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author | Florian Westphal <fw@strlen.de> | 2023-04-11 17:29:45 +0300 |
---|---|---|
committer | Pablo Neira Ayuso <pablo@netfilter.org> | 2023-04-22 02:39:40 +0300 |
commit | e38fbfa972eb0944ce4387caf23d166c1df4b114 (patch) | |
tree | 3e0ac83a53a450354a97ca28da65daca9ac8bbdc /net/netfilter/nf_tables_api.c | |
parent | ca288965801572fe41386560d4e6c5cc0e5cc56d (diff) | |
download | linux-e38fbfa972eb0944ce4387caf23d166c1df4b114.tar.xz |
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 <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Diffstat (limited to 'net/netfilter/nf_tables_api.c')
-rw-r--r-- | net/netfilter/nf_tables_api.c | 55 |
1 files 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; + + BUILD_BUG_ON(offsetof(struct nft_rule_dp_last, end) != 0); - prule = (struct nft_rule_dp *)ptr; - prule->is_last = 1; + 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) |