* [PATCH] netfilter: nfnetlink: Remove VLA usage
@ 2018-05-30 0:35 Kees Cook
2018-05-30 8:19 ` Florian Westphal
2018-05-30 9:52 ` Pablo Neira Ayuso
0 siblings, 2 replies; 4+ messages in thread
From: Kees Cook @ 2018-05-30 0:35 UTC (permalink / raw)
To: Pablo Neira Ayuso
Cc: Jozsef Kadlecsik, Florian Westphal, David S. Miller,
netfilter-devel, coreteam, netdev, linux-kernel
In the quest to remove all stack VLA usage from the kernel[1], this
allocates the maximum size expected for all possible attrs and adds
a sanity-check to make sure nothing gets out of sync.
[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
Signed-off-by: Kees Cook <keescook@chromium.org>
---
net/netfilter/nfnetlink.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index 03ead8a9e90c..0cb395f9627e 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -28,6 +28,7 @@
#include <net/netlink.h>
#include <linux/netfilter/nfnetlink.h>
+#include <linux/netfilter/nf_tables.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
@@ -37,6 +38,11 @@ MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_NETFILTER);
rcu_dereference_protected(table[(id)].subsys, \
lockdep_nfnl_is_held((id)))
+#define NFTA_MAX_ATTR max(max(max(NFTA_CHAIN_MAX, NFTA_FLOWTABLE_MAX),\
+ max(NFTA_OBJ_MAX, NFTA_RULE_MAX)), \
+ max(NFTA_TABLE_MAX, \
+ max(NFTA_SET_ELEM_LIST_MAX, NFTA_SET_MAX)))
+
static struct {
struct mutex mutex;
const struct nfnetlink_subsystem __rcu *subsys;
@@ -185,11 +191,17 @@ static int nfnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
{
int min_len = nlmsg_total_size(sizeof(struct nfgenmsg));
u8 cb_id = NFNL_MSG_TYPE(nlh->nlmsg_type);
- struct nlattr *cda[ss->cb[cb_id].attr_count + 1];
+ struct nlattr *cda[NFTA_MAX_ATTR + 1];
struct nlattr *attr = (void *)nlh + min_len;
int attrlen = nlh->nlmsg_len - min_len;
__u8 subsys_id = NFNL_SUBSYS_ID(type);
+ /* Sanity-check NFTA_MAX_ATTR */
+ if (ss->cb[cb_id].attr_count > NFTA_MAX_ATTR) {
+ rcu_read_unlock();
+ return -ENOMEM;
+ }
+
err = nla_parse(cda, ss->cb[cb_id].attr_count, attr, attrlen,
ss->cb[cb_id].policy, extack);
if (err < 0) {
@@ -379,10 +391,16 @@ static void nfnetlink_rcv_batch(struct sk_buff *skb, struct nlmsghdr *nlh,
{
int min_len = nlmsg_total_size(sizeof(struct nfgenmsg));
u8 cb_id = NFNL_MSG_TYPE(nlh->nlmsg_type);
- struct nlattr *cda[ss->cb[cb_id].attr_count + 1];
+ struct nlattr *cda[NFTA_MAX_ATTR + 1];
struct nlattr *attr = (void *)nlh + min_len;
int attrlen = nlh->nlmsg_len - min_len;
+ /* Sanity-check NFTA_MAX_ATTR */
+ if (ss->cb[cb_id].attr_count > NFTA_MAX_ATTR) {
+ err = -ENOMEM;
+ goto ack;
+ }
+
err = nla_parse(cda, ss->cb[cb_id].attr_count, attr,
attrlen, ss->cb[cb_id].policy, NULL);
if (err < 0)
--
2.17.0
--
Kees Cook
Pixel Security
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] netfilter: nfnetlink: Remove VLA usage
2018-05-30 0:35 [PATCH] netfilter: nfnetlink: Remove VLA usage Kees Cook
@ 2018-05-30 8:19 ` Florian Westphal
2018-05-30 9:52 ` Pablo Neira Ayuso
1 sibling, 0 replies; 4+ messages in thread
From: Florian Westphal @ 2018-05-30 8:19 UTC (permalink / raw)
To: Kees Cook
Cc: Pablo Neira Ayuso, Jozsef Kadlecsik, Florian Westphal,
David S. Miller, netfilter-devel, coreteam, netdev, linux-kernel
