genetlink: make policy common to family

Since maxattr is common, the policy can't really differ sanely,
so make it common as well.

The only user that did in fact manage to make a non-common policy
is taskstats, which has to be really careful about it (since it's
still using a common maxattr!). This is no longer supported, but
we can fake it using pre_doit.

This reduces the size of e.g. nl80211.o (which has lots of commands):

   text	   data	    bss	    dec	    hex	filename
 398745	  14323	   2240	 415308	  6564c	net/wireless/nl80211.o (before)
 397913	  14331	   2240	 414484	  65314	net/wireless/nl80211.o (after)
--------------------------------
   -832      +8       0    -824

Which is obviously just 8 bytes for each command, and an added 8
bytes for the new policy pointer. I'm not sure why the ops list is
counted as .text though.

Most of the code transformations were done using the following spatch:
    @ops@
    identifier OPS;
    expression POLICY;
    @@
    struct genl_ops OPS[] = {
    ...,
     {
    -	.policy = POLICY,
     },
    ...
    };

    @@
    identifier ops.OPS;
    expression ops.POLICY;
    identifier fam;
    expression M;
    @@
    struct genl_family fam = {
            .ops = OPS,
            .maxattr = M,
    +       .policy = POLICY,
            ...
    };

This also gets rid of devlink_nl_cmd_region_read_dumpit() accessing
the cb->data as ops, which we want to change in a later genl patch.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 25 insertions, 3 deletions

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 4e62a4a8fa91..1b942a7caf26 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -650,16 +650,37 @@ static const struct genl_ops taskstats_ops[] = {
 	{
 		.cmd		= TASKSTATS_CMD_GET,
 		.doit		= taskstats_user_cmd,
-		.policy		= taskstats_cmd_get_policy,
-		.flags		= GENL_ADMIN_PERM,
+		/* policy enforced later */
+		.flags		= GENL_ADMIN_PERM | GENL_CMD_CAP_HASPOL,
 	},
 	{
 		.cmd		= CGROUPSTATS_CMD_GET,
 		.doit		= cgroupstats_user_cmd,
-		.policy		= cgroupstats_cmd_get_policy,
+		/* policy enforced later */
+		.flags		= GENL_CMD_CAP_HASPOL,
 	},
 };
 
+static int taskstats_pre_doit(const struct genl_ops *ops, struct sk_buff *skb,
+			      struct genl_info *info)
+{
+	const struct nla_policy *policy = NULL;
+
+	switch (ops->cmd) {
+	case TASKSTATS_CMD_GET:
+		policy = taskstats_cmd_get_policy;
+		break;
+	case CGROUPSTATS_CMD_GET:
+		policy = cgroupstats_cmd_get_policy;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return nlmsg_validate(info->nlhdr, GENL_HDRLEN, TASKSTATS_CMD_ATTR_MAX,
+			      policy, info->extack);
+}
+
 static struct genl_family family __ro_after_init = {
 	.name		= TASKSTATS_GENL_NAME,
 	.version	= TASKSTATS_GENL_VERSION,
@@ -667,6 +688,7 @@ static struct genl_family family __ro_after_init = {
 	.module		= THIS_MODULE,
 	.ops		= taskstats_ops,
 	.n_ops		= ARRAY_SIZE(taskstats_ops),
+	.pre_doit	= taskstats_pre_doit,
 };
 
 /* Needed early in initialization */