Re: [netfilter-core] [PATCH v2] netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv

[Pablo Neira Ayuso]

On Thu, Jun 29, 2017 at 06:22:40PM +0200, Pablo Neira Ayuso wrote:
> On Tue, Jun 27, 2017 at 07:05:27PM +0200, Pablo Neira Ayuso wrote:
> > On Tue, Jun 27, 2017 at 05:58:25PM +0200, Pablo Neira Ayuso wrote:
> > > On Wed, Jun 07, 2017 at 03:50:38PM +0200, Mateusz Jurczyk wrote:
> > > > Verify that the length of the socket buffer is sufficient to cover the
> > > > nlmsghdr structure before accessing the nlh->nlmsg_len field for further
> > > > input sanitization. If the client only supplies 1-3 bytes of data in
> > > > sk_buff, then nlh->nlmsg_len remains partially uninitialized and
> > > > contains leftover memory from the corresponding kernel allocation.
> > > > Operating on such data may result in indeterminate evaluation of the
> > > > nlmsg_len < NLMSG_HDRLEN expression.
> > > > 
> > > > The bug was discovered by a runtime instrumentation designed to detect
> > > > use of uninitialized memory in the kernel. The patch prevents this and
> > > > other similar tools (e.g. KMSAN) from flagging this behavior in the 
> > > > future.
> > > 
> > > Applied, thanks.
> > 
> > Wait, I keeping this back after closer look.
> > 
> > I think we have to remove this:
> > 
> > if (nlh->nlmsg_len < NLMSG_HDRLEN || <---
> > skb->len < NLMSG_HDRLEN + sizeof(struct nfgenmsg))
> > return;
> > 
> > in nfnetlink_rcv_skb_batch()
> > 
> > now that we make this unfront check from nfnetlink_rcv().
> 
> BTW, I can just mangle your patch here to delete such line to speed up
> things. See the mangled patch that is attached to this email.

OK, I have applied this to the nf tree.

Thanks!

Re: [PATCH v2] netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv

[Mateusz Jurczyk]

On Thu, Jun 29, 2017 at 6:22 PM, Pablo Neira Ayuso  wrote:
> On Tue, Jun 27, 2017 at 07:05:27PM +0200, Pablo Neira Ayuso wrote:
>> On Tue, Jun 27, 2017 at 05:58:25PM +0200, Pablo Neira Ayuso wrote:
>> > On Wed, Jun 07, 2017 at 03:50:38PM +0200, Mateusz Jurczyk wrote:
>> > > Verify that the length of the socket buffer is sufficient to cover the
>> > > nlmsghdr structure before accessing the nlh->nlmsg_len field for further
>> > > input sanitization. If the client only supplies 1-3 bytes of data in
>> > > sk_buff, then nlh->nlmsg_len remains partially uninitialized and
>> > > contains leftover memory from the corresponding kernel allocation.
>> > > Operating on such data may result in indeterminate evaluation of the
>> > > nlmsg_len < NLMSG_HDRLEN expression.
>> > >
>> > > The bug was discovered by a runtime instrumentation designed to detect
>> > > use of uninitialized memory in the kernel. The patch prevents this and
>> > > other similar tools (e.g. KMSAN) from flagging this behavior in the 
>> > > future.
>> >
>> > Applied, thanks.
>>
>> Wait, I keeping this back after closer look.
>>
>> I think we have to remove this:
>>
>> if (nlh->nlmsg_len < NLMSG_HDRLEN || <---
>> skb->len < NLMSG_HDRLEN + sizeof(struct nfgenmsg))
>> return;
>>
>> in nfnetlink_rcv_skb_batch()
>>
>> now that we make this unfront check from nfnetlink_rcv().
>
> BTW, I can just mangle your patch here to delete such line to speed up
> things. See the mangled patch that is attached to this email.

Sure, I think the condition in nfnetlink_rcv_skb_batch() can be now
safely removed. Feel free to proceed with the mangled patch. Thanks.

Re: [PATCH v2] netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv

[Pablo Neira Ayuso]

On Tue, Jun 27, 2017 at 07:05:27PM +0200, Pablo Neira Ayuso wrote:
> On Tue, Jun 27, 2017 at 05:58:25PM +0200, Pablo Neira Ayuso wrote:
> > On Wed, Jun 07, 2017 at 03:50:38PM +0200, Mateusz Jurczyk wrote:
> > > Verify that the length of the socket buffer is sufficient to cover the
> > > nlmsghdr structure before accessing the nlh->nlmsg_len field for further
> > > input sanitization. If the client only supplies 1-3 bytes of data in
> > > sk_buff, then nlh->nlmsg_len remains partially uninitialized and
> > > contains leftover memory from the corresponding kernel allocation.
> > > Operating on such data may result in indeterminate evaluation of the
> > > nlmsg_len < NLMSG_HDRLEN expression.
> > > 
> > > The bug was discovered by a runtime instrumentation designed to detect
> > > use of uninitialized memory in the kernel. The patch prevents this and
> > > other similar tools (e.g. KMSAN) from flagging this behavior in the 
> > > future.
> > 
> > Applied, thanks.
> 
> Wait, I keeping this back after closer look.
> 
> I think we have to remove this:
> 
> if (nlh->nlmsg_len < NLMSG_HDRLEN || <---
> skb->len < NLMSG_HDRLEN + sizeof(struct nfgenmsg))
> return;
> 
> in nfnetlink_rcv_skb_batch()
> 
> now that we make this unfront check from nfnetlink_rcv().