Kees Cook <keescook@chromium.org> wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> allocates the maximum size expected for all possible attrs and adds
> a sanity-check to make sure nothing gets out of sync.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> net/netfilter/nfnetlink.c | 22 ++++++++++++++++++++--
> 1 file changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
> index 03ead8a9e90c..0cb395f9627e 100644
> --- a/net/netfilter/nfnetlink.c
> +++ b/net/netfilter/nfnetlink.c
> @@ -28,6 +28,7 @@
>
> #include <net/netlink.h>
> #include <linux/netfilter/nfnetlink.h>
> +#include <linux/netfilter/nf_tables.h>
>
> const struct nfnetlink_subsystem __rcu *subsys;
> @@ -185,11 +191,17 @@ static int nfnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
> {
> int min_len = nlmsg_total_size(sizeof(struct nfgenmsg));
> u8 cb_id = NFNL_MSG_TYPE(nlh->nlmsg_type);
> - struct nlattr *cda[ss->cb[cb_id].attr_count + 1];
> + struct nlattr *cda[NFTA_MAX_ATTR + 1];
> struct nlattr *attr = (void *)nlh + min_len;
> int attrlen = nlh->nlmsg_len - min_len;
> __u8 subsys_id = NFNL_SUBSYS_ID(type);
>
> + /* Sanity-check NFTA_MAX_ATTR */
> + if (ss->cb[cb_id].attr_count > NFTA_MAX_ATTR) {
> + rcu_read_unlock();
> + return -ENOMEM;
> + }
Would you mind also adding check to nfnetlink_subsys_register, plus WARN()?
That way we'll see that NFTA_MAX_ATTR isn't large enough by virtue
of registration rather than actual use.
Other than that this looks fine to me.
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] netfilter: nfnetlink: Remove VLA usage
2018-05-30 0:35 [PATCH] netfilter: nfnetlink: Remove VLA usage Kees Cook
2018-05-30 8:19 ` Florian Westphal
@ 2018-05-30 9:52 ` Pablo Neira Ayuso
2018-05-30 19:08 ` Kees Cook
1 sibling, 1 reply; 4+ messages in thread
From: Pablo Neira Ayuso @ 2018-05-30 9:52 UTC (permalink / raw)
To: Kees Cook
Cc: Jozsef Kadlecsik, Florian Westphal, David S. Miller,
netfilter-devel, coreteam, netdev, linux-kernel
On Tue, May 29, 2018 at 05:35:25PM -0700, Kees Cook wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> allocates the maximum size expected for all possible attrs and adds
> a sanity-check to make sure nothing gets out of sync.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> net/netfilter/nfnetlink.c | 22 ++++++++++++++++++++--
> 1 file changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
> index 03ead8a9e90c..0cb395f9627e 100644
> --- a/net/netfilter/nfnetlink.c
> +++ b/net/netfilter/nfnetlink.c
> @@ -28,6 +28,7 @@
>
> #include <net/netlink.h>
> #include <linux/netfilter/nfnetlink.h>
> +#include <linux/netfilter/nf_tables.h>
>
> MODULE_LICENSE("GPL");
> MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
> @@ -37,6 +38,11 @@ MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_NETFILTER);
> rcu_dereference_protected(table[(id)].subsys, \
> lockdep_nfnl_is_held((id)))
>
> +#define NFTA_MAX_ATTR max(max(max(NFTA_CHAIN_MAX, NFTA_FLOWTABLE_MAX),\
> + max(NFTA_OBJ_MAX, NFTA_RULE_MAX)), \
> + max(NFTA_TABLE_MAX, \
> + max(NFTA_SET_ELEM_LIST_MAX, NFTA_SET_MAX)))
This is very specific of nftables, there are other nf subsystems using
nfnetlink that may go over this maximum attribute value (grep from
"struct nfnetlink_subsystem").
