Re: [PATCH 01/32] netlink: Avoid memcpy() across flexible array boundary
From: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Date: 2022-05-04 03:22:15
Also in:
keyrings, linux-arm-msm, linux-bluetooth, linux-devicetree, linux-hardening, linux-hyperv, linux-integrity, linux-rdma, linux-scsi, linux-security-module, linux-usb, linux-wireless, llvm, selinux, xen-devel
Subsystem:
netfilter, networking [general], the rest · Maintainers:
Pablo Neira Ayuso, Florian Westphal, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
On Tue, May 03, 2022 at 06:44:10PM -0700, Kees Cook wrote:
quoted hunk ↗ jump to hunk
In preparation for run-time memcpy() bounds checking, split the nlmsg copying for error messages (which crosses a previous unspecified flexible array boundary) in half. Avoids the future run-time warning: memcpy: detected field-spanning write (size 32) of single field "&errmsg->msg" (size 16) Creates an explicit flexible array at the end of nlmsghdr for the payload, named "nlmsg_payload". There is no impact on UAPI; the sizeof(struct nlmsghdr) does not change, but now the compiler can better reason about where things are being copied. Fixed-by: Rasmus Villemoes [off-list ref] Link: https://lore.kernel.org/lkml/d7251d92-150b-5346-6237-52afc154bb00@rasmusvillemoes.dk (local) Cc: "David S. Miller" <davem@davemloft.net> Cc: Jakub Kicinski <kuba@kernel.org> Cc: Rich Felker <redacted> Cc: Eric Dumazet <edumazet@google.com> Cc: netdev@vger.kernel.org Signed-off-by: Kees Cook <redacted> --- include/uapi/linux/netlink.h | 1 + net/netlink/af_netlink.c | 5 ++++- 2 files changed, 5 insertions(+), 1 deletion(-)diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h index 855dffb4c1c3..47f9342d51bc 100644 --- a/include/uapi/linux/netlink.h +++ b/include/uapi/linux/netlink.h@@ -47,6 +47,7 @@ struct nlmsghdr { __u16 nlmsg_flags; /* Additional flags */ __u32 nlmsg_seq; /* Sequence number */ __u32 nlmsg_pid; /* Sending process port ID */ + __u8 nlmsg_payload[];/* Contents of message */ }; /* Flags values */diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 1b5a9c2e1c29..09346aee1022 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c@@ -2445,7 +2445,10 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err, NLMSG_ERROR, payload, flags); errmsg = nlmsg_data(rep); errmsg->error = err; - memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) ? nlh->nlmsg_len : sizeof(*nlh)); + errmsg->msg = *nlh; + if (payload > sizeof(*errmsg)) + memcpy(errmsg->msg.nlmsg_payload, nlh->nlmsg_payload, + nlh->nlmsg_len - sizeof(*nlh));
They have nlmsg_len()[1] for the length of the payload without the header:
/**
* nlmsg_len - length of message payload
* @nlh: netlink message header
*/
static inline int nlmsg_len(const struct nlmsghdr *nlh)
{
return nlh->nlmsg_len - NLMSG_HDRLEN;
}
(would that function use some sanitization, though? what if nlmsg_len is
somehow manipulated to be less than NLMSG_HDRLEN?...)
Also, it seems there is at least one more instance of this same issue:
diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
index 16ae92054baa..d06184b94af5 100644
--- a/net/netfilter/ipset/ip_set_core.c
+++ b/net/netfilter/ipset/ip_set_core.c@@ -1723,7 +1723,8 @@ call_ad(struct net *net, struct sock *ctnl, struct sk_buff *skb, nlh->nlmsg_seq, NLMSG_ERROR, payload, 0); errmsg = nlmsg_data(rep); errmsg->error = ret; - memcpy(&errmsg->msg, nlh, nlh->nlmsg_len); + errmsg->msg = *nlh; + memcpy(errmsg->msg.nlmsg_payload, nlh->nlmsg_payload, nlmsg_len(nlh)); cmdattr = (void *)&errmsg->msg + min_len; ret = nla_parse(cda, IPSET_ATTR_CMD_MAX, cmdattr, --
Gustavo [1] https://elixir.bootlin.com/linux/v5.18-rc5/source/include/net/netlink.h#L577