BTW, I can just mangle your patch here to delete such line to speed up
things. See the mangled patch that is attached to this email.

Thanks.
diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index 80f5ecf2c3d7..ff1f4ce6fba4 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -463,8 +463,7 @@ static void nfnetlink_rcv_skb_batch(struct sk_buff *skb, struct nlmsghdr *nlh)
 	if (msglen > skb->len)
 		msglen = skb->len;
 
-	if (nlh->nlmsg_len < NLMSG_HDRLEN ||
-	skb->len < NLMSG_HDRLEN + sizeof(struct nfgenmsg))
+	if (skb->len < NLMSG_HDRLEN + sizeof(struct nfgenmsg))
 		return;
 
 	err = nla_parse(cda, NFNL_BATCH_MAX, attr, attrlen, nfnl_batch_policy,
@@ -491,7 +490,8 @@ static void nfnetlink_rcv(struct sk_buff *skb)
 {
 	struct nlmsghdr *nlh = nlmsg_hdr(skb);
 
-	if (nlh->nlmsg_len < NLMSG_HDRLEN ||
+	if (skb->len < NLMSG_HDRLEN ||
+	nlh->nlmsg_len < NLMSG_HDRLEN ||
 	skb->len < nlh->nlmsg_len)
 		return;
 

Re: [PATCH v2] netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv

[Pablo Neira Ayuso]

On Tue, Jun 27, 2017 at 05:58:25PM +0200, Pablo Neira Ayuso wrote:
> On Wed, Jun 07, 2017 at 03:50:38PM +0200, Mateusz Jurczyk wrote:
> > Verify that the length of the socket buffer is sufficient to cover the
> > nlmsghdr structure before accessing the nlh->nlmsg_len field for further
> > input sanitization. If the client only supplies 1-3 bytes of data in
> > sk_buff, then nlh->nlmsg_len remains partially uninitialized and
> > contains leftover memory from the corresponding kernel allocation.
> > Operating on such data may result in indeterminate evaluation of the
> > nlmsg_len < NLMSG_HDRLEN expression.
> > 
> > The bug was discovered by a runtime instrumentation designed to detect
> > use of uninitialized memory in the kernel. The patch prevents this and
> > other similar tools (e.g. KMSAN) from flagging this behavior in the future.
> 
> Applied, thanks.

Wait, I keeping this back after closer look.

I think we have to remove this:

if (nlh->nlmsg_len < NLMSG_HDRLEN || <---
skb->len < NLMSG_HDRLEN + sizeof(struct nfgenmsg))
return;

in nfnetlink_rcv_skb_batch()

now that we make this unfront check from nfnetlink_rcv().

P.S: Sorry I couldn't look at this any sooner, I've been busy in the
last weeks preparing things for the upcoming Netfilter Workshop.

Re: [PATCH v2] netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv

[Pablo Neira Ayuso]

On Wed, Jun 07, 2017 at 03:50:38PM +0200, Mateusz Jurczyk wrote:
> Verify that the length of the socket buffer is sufficient to cover the
> nlmsghdr structure before accessing the nlh->nlmsg_len field for further
> input sanitization. If the client only supplies 1-3 bytes of data in
> sk_buff, then nlh->nlmsg_len remains partially uninitialized and
> contains leftover memory from the corresponding kernel allocation.
> Operating on such data may result in indeterminate evaluation of the
> nlmsg_len < NLMSG_HDRLEN expression.
> 
> The bug was discovered by a runtime instrumentation designed to detect
> use of uninitialized memory in the kernel. The patch prevents this and
> other similar tools (e.g. KMSAN) from flagging this behavior in the future.

Applied, thanks.

[PATCH v2] netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv

[Mateusz Jurczyk]

Verify that the length of the socket buffer is sufficient to cover the
nlmsghdr structure before accessing the nlh->nlmsg_len field for further
input sanitization. If the client only supplies 1-3 bytes of data in
sk_buff, then nlh->nlmsg_len remains partially uninitialized and
contains leftover memory from the corresponding kernel allocation.
Operating on such data may result in indeterminate evaluation of the
nlmsg_len < NLMSG_HDRLEN expression.

The bug was discovered by a runtime instrumentation designed to detect
use of uninitialized memory in the kernel. The patch prevents this and
other similar tools (e.g. KMSAN) from flagging this behavior in the future.

Signed-off-by: Mateusz Jurczyk 
---
Changes in v2:
  - Compare skb->len against NLMSG_HDRLEN to avoid assuming the layout of
the nlmsghdr structure.

 net/netfilter/nfnetlink.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index 80f5ecf2c3d7..1f9667f52be5 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -491,7 +491,8 @@ static void nfnetlink_rcv(struct sk_buff *skb)
 {
struct nlmsghdr *nlh = nlmsg_hdr(skb);
 
-   if (nlh->nlmsg_len < NLMSG_HDRLEN ||
+   if (skb->len < NLMSG_HDRLEN ||
+   nlh->nlmsg_len < NLMSG_HDRLEN ||
skb->len < nlh->nlmsg_len)
return;
 
-- 
2.13.1.508.gb3defc5cc-goog