To remove the VLA, I think we need an artificial maximum attribute
that reasonably large enough.
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] netfilter: nfnetlink: Remove VLA usage
2018-05-30 9:52 ` Pablo Neira Ayuso
@ 2018-05-30 19:08 ` Kees Cook
0 siblings, 0 replies; 4+ messages in thread
From: Kees Cook @ 2018-05-30 19:08 UTC (permalink / raw)
To: Pablo Neira Ayuso
Cc: Jozsef Kadlecsik, Florian Westphal, David S. Miller,
netfilter-devel, coreteam, Network Development, LKML
On Wed, May 30, 2018 at 2:52 AM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> On Tue, May 29, 2018 at 05:35:25PM -0700, Kees Cook wrote:
>> In the quest to remove all stack VLA usage from the kernel[1], this
>> allocates the maximum size expected for all possible attrs and adds
>> a sanity-check to make sure nothing gets out of sync.
>>
>> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>>
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>> ---
>> net/netfilter/nfnetlink.c | 22 ++++++++++++++++++++--
>> 1 file changed, 20 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
>> index 03ead8a9e90c..0cb395f9627e 100644
>> --- a/net/netfilter/nfnetlink.c
>> +++ b/net/netfilter/nfnetlink.c
>> @@ -28,6 +28,7 @@
>>
>> #include <net/netlink.h>
>> #include <linux/netfilter/nfnetlink.h>
>> +#include <linux/netfilter/nf_tables.h>
>>
>> MODULE_LICENSE("GPL");
>> MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
>> @@ -37,6 +38,11 @@ MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_NETFILTER);
>> rcu_dereference_protected(table[(id)].subsys, \
>> lockdep_nfnl_is_held((id)))
>>
>> +#define NFTA_MAX_ATTR max(max(max(NFTA_CHAIN_MAX, NFTA_FLOWTABLE_MAX),\
>> + max(NFTA_OBJ_MAX, NFTA_RULE_MAX)), \
>> + max(NFTA_TABLE_MAX, \
>> + max(NFTA_SET_ELEM_LIST_MAX, NFTA_SET_MAX)))
>
> This is very specific of nftables, there are other nf subsystems using
> nfnetlink that may go over this maximum attribute value (grep from
> "struct nfnetlink_subsystem").
Oops, yes. I see that now.
> To remove the VLA, I think we need an artificial maximum attribute
> that reasonably large enough.
git grep insanity:
$ for i in $(git grep -A10 'static .*struct nfnetlink_subsystem' | \
grep '\.cb\b' | awk '{print $NF}' | cut -d, -f1)
do git grep -A100 'static .*'"$i\b"; done | \
grep '\.attr_count\b' | awk -F= '{print $NF}' | \
sed -e 's/ //g' | cut -d, -f1 | sort -u
and manual counting gets me:
CTA_EXPECT_MAX 12
CTA_MAX 25
CTA_TIMEOUT_MAX 6
IPSET_ATTR_CMD_MAX 11
NFACCT_MAX 9
NFCTH_MAX 7
NFQA_CFG_MAX 6
NFQA_MAX 21
NFTA_CHAIN_MAX 10
NFTA_COMPAT_MAX 4
NFTA_OBJ_MAX 8
NFTA_RULE_MAX 10
NFTA_SET_ELEM_LIST_MAX 5
NFTA_SET_MAX 17
NFTA_TABLE_MAX 6
NFULA_CFG_MAX 7
NFULA_MAX 20
OSF_ATTR_MAX 2
How about 32?
As Florian suggested, I'll add the check in
nfnetlink_subsys_register() with a WARN().
-Kees
--
Kees Cook
Pixel Security
^ permalink raw reply [flat|nested] 4+ messages in thread
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2018-05-30 0:35 [PATCH] netfilter: nfnetlink: Remove VLA usage Kees Cook
2018-05-30 8:19 ` Florian Westphal
2018-05-30 9:52 ` Pablo Neira Ayuso
2018-05-30 19:08 ` Kees Cook
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