Subject: CVE-2024-35893: net/sched: act_skbmod: prevent kernel-infoleak

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

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

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

net/sched: act_skbmod: prevent kernel-infoleak

syzbot found that tcf_skbmod_dump() was copying four bytes
from kernel stack to user space [1].

The issue here is that 'struct tc_skbmod' has a four bytes hole.

We need to clear the structure before filling fields.

[1]
BUG: KMSAN: kernel-infoleak in instrument_copy_to_user include/linux/instrumented.h:114 [inline]
 BUG: KMSAN: kernel-infoleak in copy_to_user_iter lib/iov_iter.c:24 [inline]
 BUG: KMSAN: kernel-infoleak in iterate_ubuf include/linux/iov_iter.h:29 [inline]
 BUG: KMSAN: kernel-infoleak in iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
 BUG: KMSAN: kernel-infoleak in iterate_and_advance include/linux/iov_iter.h:271 [inline]
 BUG: KMSAN: kernel-infoleak in _copy_to_iter+0x366/0x2520 lib/iov_iter.c:185
  instrument_copy_to_user include/linux/instrumented.h:114 [inline]
  copy_to_user_iter lib/iov_iter.c:24 [inline]
  iterate_ubuf include/linux/iov_iter.h:29 [inline]
  iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
  iterate_and_advance include/linux/iov_iter.h:271 [inline]
  _copy_to_iter+0x366/0x2520 lib/iov_iter.c:185
  copy_to_iter include/linux/uio.h:196 [inline]
  simple_copy_to_iter net/core/datagram.c:532 [inline]
  __skb_datagram_iter+0x185/0x1000 net/core/datagram.c:420
  skb_copy_datagram_iter+0x5c/0x200 net/core/datagram.c:546
  skb_copy_datagram_msg include/linux/skbuff.h:4050 [inline]
  netlink_recvmsg+0x432/0x1610 net/netlink/af_netlink.c:1962
  sock_recvmsg_nosec net/socket.c:1046 [inline]
  sock_recvmsg+0x2c4/0x340 net/socket.c:1068
  __sys_recvfrom+0x35a/0x5f0 net/socket.c:2242
  __do_sys_recvfrom net/socket.c:2260 [inline]
  __se_sys_recvfrom net/socket.c:2256 [inline]
  __x64_sys_recvfrom+0x126/0x1d0 net/socket.c:2256
 do_syscall_64+0xd5/0x1f0
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

Uninit was stored to memory at:
  pskb_expand_head+0x30f/0x19d0 net/core/skbuff.c:2253
  netlink_trim+0x2c2/0x330 net/netlink/af_netlink.c:1317
  netlink_unicast+0x9f/0x1260 net/netlink/af_netlink.c:1351
  nlmsg_unicast include/net/netlink.h:1144 [inline]
  nlmsg_notify+0x21d/0x2f0 net/netlink/af_netlink.c:2610
  rtnetlink_send+0x73/0x90 net/core/rtnetlink.c:741
  rtnetlink_maybe_send include/linux/rtnetlink.h:17 [inline]
  tcf_add_notify net/sched/act_api.c:2048 [inline]
  tcf_action_add net/sched/act_api.c:2071 [inline]
  tc_ctl_action+0x146e/0x19d0 net/sched/act_api.c:2119
  rtnetlink_rcv_msg+0x1737/0x1900 net/core/rtnetlink.c:6595
  netlink_rcv_skb+0x375/0x650 net/netlink/af_netlink.c:2559
  rtnetlink_rcv+0x34/0x40 net/core/rtnetlink.c:6613
  netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
  netlink_unicast+0xf4c/0x1260 net/netlink/af_netlink.c:1361
  netlink_sendmsg+0x10df/0x11f0 net/netlink/af_netlink.c:1905
  sock_sendmsg_nosec net/socket.c:730 [inline]
  __sock_sendmsg+0x30f/0x380 net/socket.c:745
  ____sys_sendmsg+0x877/0xb60 net/socket.c:2584
  ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2638
  __sys_sendmsg net/socket.c:2667 [inline]
  __do_sys_sendmsg net/socket.c:2676 [inline]
  __se_sys_sendmsg net/socket.c:2674 [inline]
  __x64_sys_sendmsg+0x307/0x4a0 net/socket.c:2674
 do_syscall_64+0xd5/0x1f0
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

