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netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv

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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 <mjurczyk@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Mateusz Jurczyk 2017-06-07 15:50:38 +02:00 committed by Pablo Neira Ayuso
parent 533da29b58
commit f55ce7b024
1 changed files with 3 additions and 3 deletions
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6
net/netfilter/nfnetlink.c
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@ -472,8 +472,7 @@ static void nfnetlink_rcv_skb_batch(struct sk_buff *skb, struct nlmsghdr *nlh)
if (msglen > skb->len) if (msglen > skb->len)
msglen = skb->len; msglen = skb->len;
if (nlh->nlmsg_len < NLMSG_HDRLEN || if (skb->len < NLMSG_HDRLEN + sizeof(struct nfgenmsg))
skb->len < NLMSG_HDRLEN + sizeof(struct nfgenmsg))
return; return;
err = nla_parse(cda, NFNL_BATCH_MAX, attr, attrlen, nfnl_batch_policy, err = nla_parse(cda, NFNL_BATCH_MAX, attr, attrlen, nfnl_batch_policy,
@ -500,7 +499,8 @@ static void nfnetlink_rcv(struct sk_buff *skb)
{ {
struct nlmsghdr *nlh = nlmsg_hdr(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) skb->len < nlh->nlmsg_len)
return; return;