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linux/net/mctp
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Matt Johnston 8ef7b3f0db net: mctp: Don't access ifa_index when missing 
[ Upstream commit f11cf946c0 ]

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

[ The context change is due to the commit 2d45eeb7d5
("mctp: no longer rely on net->dev_index_head[]") in v6.14
which is irrelevant to the logic of this patch. ]

Fixes: 583be982d9 ("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@codeconstruct.com.au
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Johnny Hao <johnny_haocn@sina.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-04-18 10:33:35 +02:00
..
af_mctp.c net: mctp: Prevent duplicate binds 2025-08-28 16:24:20 +02:00
device.c net: mctp: Don't access ifa_index when missing 2026-04-18 10:33:35 +02:00
Kconfig mctp: Add MCTP base 2021-07-29 15:06:49 +01:00
Makefile mctp: Add neighbour implementation 2021-07-29 15:06:50 +01:00
neigh.c mctp: Handle error of rtnl_register_module(). 2024-10-17 15:11:57 +02:00
route.c mctp: Handle error of rtnl_register_module(). 2024-10-17 15:11:57 +02:00