Commit cff2d762 authored by Jakub Kicinski's avatar Jakub Kicinski
Browse files

genetlink: reject use of nlmsg_flags for new commands 

Commit 9c5d03d3 ("genetlink: start to validate reserved header bytes")
introduced extra validation for genetlink headers. We had to gate it
to only apply to new commands, to maintain bug-wards compatibility.
Use this opportunity (before the new checks make it to Linus's tree)
to add more conditions.

Validate that Generic Netlink families do not use nlmsg_flags outside
of the well-understood set.

Link: https://lore.kernel.org/all/20220928073709.1b93b74a@kernel.org/


Reviewed-by: default avatarJohannes Berg <johannes@sipsolutions.net>
Acked-by: default avatarNikolay Aleksandrov <razor@blackwall.org>
Reviewed-by: default avatarNicolas Dichtel <nicolas.dichtel@6wind.com>
Reviewed-by: default avatarGuillaume Nault <gnault@redhat.com>
Reviewed-by: default avatarJacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20220929142809.1167546-1-kuba@kernel.org


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 915b96c5

net/netlink/genetlink.c

+31 −1
Original line number Diff line number Diff line
@@ -739,6 +739,36 @@ static int genl_family_rcv_msg_doit(const struct genl_family *family, 
	return err;

}



static int genl_header_check(const struct genl_family *family,

			     struct nlmsghdr *nlh, struct genlmsghdr *hdr,

			     struct netlink_ext_ack *extack)

{

	u16 flags;



	/* Only for commands added after we started validating */

	if (hdr->cmd < family->resv_start_op)

		return 0;



	if (hdr->reserved) {

		NL_SET_ERR_MSG(extack, "genlmsghdr.reserved field is not 0");

		return -EINVAL;

	}



	/* Old netlink flags have pretty loose semantics, allow only the flags

	 * consumed by the core where we can enforce the meaning.

	 */

	flags = nlh->nlmsg_flags;

	if ((flags & NLM_F_DUMP) == NLM_F_DUMP) /* DUMP is 2 bits */

		flags &= ~NLM_F_DUMP;

	if (flags & ~(NLM_F_REQUEST | NLM_F_ACK | NLM_F_ECHO)) {

		NL_SET_ERR_MSG(extack,

			       "ambiguous or reserved bits set in nlmsg_flags");

		return -EINVAL;

	}



	return 0;

}



static int genl_family_rcv_msg(const struct genl_family *family,

			       struct sk_buff *skb,

			       struct nlmsghdr *nlh,
@@ -757,7 +787,7 @@ static int genl_family_rcv_msg(const struct genl_family *family, 
	if (nlh->nlmsg_len < nlmsg_msg_size(hdrlen))

		return -EINVAL;



	if (hdr->cmd >= family->resv_start_op && hdr->reserved)

	if (genl_header_check(family, nlh, hdr, extack))

		return -EINVAL;



	if (genl_get_cmd(hdr->cmd, family, &op))