Commit f359b809 authored by Fernando Fernandez Mancera's avatar Fernando Fernandez Mancera Committed by Florian Westphal
Browse files

netfilter: nft_objref: validate objref and objrefmap expressions 



Referencing a synproxy stateful object from OUTPUT hook causes kernel
crash due to infinite recursive calls:

BUG: TASK stack guard page was hit at 000000008bda5b8c (stack is 000000003ab1c4a5..00000000494d8b12)
[...]
Call Trace:
 __find_rr_leaf+0x99/0x230
 fib6_table_lookup+0x13b/0x2d0
 ip6_pol_route+0xa4/0x400
 fib6_rule_lookup+0x156/0x240
 ip6_route_output_flags+0xc6/0x150
 __nf_ip6_route+0x23/0x50
 synproxy_send_tcp_ipv6+0x106/0x200
 synproxy_send_client_synack_ipv6+0x1aa/0x1f0
 nft_synproxy_do_eval+0x263/0x310
 nft_do_chain+0x5a8/0x5f0 [nf_tables
 nft_do_chain_inet+0x98/0x110
 nf_hook_slow+0x43/0xc0
 __ip6_local_out+0xf0/0x170
 ip6_local_out+0x17/0x70
 synproxy_send_tcp_ipv6+0x1a2/0x200
 synproxy_send_client_synack_ipv6+0x1aa/0x1f0
[...]

Implement objref and objrefmap expression validate functions.

Currently, only NFT_OBJECT_SYNPROXY object type requires validation.
This will also handle a jump to a chain using a synproxy object from the
OUTPUT hook.

Now when trying to reference a synproxy object in the OUTPUT hook, nft
will produce the following error:

synproxy_crash.nft: Error: Could not process rule: Operation not supported
  synproxy name mysynproxy
  ^^^^^^^^^^^^^^^^^^^^^^^^

Fixes: ee394f96 ("netfilter: nft_synproxy: add synproxy stateful object support")
Reported-by: default avatarGeorg Pfuetzenreuter <georg.pfuetzenreuter@suse.com>
Closes: https://bugzilla.suse.com/1250237


Signed-off-by: default avatarFernando Fernandez Mancera <fmancera@suse.de>
Reviewed-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
parent 2c95a756

net/netfilter/nft_objref.c

+39 −0
Original line number Diff line number Diff line
@@ -22,6 +22,35 @@ void nft_objref_eval(const struct nft_expr *expr, 
	obj->ops->eval(obj, regs, pkt);

}



static int nft_objref_validate_obj_type(const struct nft_ctx *ctx, u32 type)

{

	unsigned int hooks;



	switch (type) {

	case NFT_OBJECT_SYNPROXY:

		if (ctx->family != NFPROTO_IPV4 &&

		    ctx->family != NFPROTO_IPV6 &&

		    ctx->family != NFPROTO_INET)

			return -EOPNOTSUPP;



		hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD);



		return nft_chain_validate_hooks(ctx->chain, hooks);

	default:

		break;

	}



	return 0;

}



static int nft_objref_validate(const struct nft_ctx *ctx,

			       const struct nft_expr *expr)

{

	struct nft_object *obj = nft_objref_priv(expr);



	return nft_objref_validate_obj_type(ctx, obj->ops->type->type);

}



static int nft_objref_init(const struct nft_ctx *ctx,

			   const struct nft_expr *expr,

			   const struct nlattr * const tb[])
@@ -93,6 +122,7 @@ static const struct nft_expr_ops nft_objref_ops = { 
	.activate	= nft_objref_activate,

	.deactivate	= nft_objref_deactivate,

	.dump		= nft_objref_dump,

	.validate	= nft_objref_validate,

	.reduce		= NFT_REDUCE_READONLY,

};
@@ -197,6 +227,14 @@ static void nft_objref_map_destroy(const struct nft_ctx *ctx, 
	nf_tables_destroy_set(ctx, priv->set);

}



static int nft_objref_map_validate(const struct nft_ctx *ctx,

				   const struct nft_expr *expr)

{

	const struct nft_objref_map *priv = nft_expr_priv(expr);



	return nft_objref_validate_obj_type(ctx, priv->set->objtype);

}



static const struct nft_expr_ops nft_objref_map_ops = {

	.type		= &nft_objref_type,

	.size		= NFT_EXPR_SIZE(sizeof(struct nft_objref_map)),
@@ -206,6 +244,7 @@ static const struct nft_expr_ops nft_objref_map_ops = { 
	.deactivate	= nft_objref_map_deactivate,

	.destroy	= nft_objref_map_destroy,

	.dump		= nft_objref_map_dump,

	.validate	= nft_objref_map_validate,

	.reduce		= NFT_REDUCE_READONLY,

};