net: mctp: Don't access ifa_index when missing

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: 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

References

• https://git.kernel.org/stable/c/8ef7b3f0db69e2f4a80be351f6aee9a4c2332ef9
• https://git.kernel.org/stable/c/acab78ae12c7fefb4f3bfe22e00770a5faa42724
• https://git.kernel.org/stable/c/d4d1561d17eb72908e4489c0900d96e0484fac20
• https://git.kernel.org/stable/c/24fa213dffa470166ec014f979f36c6ff44afb45
• https://git.kernel.org/stable/c/f11cf946c0a92c560a890d68e4775723353599e1