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netfilter: nft_compat: use refcnt_t type for nft_xt reference count 

Using standard integer type was fine while all operations on it were
guarded by the nftnl subsys mutex.

This isn't true anymore:
1. transactions are guarded only by a pernet mutex, so concurrent
   rule manipulation in different netns is racy
2. the ->destroy hook runs from a work queue after the transaction
   mutex has been released already.

cpu0                           cpu1 (net 1)        cpu2 (net 2)
 kworker
    nft_compat->destroy        nft_compat->init    nft_compat->init
      if (--nft_xt->ref == 0)   nft_xt->ref++        nft_xt->ref++

Switch to refcount_t.  Doing this however only fixes a minor aspect,
nft_compat also performs linked-list operations in an unsafe way.

This is addressed in the next two patches.

Fixes: f102d66b33 ("netfilter: nf_tables: use dedicated mutex to guard transactions")
Fixes: 0935d55884 ("netfilter: nf_tables: asynchronous release")
Reported-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2019-01-14 14:28:48 +01:00 committed by Pablo Neira Ayuso
parent 88a8121dc1
commit 12c44aba66
1 changed files with 8 additions and 8 deletions
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16
net/netfilter/nft_compat.c
View File

@ -26,7 +26,7 @@
struct nft_xt { struct nft_xt {
struct list_head head; struct list_head head;
struct nft_expr_ops ops; struct nft_expr_ops ops;
unsigned int refcnt; refcount_t refcnt;
/* Unlike other expressions, ops doesn't have static storage duration. /* Unlike other expressions, ops doesn't have static storage duration.
* nft core assumes they do. We use kfree_rcu so that nft core can * nft core assumes they do. We use kfree_rcu so that nft core can
@ -45,7 +45,7 @@ struct nft_xt_match_priv {
static bool nft_xt_put(struct nft_xt *xt) static bool nft_xt_put(struct nft_xt *xt)
{ {
if (--xt->refcnt == 0) { if (refcount_dec_and_test(&xt->refcnt)) {
list_del(&xt->head); list_del(&xt->head);
kfree_rcu(xt, rcu_head); kfree_rcu(xt, rcu_head);
return true; return true;
@ -273,7 +273,7 @@ nft_target_init(const struct nft_ctx *ctx, const struct nft_expr *expr,
return -EINVAL; return -EINVAL;
nft_xt = container_of(expr->ops, struct nft_xt, ops); nft_xt = container_of(expr->ops, struct nft_xt, ops);
nft_xt->refcnt++; refcount_inc(&nft_xt->refcnt);
return 0; return 0;
} }
@ -486,7 +486,7 @@ __nft_match_init(const struct nft_ctx *ctx, const struct nft_expr *expr,
return ret; return ret;
nft_xt = container_of(expr->ops, struct nft_xt, ops); nft_xt = container_of(expr->ops, struct nft_xt, ops);
nft_xt->refcnt++; refcount_inc(&nft_xt->refcnt);
return 0; return 0;
} }
@ -789,7 +789,7 @@ nft_match_select_ops(const struct nft_ctx *ctx,
goto err; goto err;
} }
nft_match->refcnt = 0; refcount_set(&nft_match->refcnt, 0);
nft_match->ops.type = &nft_match_type; nft_match->ops.type = &nft_match_type;
nft_match->ops.eval = nft_match_eval; nft_match->ops.eval = nft_match_eval;
nft_match->ops.init = nft_match_init; nft_match->ops.init = nft_match_init;
@ -893,7 +893,7 @@ nft_target_select_ops(const struct nft_ctx *ctx,
goto err; goto err;
} }
nft_target->refcnt = 0; refcount_set(&nft_target->refcnt, 0);
nft_target->ops.type = &nft_target_type; nft_target->ops.type = &nft_target_type;
nft_target->ops.size = NFT_EXPR_SIZE(XT_ALIGN(target->targetsize)); nft_target->ops.size = NFT_EXPR_SIZE(XT_ALIGN(target->targetsize));
nft_target->ops.init = nft_target_init; nft_target->ops.init = nft_target_init;
@ -964,7 +964,7 @@ static void __exit nft_compat_module_exit(void)
list_for_each_entry_safe(xt, next, &nft_target_list, head) { list_for_each_entry_safe(xt, next, &nft_target_list, head) {
struct xt_target *target = xt->ops.data; struct xt_target *target = xt->ops.data;
if (WARN_ON_ONCE(xt->refcnt)) if (WARN_ON_ONCE(refcount_read(&xt->refcnt)))
continue; continue;
module_put(target->me); module_put(target->me);
kfree(xt); kfree(xt);
@ -973,7 +973,7 @@ static void __exit nft_compat_module_exit(void)
list_for_each_entry_safe(xt, next, &nft_match_list, head) { list_for_each_entry_safe(xt, next, &nft_match_list, head) {
struct xt_match *match = xt->ops.data; struct xt_match *match = xt->ops.data;
if (WARN_ON_ONCE(xt->refcnt)) if (WARN_ON_ONCE(refcount_read(&xt->refcnt)))
continue; continue;
module_put(match->me); module_put(match->me);
kfree(xt); kfree(xt);