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netfilter: nf_tables: prefer nft_chain_validate
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nft_chain_validate already performs loop detection because a cycle will
result in a call stack overflow (ctx->level >= NFT_JUMP_STACK_SIZE).

It also follows maps via ->validate callback in nft_lookup, so there
appears no reason to iterate the maps again.

nf_tables_check_loops() and all its helper functions can be removed.
This improves ruleset load time significantly, from 23s down to 12s.

This also fixes a crash bug. Old loop detection code can result in
unbounded recursion:

BUG: TASK stack guard page was hit at ....
Oops: stack guard page: 0000 [#1] PREEMPT SMP KASAN
CPU: 4 PID: 1539 Comm: nft Not tainted 6.10.0-rc5+ #1
[..]

with a suitable ruleset during validation of register stores.

I can't see any actual reason to attempt to check for this from
nft_validate_register_store(), at this point the transaction is still in
progress, so we don't have a full picture of the rule graph.

For nf-next it might make sense to either remove it or make this depend
on table->validate_state in case we could catch an error earlier
(for improved error reporting to userspace).

Fixes: 20a6934 ("netfilter: nf_tables: add netlink set API")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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@ummakynes
Florian Westphal authored and ummakynes committed Jul 11, 2024
1 parent 631a4b3 commit cff3bd0
Showing 1 changed file with 13 additions and 145 deletions.
158 changes: 13 additions & 145 deletions net/netfilter/nf_tables_api.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3823,6 +3823,15 @@ static void nf_tables_rule_release(const struct nft_ctx *ctx, struct nft_rule *r
nf_tables_rule_destroy(ctx, rule);
}

/** nft_chain_validate - loop detection and hook validation
*
* @ctx: context containing call depth and base chain
* @chain: chain to validate
*
* Walk through the rules of the given chain and chase all jumps/gotos
* and set lookups until either the jump limit is hit or all reachable
* chains have been validated.
*/
int nft_chain_validate(const struct nft_ctx *ctx, const struct nft_chain *chain)
{
struct nft_expr *expr, *last;
Expand All @@ -3844,6 +3853,9 @@ int nft_chain_validate(const struct nft_ctx *ctx, const struct nft_chain *chain)
if (!expr->ops->validate)
continue;

/* This may call nft_chain_validate() recursively,
* callers that do so must increment ctx->level.
*/
err = expr->ops->validate(ctx, expr, &data);
if (err < 0)
return err;
Expand Down Expand Up @@ -10809,150 +10821,6 @@ int nft_chain_validate_hooks(const struct nft_chain *chain,
}
EXPORT_SYMBOL_GPL(nft_chain_validate_hooks);

/*
* Loop detection - walk through the ruleset beginning at the destination chain
* of a new jump until either the source chain is reached (loop) or all
* reachable chains have been traversed.
*
* The loop check is performed whenever a new jump verdict is added to an
* expression or verdict map or a verdict map is bound to a new chain.
*/

static int nf_tables_check_loops(const struct nft_ctx *ctx,
const struct nft_chain *chain);

static int nft_check_loops(const struct nft_ctx *ctx,
const struct nft_set_ext *ext)
{
const struct nft_data *data;
int ret;

data = nft_set_ext_data(ext);
switch (data->verdict.code) {
case NFT_JUMP:
case NFT_GOTO:
ret = nf_tables_check_loops(ctx, data->verdict.chain);
break;
default:
ret = 0;
break;
}

return ret;
}

static int nf_tables_loop_check_setelem(const struct nft_ctx *ctx,
struct nft_set *set,
const struct nft_set_iter *iter,
struct nft_elem_priv *elem_priv)
{
const struct nft_set_ext *ext = nft_set_elem_ext(set, elem_priv);

if (!nft_set_elem_active(ext, iter->genmask))
return 0;

if (nft_set_ext_exists(ext, NFT_SET_EXT_FLAGS) &&
*nft_set_ext_flags(ext) & NFT_SET_ELEM_INTERVAL_END)
return 0;

return nft_check_loops(ctx, ext);
}

static int nft_set_catchall_loops(const struct nft_ctx *ctx,
struct nft_set *set)
{
u8 genmask = nft_genmask_next(ctx->net);
struct nft_set_elem_catchall *catchall;
struct nft_set_ext *ext;
int ret = 0;

list_for_each_entry_rcu(catchall, &set->catchall_list, list) {
ext = nft_set_elem_ext(set, catchall->elem);
if (!nft_set_elem_active(ext, genmask))
continue;

ret = nft_check_loops(ctx, ext);
if (ret < 0)
return ret;
}

return ret;
}

static int nf_tables_check_loops(const struct nft_ctx *ctx,
const struct nft_chain *chain)
{
const struct nft_rule *rule;
const struct nft_expr *expr, *last;
struct nft_set *set;
struct nft_set_binding *binding;
struct nft_set_iter iter;

if (ctx->chain == chain)
return -ELOOP;

if (fatal_signal_pending(current))
return -EINTR;

list_for_each_entry(rule, &chain->rules, list) {
nft_rule_for_each_expr(expr, last, rule) {
struct nft_immediate_expr *priv;
const struct nft_data *data;
int err;

if (strcmp(expr->ops->type->name, "immediate"))
continue;

priv = nft_expr_priv(expr);
if (priv->dreg != NFT_REG_VERDICT)
continue;

data = &priv->data;
switch (data->verdict.code) {
case NFT_JUMP:
case NFT_GOTO:
err = nf_tables_check_loops(ctx,
data->verdict.chain);
if (err < 0)
return err;
break;
default:
break;
}
}
}

list_for_each_entry(set, &ctx->table->sets, list) {
if (!nft_is_active_next(ctx->net, set))
continue;
if (!(set->flags & NFT_SET_MAP) ||
set->dtype != NFT_DATA_VERDICT)
continue;

list_for_each_entry(binding, &set->bindings, list) {
if (!(binding->flags & NFT_SET_MAP) ||
binding->chain != chain)
continue;

iter.genmask = nft_genmask_next(ctx->net);
iter.type = NFT_ITER_UPDATE;
iter.skip = 0;
iter.count = 0;
iter.err = 0;
iter.fn = nf_tables_loop_check_setelem;

set->ops->walk(ctx, set, &iter);
if (!iter.err)
iter.err = nft_set_catchall_loops(ctx, set);

if (iter.err < 0)
return iter.err;
}
}

return 0;
}

/**
* nft_parse_u32_check - fetch u32 attribute and check for maximum value
*
Expand Down Expand Up @@ -11065,7 +10933,7 @@ static int nft_validate_register_store(const struct nft_ctx *ctx,
if (data != NULL &&
(data->verdict.code == NFT_GOTO ||
data->verdict.code == NFT_JUMP)) {
err = nf_tables_check_loops(ctx, data->verdict.chain);
err = nft_chain_validate(ctx, data->verdict.chain);
if (err < 0)
return err;
}
Expand Down

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