Commit f11cf946 authored by Matt Johnston's avatar Matt Johnston Committed by Jakub Kicinski
Browse files

net: mctp: Don't access ifa_index when missing 



In mctp_dump_addrinfo, ifa_index can be used to filter interfaces, but
only when the struct ifaddrmsg is provided. Otherwise it will be
comparing to uninitialised memory - reproducible in the syzkaller case from
dhcpd, or busybox "ip addr show".

The kernel MCTP implementation has always filtered by ifa_index, so
existing userspace programs expecting to dump MCTP addresses must
already be passing a valid ifa_index value (either 0 or a real index).

BUG: KMSAN: uninit-value in mctp_dump_addrinfo+0x208/0xac0 net/mctp/device.c:128
 mctp_dump_addrinfo+0x208/0xac0 net/mctp/device.c:128
 rtnl_dump_all+0x3ec/0x5b0 net/core/rtnetlink.c:4380
 rtnl_dumpit+0xd5/0x2f0 net/core/rtnetlink.c:6824
 netlink_dump+0x97b/0x1690 net/netlink/af_netlink.c:2309

Fixes: 583be982 ("mctp: Add device handling and netlink interface")
Reported-by: default avatar <syzbot+e76d52dadc089b9d197f@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/all/68135815.050a0220.3a872c.000e.GAE@google.com/


Reported-by: default avatar <syzbot+1065a199625a388fce60@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/all/681357d6.050a0220.14dd7d.000d.GAE@google.com/


Signed-off-by: default avatarMatt Johnston <matt@codeconstruct.com.au>
Link: https://patch.msgid.link/20250508-mctp-addr-dump-v2-1-c8a53fd2dd66@codeconstruct.com.au


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 45375814

net/mctp/device.c

+12 −5
Original line number Diff line number Diff line
@@ -117,11 +117,18 @@ static int mctp_dump_addrinfo(struct sk_buff *skb, struct netlink_callback *cb) 
	struct net_device *dev;

	struct ifaddrmsg *hdr;

	struct mctp_dev *mdev;

	int ifindex, rc;

	int ifindex = 0, rc;



	/* Filter by ifindex if a header is provided */

	if (cb->nlh->nlmsg_len >= nlmsg_msg_size(sizeof(*hdr))) {

		hdr = nlmsg_data(cb->nlh);

	// filter by ifindex if requested

		ifindex = hdr->ifa_index;

	} else {

		if (cb->strict_check) {

			NL_SET_ERR_MSG(cb->extack, "mctp: Invalid header for addr dump request");

			return -EINVAL;

		}

	}



	rcu_read_lock();

	for_each_netdev_dump(net, dev, mcb->ifindex) {