l2tp: fix incorrect parameter validation in the pppol2tp_getsockopt() function

[ Upstream commit 955e9876ba4ee26eeaab1b13517f5b2c88e73d55 ]

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@katalix.com>
Signed-off-by: Gavrilov Ilia <Ilia.Gavrilov@infotecs.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index 9cef8e080f644601afdde9ace7d8bd3eb9f42985..55de42b000d8a204d87405acbd6c5e850ae077ee 100644 (file)
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -1357,11 +1357,11 @@ 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;