[PATCH AUTOSEL 6.0 32/77] netlink: Bounds-check struct nlmsgerr creation

Sasha Levin
2022-10-09T22:13:43Z

From: Kees Cook <keescook@chromium.org>

[ Upstream commit 710d21fdff9a98d621cd4e64167f3ef8af4e2fd1 ]

In preparation for FORTIFY_SOURCE doing bounds-check on memcpy(),
switch from __nlmsg_put to nlmsg_put(), and explain the bounds check
for dealing with the memcpy() across a composite flexible array struct.
Avoids this future run-time warning:

memcpy: detected field-spanning write (size 32) of single field "&errmsg->msg" at net/netlink/af_netlink.c:2447 (size 16)

Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Jozsef Kadlecsik <kadlec@netfilter.org>
Cc: Florian Westphal <fw@strlen.de>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: syzbot <syzkaller@googlegroups.com>
Cc: netfilter-devel@vger.kernel.org
Cc: coreteam@netfilter.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220901071336.1418572-1-keescook@chromium.org
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/ipset/ip_set_core.c | 8 +++++---
net/netlink/af_netlink.c | 8 +++++---
2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
index 16ae92054baa..6b31746f9be3 100644
--- a/net/netfilter/ipset/ip_set_core.c
+++ b/net/netfilter/ipset/ip_set_core.c
@@ -1719,11 +1719,13 @@ call_ad(struct net *net, struct sock *ctnl, struct sk_buff *skb,
skb2 = nlmsg_new(payload, GFP_KERNEL);
if (!skb2)
return -ENOMEM;
- rep = __nlmsg_put(skb2, NETLINK_CB(skb).portid,
- nlh->nlmsg_seq, NLMSG_ERROR, payload, 0);
+ rep = nlmsg_put(skb2, NETLINK_CB(skb).portid,
+ nlh->nlmsg_seq, NLMSG_ERROR, payload, 0);
errmsg = nlmsg_data(rep);
errmsg->error = ret;
- memcpy(&errmsg->msg, nlh, nlh->nlmsg_len);
+ unsafe_memcpy(&errmsg->msg, nlh, nlh->nlmsg_len,
+ /* Bounds checked by the skb layer. */);
+
cmdattr = (void *)&errmsg->msg + min_len;

ret = nla_parse(cda, IPSET_ATTR_CMD_MAX, cmdattr,
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 0cd91f813a3b..d8d3ed2096a3 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2440,11 +2440,13 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
return;
}

- rep = __nlmsg_put(skb, NETLINK_CB(in_skb).portid, nlh->nlmsg_seq,
- NLMSG_ERROR, payload, flags);
+ rep = nlmsg_put(skb, NETLINK_CB(in_skb).portid, nlh->nlmsg_seq,
+ NLMSG_ERROR, payload, flags);
errmsg = nlmsg_data(rep);
errmsg->error = err;
- memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) ? nlh->nlmsg_len : sizeof(*nlh));
+ unsafe_memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg)
+ ? nlh->nlmsg_len : sizeof(*nlh),
+ /* Bounds checked by the skb layer. */);

if (nlk_has_extack && extack) {
if (extack->_msg) {
--
2.35.1