CVE-2024-35893

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_netli

---truncated---