act_ife: fix a potential deadlock

use_all_metadata() acquires read_lock(&ife_mod_lock), then calls
add_metainfo() which calls find_ife_oplist() which acquires the same
lock again. Deadlock!

Introduce __add_metainfo() which accepts struct tcf_meta_ops *ops
as an additional parameter and let its callers to decide how
to find it. For use_all_metadata(), it already has ops, no
need to find it again, just call __add_metainfo() directly.

And, as ife_mod_lock is only needed for find_ife_oplist(),
this means we can make non-atomic allocation for populate_metalist()
now.

Fixes: 817e9f2c5c ("act_ife: acquire ife_mod_lock before reading ifeoplist")
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_ife.c

@@ -296,22 +296,16 @@ static int load_metaops_and_vet(u32 metaid, void *val, int len, bool rtnl_held)
 
 /* called when adding new meta information
 */
-static int add_metainfo(struct tcf_ife_info *ife, u32 metaid, void *metaval,
-			int len, bool atomic, bool exists)
+static int __add_metainfo(const struct tcf_meta_ops *ops,
+			  struct tcf_ife_info *ife, u32 metaid, void *metaval,
+			  int len, bool atomic, bool exists)
 {
 	struct tcf_meta_info *mi = NULL;
-	struct tcf_meta_ops *ops = find_ife_oplist(metaid);
 	int ret = 0;
 
-	if (!ops)
-		return -ENOENT;
-
 	mi = kzalloc(sizeof(*mi), atomic ? GFP_ATOMIC : GFP_KERNEL);
-	if (!mi) {
-		/*put back what find_ife_oplist took */
-		module_put(ops->owner);
+	if (!mi)
 		return -ENOMEM;
-	}
 
 	mi->metaid = metaid;
 	mi->ops = ops;
@@ -319,7 +313,6 @@ static int add_metainfo(struct tcf_ife_info *ife, u32 metaid, void *metaval,
 		ret = ops->alloc(mi, metaval, atomic ? GFP_ATOMIC : GFP_KERNEL);
 		if (ret != 0) {
 			kfree(mi);
-			module_put(ops->owner);
 			return ret;
 		}
 	}
@@ -333,6 +326,21 @@ static int add_metainfo(struct tcf_ife_info *ife, u32 metaid, void *metaval,
 	return ret;
 }
 
+static int add_metainfo(struct tcf_ife_info *ife, u32 metaid, void *metaval,
+			int len, bool exists)
+{
+	const struct tcf_meta_ops *ops = find_ife_oplist(metaid);
+	int ret;
+
+	if (!ops)
+		return -ENOENT;
+	ret = __add_metainfo(ops, ife, metaid, metaval, len, false, exists);
+	if (ret)
+		/*put back what find_ife_oplist took */
+		module_put(ops->owner);
+	return ret;
+}
+
 static int use_all_metadata(struct tcf_ife_info *ife, bool exists)
 {
 	struct tcf_meta_ops *o;
@@ -341,7 +349,7 @@ static int use_all_metadata(struct tcf_ife_info *ife, bool exists)
 
 	read_lock(&ife_mod_lock);
 	list_for_each_entry(o, &ifeoplist, list) {
-		rc = add_metainfo(ife, o->metaid, NULL, 0, true, exists);
+		rc = __add_metainfo(o, ife, o->metaid, NULL, 0, true, exists);
 		if (rc == 0)
 			installed += 1;
 	}
@@ -435,7 +443,7 @@ static int populate_metalist(struct tcf_ife_info *ife, struct nlattr **tb,
 			if (rc != 0)
 				return rc;
 
-			rc = add_metainfo(ife, i, val, len, false, exists);
+			rc = add_metainfo(ife, i, val, len, exists);
 			if (rc)
 				return rc;
 		}