netfilter: nf_tables: use-after-free in dynamic operations

Smatch reports:

       net/netfilter/nf_tables_api.c:2167 nf_tables_expr_destroy()
        error: dereferencing freed memory 'expr->ops'

net/netfilter/nf_tables_api.c
    2162 static void nf_tables_expr_destroy(const struct nft_ctx *ctx,
    2163                                   struct nft_expr *expr)
    2164 {
    2165        if (expr->ops->destroy)
    2166                expr->ops->destroy(ctx, expr);
                                                ^^^^
--> 2167        module_put(expr->ops->type->owner);
                           ^^^^^^^^^
    2168 }

Smatch says there are three functions which free expr->ops.

Fixes: b8e204006340 ("netfilter: nft_compat: use .release_ops and remove list of extension")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
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 ca09ef037ca57a66ed79f93264ad8eca00d4521a..9d8f51dfc59363266bb81371d0f9f99241c8d1bb 100644 (file)
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -2162,9 +2162,11 @@ err1:
 static void nf_tables_expr_destroy(const struct nft_ctx *ctx,
                                   struct nft_expr *expr)
 {
+       const struct nft_expr_type *type = expr->ops->type;
+
        if (expr->ops->destroy)
                expr->ops->destroy(ctx, expr);
-       module_put(expr->ops->type->owner);
+       module_put(type->owner);
 }
 
 struct nft_expr *nft_expr_init(const struct nft_ctx *ctx,