[PATCH net-next v2 5/6] net: kcm: fix incorrect parameter validation in the kcm_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: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module")
Signed-off-by: Gavrilov Ilia <Ilia.Gavrilov@xxxxxxxxxxx>
---
 net/kcm/kcmsock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 1184d40167b8..eda933c09792 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1152,10 +1152,11 @@ static int kcm_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));
+
 	switch (optname) {
 	case KCM_RECV_DISABLE:
 		val = kcm->rx_disabled;
-- 
2.39.2