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Message-Id: <20250508-mctp-addr-dump-v2-1-c8a53fd2dd66@codeconstruct.com.au> Date: Thu, 08 May 2025 13:18:32 +0800 From: Matt Johnston <matt@...econstruct.com.au> To: Jeremy Kerr <jk@...econstruct.com.au>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org> Cc: netdev@...r.kernel.org, syzbot+e76d52dadc089b9d197f@...kaller.appspotmail.com, syzbot+1065a199625a388fce60@...kaller.appspotmail.com, Matt Johnston <matt@...econstruct.com.au> Subject: [PATCH net v2] 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: 583be982d934 ("mctp: Add device handling and netlink interface") Reported-by: syzbot+e76d52dadc089b9d197f@...kaller.appspotmail.com Closes: https://lore.kernel.org/all/68135815.050a0220.3a872c.000e.GAE@google.com/ Reported-by: syzbot+1065a199625a388fce60@...kaller.appspotmail.com Closes: https://lore.kernel.org/all/681357d6.050a0220.14dd7d.000d.GAE@google.com/ Signed-off-by: Matt Johnston <matt@...econstruct.com.au> --- Changes in v2: - Don't test for ifa_family=AF_MCTP - Fail if strict_check is set and header is short - Link to v1: https://lore.kernel.org/r/20250505-mctp-addr-dump-v1-1-a997013f99b8@codeconstruct.com.au --- 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 8e0724c56723de328592bfe5c6fc8085cd3102fe..7c0dcf3df3196207af6e1a1c002f388265c49fa1 100644 --- a/net/mctp/device.c +++ b/net/mctp/device.c @@ -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; - 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_each_netdev_dump(net, dev, mcb->ifindex) { --- base-commit: ebd297a2affadb6f6f4d2e5d975c1eda18ac762d change-id: 20250505-mctp-addr-dump-673e0fdc7894 Best regards, -- Matt Johnston <matt@...econstruct.com.au>
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