From: Matt Johnston matt@codeconstruct.com.au

commit f11cf946c0a92c560a890d68e4775723353599e1 upstream.

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: 583be982d934 ("mctp: Add device handling and netlink interface") Reported-by: syzbot+e76d52dadc089b9d197f@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68135815.050a0220.3a872c.000e.GAE@google.com/ Reported-by: syzbot+1065a199625a388fce60@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/681357d6.050a0220.14dd7d.000d.GAE@google.com/ Signed-off-by: Matt Johnston matt@codeconstruct.com.au Link: https://patch.msgid.link/20250508-mctp-addr-dump-v2-1-c8a53fd2dd66@codeconst... Signed-off-by: Jakub Kicinski kuba@kernel.org [ kovalev: bp to fix CVE-2025-38006 ] Signed-off-by: Vasiliy Kovalev kovalev@altlinux.org --- net/mctp/device.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/net/mctp/device.c b/net/mctp/device.c index 85cc5f31f1e7..27aee8b04055 100644 --- a/net/mctp/device.c +++ b/net/mctp/device.c @@ -119,12 +119,19 @@ 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; + int ifindex = 0; int idx = 0, rc;

- hdr = nlmsg_data(cb->nlh); - // filter by ifindex if requested - ifindex = hdr->ifa_index; + /* Filter by ifindex if a header is provided */ + if (cb->nlh->nlmsg_len >= nlmsg_msg_size(sizeof(*hdr))) { + hdr = nlmsg_data(cb->nlh); + 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 (; mcb->h < NETDEV_HASHENTRIES; mcb->h++, mcb->idx = 0) {