Uninit was stored to memory at:
  __nla_put lib/nlattr.c:1041 [inline]
  nla_put+0x1c6/0x230 lib/nlattr.c:1099
  tcf_skbmod_dump+0x23f/0xc20 net/sched/act_skbmod.c:256
  tcf_action_dump_old net/sched/act_api.c:1191 [inline]
  tcf_action_dump_1+0x85e/0x970 net/sched/act_api.c:1227
  tcf_action_dump+0x1fd/0x460 net/sched/act_api.c:1251
  tca_get_fill+0x519/0x7a0 net/sched/act_api.c:1628
  tcf_add_notify_msg net/sched/act_api.c:2023 [inline]
  tcf_add_notify net/sched/act_api.c:2042 [inline]
  tcf_action_add net/sched/act_api.c:2071 [inline]
  tc_ctl_action+0x1365/0x19d0 net/sched/act_api.c:2119
  rtnetlink_rcv_msg+0x1737/0x1900 net/core/rtnetlink.c:6595
  netlink_rcv_skb+0x375/0x650 net/netlink/af_netlink.c:2559
  rtnetlink_rcv+0x34/0x40 net/core/rtnetlink.c:6613
  netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
  netlink_unicast+0xf4c/0x1260 net/netlink/af_netlink.c:1361
  netlink_sendmsg+0x10df/0x11f0 net/netlink/af_netlink.c:1905
  sock_sendmsg_nosec net/socket.c:730 [inline]
  __sock_sendmsg+0x30f/0x380 net/socket.c:745
  ____sys_sendmsg+0x877/0xb60 net/socket.c:2584
  ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2638
  __sys_sendmsg net/socket.c:2667 [inline]
  __do_sys_sendmsg net/socket.c:2676 [inline]
  __se_sys_sendmsg net/socket.c:2674 [inline]
  __x64_sys_sendmsg+0x307/0x4a0 net/socket.c:2674
 do_syscall_64+0xd5/0x1f0
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

Local variable opt created at:
  tcf_skbmod_dump+0x9d/0xc20 net/sched/act_skbmod.c:244
  tcf_action_dump_old net/sched/act_api.c:1191 [inline]
  tcf_action_dump_1+0x85e/0x970 net/sched/act_api.c:1227

Bytes 188-191 of 248 are uninitialized
Memory access of size 248 starts at ffff888117697680
Data copied to user address 00007ffe56d855f0

The Linux kernel CVE team has assigned CVE-2024-35893 to this issue.

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

	Issue introduced in 4.9 with commit 86da71b57383 and fixed in 4.19.312 with commit f190a4aa03cb
	Issue introduced in 4.9 with commit 86da71b57383 and fixed in 5.4.274 with commit f356eb2fb567
	Issue introduced in 4.9 with commit 86da71b57383 and fixed in 5.10.215 with commit 5e45dc440885
	Issue introduced in 4.9 with commit 86da71b57383 and fixed in 5.15.154 with commit a097fc199ab5
	Issue introduced in 4.9 with commit 86da71b57383 and fixed in 6.1.85 with commit 55d3fe7b2b7b
	Issue introduced in 4.9 with commit 86da71b57383 and fixed in 6.6.26 with commit 729ad2ac2a2c
	Issue introduced in 4.9 with commit 86da71b57383 and fixed in 6.8.5 with commit 7bb2c7103d8c
	Issue introduced in 4.9 with commit 86da71b57383 and fixed in 6.9 with commit d313eb8b7755

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-2024-35893
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_skbmod.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/f190a4aa03cbd518bd9c62a66e1233984f5fd2ec
	https://git.kernel.org/stable/c/f356eb2fb567e0931143ac1769ac802d3b3e2077
	https://git.kernel.org/stable/c/5e45dc4408857305f4685abfd7a528a1e58b51b5
	https://git.kernel.org/stable/c/a097fc199ab5f4b5392c5144034c0d2148b55a14
	https://git.kernel.org/stable/c/55d3fe7b2b7bc354e7cbc1f7b8f98a29ccd5a366
	https://git.kernel.org/stable/c/729ad2ac2a2cdc9f4a4bdfd40bfd276e6bc33924
	https://git.kernel.org/stable/c/7bb2c7103d8c13b06a57bf997b8cdbe93cd7283c
	https://git.kernel.org/stable/c/d313eb8b77557a6d5855f42d2234bd592c7b50dd