[PATCH 3.16 199/305] netfilter: nf_tables: fix use-after-free when deleting compat expressions

[Ben Hutchings]

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Florian Westphal <fw@xxxxxxxxx>

commit 29e3880109e357fdc607b4393f8308cef6af9413 upstream.

nft_compat ops do not have static storage duration, unlike all other
expressions.

When nf_tables_expr_destroy() returns, expr->ops might have been
free'd already, so we need to store next address before calling
expression destructor.

For same reason, we can't deref match pointer after nft_xt_put().

This can be easily reproduced by adding msleep() before
nft_match_destroy() returns.

Fixes: 0ca743a55991 ("netfilter: nf_tables: add compatibility layer for x_tables")
Reported-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/netfilter/nf_tables_api.c | 5 +++--
 net/netfilter/nft_compat.c    | 3 ++-
 2 files changed, 5 insertions(+), 3 deletions(-)

--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -1682,7 +1682,7 @@ err:
 static void nf_tables_rule_destroy(const struct nft_ctx *ctx,
 				   struct nft_rule *rule)
 {
-	struct nft_expr *expr;
+	struct nft_expr *expr, *next;
 
 	/*
 	 * Careful: some expressions might not be initialized in case this
@@ -1690,8 +1690,9 @@ static void nf_tables_rule_destroy(const
 	 */
 	expr = nft_expr_first(rule);
 	while (expr != nft_expr_last(rule) && expr->ops) {
+		next = nft_expr_next(expr);
 		nf_tables_expr_destroy(ctx, expr);
-		expr = nft_expr_next(expr);
+		expr = next;
 	}
 	kfree(rule);
 }
--- a/net/netfilter/nft_compat.c
+++ b/net/netfilter/nft_compat.c
@@ -398,6 +398,7 @@ nft_match_destroy(const struct nft_ctx *
 {
 	struct xt_match *match = expr->ops->data;
 	void *info = nft_expr_priv(expr);
+	struct module *me = match->me;
 	struct xt_mtdtor_param par;
 
 	par.net = ctx->net;
@@ -407,7 +408,7 @@ nft_match_destroy(const struct nft_ctx *
 	if (par.match->destroy != NULL)
 		par.match->destroy(&par);
 
-	module_put(match->me);
+	module_put(me);
 }
 
 static int