net/sched: cls_api: remove block_cb from driver_list before freeing
CVE: CVE-2023-54193
Component: kernel
CWE: CWE-416
Severity: Moderate
CVSS v3: 6.2/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H
Release date: 2023-01-01T00:00:00+00:00

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

net/sched: cls_api: remove block_cb from driver_list before freeing

Error handler of tcf_block_bind() frees the whole bo->cb_list on error.
However, by that time the flow_block_cb instances are already in the driver
list because driver ndo_setup_tc() callback is called before that up the
call chain in tcf_block_offload_cmd(). This leaves dangling pointers to
freed objects in the list and causes use-after-free[0]. Fix it by also
removing flow_block_cb instances from driver_list before deallocating them.

[0]:
[  279.868433] ==================================================================
[  279.869964] BUG: KASAN: slab-use-after-free in flow_block_cb_setup_simple+0x631/0x7c0
[  279.871527] Read of size 8 at addr ffff888147e2bf20 by task tc/2963

[  279.873151] CPU: 6 PID: 2963 Comm: tc Not tainted 6.3.0-rc6+ #4
[  279.874273] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
[  279.876295] Call Trace:
[  279.876882]  <TASK>
[  279.877413]  dump_stack_lvl+0x33/0x50
[  279.878198]  print_report+0xc2/0x610
[  279.878987]  ? flow_block_cb_setup_simple+0x631/0x7c0
[  279.879994]  kasan_report+0xae/0xe0
[  279.880750]  ? flow_block_cb_setup_simple+0x631/0x7c0
[  279.881744]  ? mlx5e_tc_reoffload_flows_work+0x240/0x240 [mlx5_core]
[  279.883047]  flow_block_cb_setup_simple+0x631/0x7c0
[  279.884027]  tcf_block_offload_cmd.isra.0+0x189/0x2d0
[  279.885037]  ? tcf_block_setup+0x6b0/0x6b0
[  279.885901]  ? mutex_lock+0x7d/0xd0
[  279.886669]  ? __mutex_unlock_slowpath.constprop.0+0x2d0/0x2d0
[  279.887844]  ? ingress_init+0x1c0/0x1c0 [sch_ingress]
[  279.888846]  tcf_block_get_ext+0x61c/0x1200
[  279.889711]  ingress_init+0x112/0x1c0 [sch_ingress]
[  279.890682]  ? clsact_init+0x2b0/0x2b0 [sch_ingress]
[  279.891701]  qdisc_create+0x401/0xea0
[  279.892485]  ? qdisc_tree_reduce_backlog+0x470/0x470
[  279.893473]  tc_modify_qdisc+0x6f7/0x16d0
[  279.894344]  ? tc_get_qdisc+0xac0/0xac0
[  279.895213]  ? mutex_lock+0x7d/0xd0
[  279.896005]  ? __mutex_lock_slowpath+0x10/0x10
[  279.896910]  rtnetlink_rcv_msg+0x5fe/0x9d0
[  279.897770]  ? rtnl_calcit.isra.0+0x2b0/0x2b0
[  279.898672]  ? __sys_sendmsg+0xb5/0x140
[  279.899494]  ? do_syscall_64+0x3d/0x90
[  279.900302]  ? entry_SYSCALL_64_after_hwframe+0x46/0xb0
[  279.901337]  ? kasan_save_stack+0x2e/0x40
[  279.902177]  ? kasan_save_stack+0x1e/0x40
[  279.903058]  ? kasan_set_track+0x21/0x30
[  279.903913]  ? kasan_save_free_info+0x2a/0x40
[  279.904836]  ? ____kasan_slab_free+0x11a/0x1b0
[  279.905741]  ? kmem_cache_free+0x179/0x400
[  279.906599]  netlink_rcv_skb+0x12c/0x360
[  279.907450]  ? rtnl_calcit.isra.0+0x2b0/0x2b0
[  279.908360]  ? netlink_ack+0x1550/0x1550
[  279.909192]  ? rhashtable_walk_peek+0x170/0x170
[  279.910135]  ? kmem_cache_alloc_node+0x1af/0x390
[  279.911086]  ? _copy_from_iter+0x3d6/0xc70
[  279.912031]  netlink_unicast+0x553/0x790
[  279.912864]  ? netlink_attachskb+0x6a0/0x6a0
[  279.913763]  ? netlink_recvmsg+0x416/0xb50
[  279.914627]  netlink_sendmsg+0x7a1/0xcb0
[  279.915473]  ? netlink_unicast+0x790/0x790
[  279.916334]  ? iovec_from_user.part.0+0x4d/0x220
[  279.917293]  ? netlink_unicast+0x790/0x790
[  279.918159]  sock_sendmsg+0xc5/0x190
[  279.918938]  ____sys_sendmsg+0x535/0x6b0
[  279.919813]  ? import_iovec+0x7/0x10
[  279.920601]  ? kernel_sendmsg+0x30/0x30
[  279.921423]  ? __copy_msghdr+0x3c0/0x3c0
[  279.922254]  ? import_iovec+0x7/0x10
[  279.923041]  ___sys_sendmsg+0xeb/0x170
[  279.923854]  ? copy_msghdr_from_user+0x110/0x110
[  279.924797]  ? ___sys_recvmsg+0xd9/0x130
[  279.925630]  ? __perf_event_task_sched_in+0x183/0x470
[  279.926656]  ? ___sys_sendmsg+0x170/0x170
[  279.927529]  ? ctx_sched_in+0x530/0x530
[  279.928369]  ? update_curr+0x283/0x4f0
[  279.929185]  ? perf_event_update_userpage+0x570/0x570
[  279.930201]  ? __fget_light+0x57/0x520
[  279.931023]  ? __switch_to+0x53d/0xe70
[  27
---truncated---

Statement: This bug is a use-after-free caused by leaving flow_block_cb pointers in driver_list after the error path frees the callback objects, leading to dangling references later accessed in flow_block_cb_setup_simple(). A highly privileged local attacker (typically CAP_NET_ADMIN via tc/rtnetlink) can reliably trigger kernel crashes (DoS), potentially taking down the host. While kernel UAFs are theoretically exploitable, the prerequisite privileges and control surface make practical LPE/RCE unlikely here.

Remediation: