High · published December 30, 2025
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
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