[PATCH AUTOSEL 4.19 70/81] netfilter: nf_tables: use-after-free in dynamic operations

From: Pablo Neira Ayuso <pablo@netfilter.org>

[ Upstream commit 3f3a390dbd59d236f62cff8e8b20355ef7069e3d ]

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 <redacted>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <redacted>
---
 net/netfilter/nf_tables_api.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index f272f9538c44..ef7ff13a7b99 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c

@@ -2113,9 +2113,11 @@ static int nf_tables_newexpr(const struct nft_ctx *ctx,
 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,

-- 
2.20.1