Subject: CVE-2023-52906: net/sched: act_mpls: Fix warning during failed attribute validation

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

net/sched: act_mpls: Fix warning during failed attribute validation

The 'TCA_MPLS_LABEL' attribute is of 'NLA_U32' type, but has a
validation type of 'NLA_VALIDATE_FUNCTION'. This is an invalid
combination according to the comment above 'struct nla_policy':

"
Meaning of `validate' field, use via NLA_POLICY_VALIDATE_FN:
   NLA_BINARY           Validation function called for the attribute.
   All other            Unused - but note that it's a union
"

This can trigger the warning [1] in nla_get_range_unsigned() when
validation of the attribute fails. Despite being of 'NLA_U32' type, the
associated 'min'/'max' fields in the policy are negative as they are
aliased by the 'validate' field.

Fix by changing the attribute type to 'NLA_BINARY' which is consistent
with the above comment and all other users of NLA_POLICY_VALIDATE_FN().
As a result, move the length validation to the validation function.

No regressions in MPLS tests:

 # ./tdc.py -f tc-tests/actions/mpls.json
 [...]
 # echo $?
 0

[1]
WARNING: CPU: 0 PID: 17743 at lib/nlattr.c:118
nla_get_range_unsigned+0x1d8/0x1e0 lib/nlattr.c:117
Modules linked in:
CPU: 0 PID: 17743 Comm: syz-executor.0 Not tainted 6.1.0-rc8 #3
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.13.0-48-gd9c812dda519-prebuilt.qemu.org 04/01/2014
RIP: 0010:nla_get_range_unsigned+0x1d8/0x1e0 lib/nlattr.c:117
[...]
Call Trace:
 <TASK>
 __netlink_policy_dump_write_attr+0x23d/0x990 net/netlink/policy.c:310
 netlink_policy_dump_write_attr+0x22/0x30 net/netlink/policy.c:411
 netlink_ack_tlv_fill net/netlink/af_netlink.c:2454 [inline]
 netlink_ack+0x546/0x760 net/netlink/af_netlink.c:2506
 netlink_rcv_skb+0x1b7/0x240 net/netlink/af_netlink.c:2546
 rtnetlink_rcv+0x18/0x20 net/core/rtnetlink.c:6109
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x5e9/0x6b0 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x739/0x860 net/netlink/af_netlink.c:1921
 sock_sendmsg_nosec net/socket.c:714 [inline]
 sock_sendmsg net/socket.c:734 [inline]
 ____sys_sendmsg+0x38f/0x500 net/socket.c:2482
 ___sys_sendmsg net/socket.c:2536 [inline]
 __sys_sendmsg+0x197/0x230 net/socket.c:2565
 __do_sys_sendmsg net/socket.c:2574 [inline]
 __se_sys_sendmsg net/socket.c:2572 [inline]
 __x64_sys_sendmsg+0x42/0x50 net/socket.c:2572
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

The Linux kernel CVE team has assigned CVE-2023-52906 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.3 with commit 2a2ea50870ba and fixed in 5.4.229 with commit 2b157c3c5d6b
	Issue introduced in 5.3 with commit 2a2ea50870ba and fixed in 5.10.164 with commit 453277feb41c
	Issue introduced in 5.3 with commit 2a2ea50870ba and fixed in 5.15.89 with commit 9e2c38827cdc
	Issue introduced in 5.3 with commit 2a2ea50870ba and fixed in 6.1.7 with commit 8a97b544b98e
	Issue introduced in 5.3 with commit 2a2ea50870ba and fixed in 6.2 with commit 9e17f99220d1

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2023-52906
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	net/sched/act_mpls.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/2b157c3c5d6b8ddca48d53c9e662032f65af8d61
	https://git.kernel.org/stable/c/453277feb41c2235cf2c0de9209eef962c401457
	https://git.kernel.org/stable/c/9e2c38827cdc6fdd3bb375c8607fc04d289756f9
	https://git.kernel.org/stable/c/8a97b544b98e44f596219ebb290fd2ba2fd5d644
	https://git.kernel.org/stable/c/9e17f99220d111ea031b44153fdfe364b0024ff2