When writing to the disable_policy sysctl, if proc_dointvec() fails to
parse the input, it returns a negative error code. The current
implementation is resetting the position argument even if an error
occurred during proc_dointvec() and not only during sysctl restart.

Fix this by checking the return value of proc_dointvec() and returning
early on failure.

Fixes: df789fe75206 ("ipv6: Provide ipv6 version of "disable_policy" sysctl")
Reviewed-by: Nicolas Dichtel <redacted>
Signed-off-by: Fernando Fernandez Mancera <redacted>
---
 net/ipv6/addrconf.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index d23a89b07eed..5d96cbf76134 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c

@@ -6769,6 +6769,8 @@ static int addrconf_sysctl_disable_policy(const struct ctl_table *ctl, int write
 	lctl = *ctl;
 	lctl.data = &val;
 	ret = proc_dointvec(&lctl, write, buffer, lenp, ppos);
+	if (ret)
+		return ret;
 
 	if (write && (*valp != val))
 		ret = addrconf_disable_policy(ctl, valp, val);

-- 
2.54.0