[PATCH] can: j1939: return 0 instead of user value in j1939_sk_setsockopt_flag()

[Hui Peng]

In `j1939_sk_setsockopt_flag()`, after copying the integer option value
`tmp` from userspace and updating `jsk->state`, the function returns
`tmp` instead of `0`.

If a caller passes a negative integer (e.g., `-1`) to enable
`SO_J1939_BROADCAST` or `SO_J1939_PROMISC`, `if (tmp)` sets `jsk->state
|= flag` and then returns the negative value as an error code from
`setsockopt()`. If a caller passes a positive non-zero integer (e.g.,
`1`), `setsockopt()` violates POSIX by returning `1` instead of `0`.

Return `0` on success in `j1939_sk_setsockopt_flag()`.

Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@xxxxxxxxx>

---
 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 50a598ef5fd4..1d4af472de4a 100644
--- a/net/can/j1939/socket.c
+++ b/net/can/j1939/socket.c
@@ -688,7 +688,7 @@ static int j1939_sk_setsockopt_flag(struct j1939_sock *jsk, sockptr_t optval,
 	else
 		jsk->state &= ~flag;
 	release_sock(&jsk->sk);
-	return tmp;
+	return 0;
 }
 
 static int j1939_sk_setsockopt(struct socket *sock, int level, int optname,
-- 
2.55.0.1082.g2b9226bbc0-goog