netfilter: nf_tables: must hold rcu read lock while iterating expression type list

nft shell tests trigger:
 WARNING: suspicious RCU usage
 net/netfilter/nf_tables_api.c:3125 RCU-list traversed in non-reader section!!
 1 lock held by nft/2068:
  #0: ffff888106c6f8c8 (&nft_net->commit_mutex){+.+.}-{4:4}, at: nf_tables_valid_genid+0x3c/0xf0

But the transaction mutex doesn't protect this list, the nfnl subsystem
mutex would, but we can't acquire it here without risk of ABBA
deadlocks.

Acquire the rcu read lock to avoid this issue.

v3: add a comment that explains the ->inner_ops check implies
expression is builtin and lack of a module owner reference is ok.

Fixes: 3a07327d10a0 ("netfilter: nft_inner: support for inner tunnel header matching")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 3b5154f2dd79833437c586490548aaa77dc4c147..de8e48a5c62d88707a9ae01c9dce8abe70e9fd4d 100644 (file)
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -3296,25 +3296,37 @@ int nft_expr_inner_parse(const struct nft_ctx *ctx, const struct nlattr *nla,
        if (!tb[NFTA_EXPR_DATA] || !tb[NFTA_EXPR_NAME])
                return -EINVAL;
 
+       rcu_read_lock();
+
        type = __nft_expr_type_get(ctx->family, tb[NFTA_EXPR_NAME]);
-       if (!type)
-               return -ENOENT;
+       if (!type) {
+               err = -ENOENT;
+               goto out_unlock;
+       }
 
-       if (!type->inner_ops)
-               return -EOPNOTSUPP;
+       if (!type->inner_ops) {
+               err = -EOPNOTSUPP;
+               goto out_unlock;
+       }
 
        err = nla_parse_nested_deprecated(info->tb, type->maxattr,
                                          tb[NFTA_EXPR_DATA],
                                          type->policy, NULL);
        if (err < 0)
-               goto err_nla_parse;
+               goto out_unlock;
 
        info->attr = nla;
        info->ops = type->inner_ops;
 
+       /* No module reference will be taken on type->owner.
+        * Presence of type->inner_ops implies that the expression
+        * is builtin, so it cannot go away.
+        */
+       rcu_read_unlock();
        return 0;
 
-err_nla_parse:
+out_unlock:
+       rcu_read_unlock();
        return err;
 }