[v2] decnet: dn_rtmsg: Improve input length sanitization in dnrmg_receive_user_skb

Message ID 20170607141429.5781-1-mjurczyk@google.com
State Accepted
Delegated to: David Miller
Headers show

Commit Message

Mateusz Jurczyk June 7, 2017, 2:14 p.m.
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>
Changes in v2:
  - Compare skb->len against sizeof(*nlh) instead of sizeof(nlh->nlmsg_len)
    to avoid assuming the layout of the nlmsghdr structure. This was
    motivated by Eric Dumazet's comment on a related patch submission.

 net/decnet/netfilter/dn_rtmsg.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)


diff --git a/net/decnet/netfilter/dn_rtmsg.c b/net/decnet/netfilter/dn_rtmsg.c
index 1ed81ac6dd1a..aa8ffecc46a4 100644
--- a/net/decnet/netfilter/dn_rtmsg.c
+++ b/net/decnet/netfilter/dn_rtmsg.c
@@ -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)
 	if (!netlink_capable(skb, CAP_NET_ADMIN))