From e38fbfa972eb0944ce4387caf23d166c1df4b114 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Tue, 11 Apr 2023 16:29:45 +0200 Subject: [PATCH] netfilter: nf_tables: merge nft_rules_old structure and end of ruleblob marker In order to free the rules in a chain via call_rcu, the rule array used to stash a rcu_head and space for a pointer at the end of the rule array. When the current nft_rule_dp blob format got added in 2c865a8a28a1 ("netfilter: nf_tables: add rule blob layout"), this results in a double-trailer: size (unsigned long) struct nft_rule_dp struct nft_expr ... struct nft_rule_dp struct nft_expr ... struct nft_rule_dp (is_last=1) // Trailer The trailer, struct nft_rule_dp (is_last=1), is not accounted for in size, so it can be located via start_addr + size. Because the rcu_head is stored after 'start+size' as well this means the is_last trailer is *aliased* to the rcu_head (struct nft_rules_old). This is harmless, because at this time the nft_do_chain function never evaluates/accesses the trailer, it only checks the address boundary: for (; rule < last_rule; rule = nft_rule_next(rule)) { ... But this way the last_rule address has to be stashed in the jump structure to restore it after returning from a chain. nft_do_chain stack usage has become way too big, so put it on a diet. Without this patch is impossible to use for (; !rule->is_last; rule = nft_rule_next(rule)) { ... because on free, the needed update of the rcu_head will clobber the nft_rule_dp is_last bit. Furthermore, also stash the chain pointer in the trailer, this allows to recover the original chain structure from nf_tables_trace infra without a need to place them in the jump struct. After this patch it is trivial to diet the jump stack structure, done in the next two patches. Signed-off-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_tables_api.c | 55 +++++++++++++++++------------------ 1 file changed, 27 insertions(+), 28 deletions(-) diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c index e48ab8dfb541..79848a27e640 100644 --- a/net/netfilter/nf_tables_api.c +++ b/net/netfilter/nf_tables_api.c @@ -2110,38 +2110,41 @@ static void nft_chain_release_hook(struct nft_chain_hook *hook) module_put(hook->type->owner); } -struct nft_rules_old { +struct nft_rule_dp_last { + struct nft_rule_dp end; /* end of nft_rule_blob marker */ struct rcu_head h; struct nft_rule_blob *blob; + const struct nft_chain *chain; /* for tracing */ }; -static void nft_last_rule(struct nft_rule_blob *blob, const void *ptr) +static void nft_last_rule(const struct nft_chain *chain, const void *ptr) { - struct nft_rule_dp *prule; + struct nft_rule_dp_last *lrule; - prule = (struct nft_rule_dp *)ptr; - prule->is_last = 1; + BUILD_BUG_ON(offsetof(struct nft_rule_dp_last, end) != 0); + + lrule = (struct nft_rule_dp_last *)ptr; + lrule->end.is_last = 1; + lrule->chain = chain; /* blob size does not include the trailer rule */ } -static struct nft_rule_blob *nf_tables_chain_alloc_rules(unsigned int size) +static struct nft_rule_blob *nf_tables_chain_alloc_rules(const struct nft_chain *chain, + unsigned int size) { struct nft_rule_blob *blob; - /* size must include room for the last rule */ - if (size < offsetof(struct nft_rule_dp, data)) - return NULL; - - size += sizeof(struct nft_rule_blob) + sizeof(struct nft_rules_old); if (size > INT_MAX) return NULL; + size += sizeof(struct nft_rule_blob) + sizeof(struct nft_rule_dp_last); + blob = kvmalloc(size, GFP_KERNEL_ACCOUNT); if (!blob) return NULL; blob->size = 0; - nft_last_rule(blob, blob->data); + nft_last_rule(chain, blob->data); return blob; } @@ -2220,7 +2223,6 @@ static int nf_tables_addchain(struct nft_ctx *ctx, u8 family, u8 genmask, struct nft_rule_blob *blob; struct nft_trans *trans; struct nft_chain *chain; - unsigned int data_size; int err; if (table->use == UINT_MAX) @@ -2308,8 +2310,7 @@ static int nf_tables_addchain(struct nft_ctx *ctx, u8 family, u8 genmask, chain->udlen = nla_len(nla[NFTA_CHAIN_USERDATA]); } - data_size = offsetof(struct nft_rule_dp, data); /* last rule */ - blob = nf_tables_chain_alloc_rules(data_size); + blob = nf_tables_chain_alloc_rules(chain, 0); if (!blob) { err = -ENOMEM; goto err_destroy_chain; @@ -8817,9 +8818,8 @@ static int nf_tables_commit_chain_prepare(struct net *net, struct nft_chain *cha return -ENOMEM; } } - data_size += offsetof(struct nft_rule_dp, data); /* last rule */ - chain->blob_next = nf_tables_chain_alloc_rules(data_size); + chain->blob_next = nf_tables_chain_alloc_rules(chain, data_size); if (!chain->blob_next) return -ENOMEM; @@ -8864,12 +8864,11 @@ static int nf_tables_commit_chain_prepare(struct net *net, struct nft_chain *cha chain->blob_next->size += (unsigned long)(data - (void *)prule); } - prule = (struct nft_rule_dp *)data; - data += offsetof(struct nft_rule_dp, data); if (WARN_ON_ONCE(data > data_boundary)) return -ENOMEM; - nft_last_rule(chain->blob_next, prule); + prule = (struct nft_rule_dp *)data; + nft_last_rule(chain, prule); return 0; } @@ -8890,22 +8889,22 @@ static void nf_tables_commit_chain_prepare_cancel(struct net *net) } } -static void __nf_tables_commit_chain_free_rules_old(struct rcu_head *h) +static void __nf_tables_commit_chain_free_rules(struct rcu_head *h) { - struct nft_rules_old *o = container_of(h, struct nft_rules_old, h); + struct nft_rule_dp_last *l = container_of(h, struct nft_rule_dp_last, h); - kvfree(o->blob); + kvfree(l->blob); } static void nf_tables_commit_chain_free_rules_old(struct nft_rule_blob *blob) { - struct nft_rules_old *old; + struct nft_rule_dp_last *last; - /* rcu_head is after end marker */ - old = (void *)blob + sizeof(*blob) + blob->size; - old->blob = blob; + /* last rule trailer is after end marker */ + last = (void *)blob + sizeof(*blob) + blob->size; + last->blob = blob; - call_rcu(&old->h, __nf_tables_commit_chain_free_rules_old); + call_rcu(&last->h, __nf_tables_commit_chain_free_rules); } static void nf_tables_commit_chain(struct net *net, struct nft_chain *chain)