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decnet: dn_rtmsg: Improve input length sanitization in dnrmg_receive_user_skb

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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 < sizeof(*nlh) 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: David S. Miller <davem@davemloft.net>
This commit is contained in:
Mateusz Jurczyk 2017-06-07 16:14:29 +02:00 committed by David S. Miller
parent c164772dd3
commit dd0da17b20
1 changed files with 3 additions and 1 deletions
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4
net/decnet/netfilter/dn_rtmsg.c
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@ -102,7 +102,9 @@ static inline void dnrmg_receive_user_skb(struct sk_buff *skb)
{
struct nlmsghdr *nlh = nlmsg_hdr(skb);
if (nlh->nlmsg_len < sizeof(*nlh) || skb->len < nlh->nlmsg_len)
if (skb->len < sizeof(*nlh) ||
nlh->nlmsg_len < sizeof(*nlh) ||
skb->len < nlh->nlmsg_len)
return;
if (!netlink_capable(skb, CAP_NET_ADMIN))