decnet: dn_rtmsg: Improve input length sanitization in dnrmg_receive_user_skb
authorMateusz Jurczyk <mjurczyk@google.com>
Wed, 7 Jun 2017 13:14:29 +0000 (15:14 +0200)
committerDavid S. Miller <davem@davemloft.net>
Thu, 8 Jun 2017 14:38:54 +0000 (10:38 -0400)
commit85eac2ba35a2dbfbdd5767c7447a4af07444a5b4
treebe809e06a3e4330b99b82ed588b359f8e013cf87
parented66e50d9587fc0bb032e276a2563c0068a5b63a
decnet: dn_rtmsg: Improve input length sanitization in dnrmg_receive_user_skb

Verify that the length of the socket buffer is sufficient to cover the
entire nlh->nlmsg_len field before accessing that 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>
net/decnet/netfilter/dn_rtmsg.c