CVE-2026-97918

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

tracing: Undo the registration when enabling the histogram trigger fails

Commit 6f86bdeab633 ("tracing: Fix bad hist from corrupting named_triggers

list") described how a trigger that is registered but not on file->triggers

ends up freed while still on the global named_triggers list, and moved the

registration down so that hist_trigger_enable() follows it immediately. One

path still gets there. hist_trigger_enable() adds the trigger and takes it

straight back out when the event cannot be enabled:

list_add_tail_rcu(&data->list, &file->triggers);

update_cond_flag(file);

if (trace_event_trigger_enable_disable(file, 1) < 0) {

list_del_rcu(&data->list);

update_cond_flag(file);

ret--;

}

so the list walk in hist_unregister_trigger() matches nothing, test stays

NULL, and the ->free() that would call del_named_trigger() is skipped.

out_unreg falls through to out_free, which frees the trigger anyway:

BUG: KASAN: slab-use-after-free in find_named_trigger+0xac/0xc0

Read of size 8 at addr ffff8880091d3160 by task init/1

find_named_trigger+0xac/0xc0

hist_register_trigger+0xc1/0xa00

event_hist_trigger_parse+0x3146/0x6af0

event_trigger_write+0xce/0x160

Freed by task 69:

kfree+0x154/0x420

trigger_kthread_fn+0xfd/0x160

Leave the trigger where hist_unregister_trigger() can find it and let that

undo the registration, which is the only code that knows all of what

cmd_ops->init() took: the named list entry, the hist_pad reference, the

reference on the trigger a named histogram is shared with, and the copied

cmd_ops. It also pairs the failed trace_event_trigger_enable_disable(),

whose sm_ref and buffered event reference are otherwise left behind.

Since ->free() releases trigger_data and, for a trigger that does not share

its histogram, hist_data with it, out_unreg can no longer fall through to

out_free. For a trigger that does share, hist_register_trigger() has

already destroyed the caller's hist_data, so the fall-through was reading

freed memory there as well.

Move the enable_timestamps check in hist_unregister_trigger() above the

->free() call for the same reason: hist_data does not outlive it once the

trigger being removed is the one that owns it.