If optval != NULL and optlen = 0 are specified for SO_J1939_FILTER in
j1939_sk_setsockopt(), memdup_sockptr() will return ZERO_PTR for 0 size
allocation. The new filter will be mistakenly assigned ZERO_PTR.
This patch checks for optlen != 0 and filter will be assigned NULL
in case of optlen = 0.

Fixes: a7b75c5a8c41 ("net: pass a sockptr_t into ->setsockopt")
Signed-off-by: Norbert Slusarek <redacted>

---
 net/can/j1939/socket.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c
index 56aa66147d5a..ff20cb629200 100644
--- a/net/can/j1939/socket.c
+++ b/net/can/j1939/socket.c

@@ -673,7 +673,7 @@ static int j1939_sk_setsockopt(struct socket *sock, int level, int optname,

 	switch (optname) {
 	case SO_J1939_FILTER:
-		if (!sockptr_is_null(optval)) {
+		if (!sockptr_is_null(optval) && optlen != 0) {
 			struct j1939_filter *f;
 			int c;

--

2.30.2