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netfilter: nft_compat: fix crash when related match/target module is …
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…removed

We "cache" the loaded match/target modules and reuse them, but when the
modules are removed, we still point to them. Then we may end up with
invalid memory references when using iptables-compat to add rules later.

Input the following commands will reproduce the kernel crash:
  # iptables-compat -A INPUT -j LOG
  # iptables-compat -D INPUT -j LOG
  # rmmod xt_LOG
  # iptables-compat -A INPUT -j LOG
  BUG: unable to handle kernel paging request at ffffffffa05a9010
  IP: [<ffffffff813f783e>] strcmp+0xe/0x30
  Call Trace:
  [<ffffffffa05acc43>] nft_target_select_ops+0x83/0x1f0 [nft_compat]
  [<ffffffffa058a177>] nf_tables_expr_parse+0x147/0x1f0 [nf_tables]
  [<ffffffffa058e541>] nf_tables_newrule+0x301/0x810 [nf_tables]
  [<ffffffff8141ca00>] ? nla_parse+0x20/0x100
  [<ffffffffa057fa8f>] nfnetlink_rcv+0x33f/0x53d [nfnetlink]
  [<ffffffffa057f94b>] ? nfnetlink_rcv+0x1fb/0x53d [nfnetlink]
  [<ffffffff817116b8>] netlink_unicast+0x178/0x220
  [<ffffffff81711a5b>] netlink_sendmsg+0x2fb/0x3a0
  [<ffffffff816b7fc8>] sock_sendmsg+0x38/0x50
  [<ffffffff816b8a7e>] ___sys_sendmsg+0x28e/0x2a0
  [<ffffffff816bcb7e>] ? release_sock+0x1e/0xb0
  [<ffffffff81804ac5>] ? _raw_spin_unlock_bh+0x35/0x40
  [<ffffffff816bcbe2>] ? release_sock+0x82/0xb0
  [<ffffffff816b93d4>] __sys_sendmsg+0x54/0x90
  [<ffffffff816b9422>] SyS_sendmsg+0x12/0x20
  [<ffffffff81805172>] entry_SYSCALL_64_fastpath+0x1a/0xa9

So when nobody use the related match/target module, there's no need to
"cache" it. And nft_[match|target]_release are useless anymore, remove
them.

Signed-off-by: Liping Zhang <liping.zhang@spreadtrum.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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Liping Zhang authored and Pablo Neira Ayuso committed Jul 23, 2016
1 parent 2bf4fad commit 4b512e1
Showing 1 changed file with 20 additions and 23 deletions.
43 changes: 20 additions & 23 deletions net/netfilter/nft_compat.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,20 @@
#include <linux/netfilter_arp/arp_tables.h>
#include <net/netfilter/nf_tables.h>

struct nft_xt {
struct list_head head;
struct nft_expr_ops ops;
unsigned int refcnt;
};

static void nft_xt_put(struct nft_xt *xt)
{
if (--xt->refcnt == 0) {
list_del(&xt->head);
kfree(xt);
}
}

static int nft_compat_chain_validate_dependency(const char *tablename,
const struct nft_chain *chain)
{
Expand Down Expand Up @@ -260,6 +274,7 @@ nft_target_destroy(const struct nft_ctx *ctx, const struct nft_expr *expr)
if (par.target->destroy != NULL)
par.target->destroy(&par);

nft_xt_put(container_of(expr->ops, struct nft_xt, ops));
module_put(target->me);
}

Expand Down Expand Up @@ -442,6 +457,7 @@ nft_match_destroy(const struct nft_ctx *ctx, const struct nft_expr *expr)
if (par.match->destroy != NULL)
par.match->destroy(&par);

nft_xt_put(container_of(expr->ops, struct nft_xt, ops));
module_put(match->me);
}

Expand Down Expand Up @@ -612,11 +628,6 @@ static const struct nfnetlink_subsystem nfnl_compat_subsys = {

static LIST_HEAD(nft_match_list);

struct nft_xt {
struct list_head head;
struct nft_expr_ops ops;
};

static struct nft_expr_type nft_match_type;

static bool nft_match_cmp(const struct xt_match *match,
Expand Down Expand Up @@ -653,6 +664,7 @@ nft_match_select_ops(const struct nft_ctx *ctx,
if (!try_module_get(match->me))
return ERR_PTR(-ENOENT);

nft_match->refcnt++;
return &nft_match->ops;
}
}
Expand All @@ -673,6 +685,7 @@ nft_match_select_ops(const struct nft_ctx *ctx,
goto err;
}

nft_match->refcnt = 1;
nft_match->ops.type = &nft_match_type;
nft_match->ops.size = NFT_EXPR_SIZE(XT_ALIGN(match->matchsize));
nft_match->ops.eval = nft_match_eval;
Expand All @@ -690,14 +703,6 @@ nft_match_select_ops(const struct nft_ctx *ctx,
return ERR_PTR(err);
}

static void nft_match_release(void)
{
struct nft_xt *nft_match, *tmp;

list_for_each_entry_safe(nft_match, tmp, &nft_match_list, head)
kfree(nft_match);
}

static struct nft_expr_type nft_match_type __read_mostly = {
.name = "match",
.select_ops = nft_match_select_ops,
Expand Down Expand Up @@ -744,6 +749,7 @@ nft_target_select_ops(const struct nft_ctx *ctx,
if (!try_module_get(target->me))
return ERR_PTR(-ENOENT);

nft_target->refcnt++;
return &nft_target->ops;
}
}
Expand All @@ -764,6 +770,7 @@ nft_target_select_ops(const struct nft_ctx *ctx,
goto err;
}

nft_target->refcnt = 1;
nft_target->ops.type = &nft_target_type;
nft_target->ops.size = NFT_EXPR_SIZE(XT_ALIGN(target->targetsize));
nft_target->ops.init = nft_target_init;
Expand All @@ -785,14 +792,6 @@ nft_target_select_ops(const struct nft_ctx *ctx,
return ERR_PTR(err);
}

static void nft_target_release(void)
{
struct nft_xt *nft_target, *tmp;

list_for_each_entry_safe(nft_target, tmp, &nft_target_list, head)
kfree(nft_target);
}

static struct nft_expr_type nft_target_type __read_mostly = {
.name = "target",
.select_ops = nft_target_select_ops,
Expand Down Expand Up @@ -835,8 +834,6 @@ static void __exit nft_compat_module_exit(void)
nfnetlink_subsys_unregister(&nfnl_compat_subsys);
nft_unregister_expr(&nft_target_type);
nft_unregister_expr(&nft_match_type);
nft_match_release();
nft_target_release();
}

MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_NFT_COMPAT);
Expand Down

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