp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index f011af6601c9..6146e4e67bbb 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -1356,11 +1356,11 @@ static int pppol2tp_getsockopt(struct socket *sock, int level, int optname,
 	if (get_user(len, optlen))
 		return -EFAULT;
 
-	len = min_t(unsigned int, len, sizeof(int));
-
 	if (len < 0)
 		return -EINVAL;
 
+	len = min_t(unsigned int, len, sizeof(int));
+
 	err = -ENOTCONN;
 	if (!sk->sk_user_data)
 		goto end;
-- 
2.39.2