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