Bug 2541034 (CVE-2026-97936)

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

tracing: Fix memory corruption from the histogram stacktrace modifier

parse_field() sets HIST_FIELD_FL_STACKTRACE from the ".stacktrace"
modifier before it looks the field name up, and nothing afterwards
checks that the name resolved to a field which holds a stacktrace.
create_hist_field() picks HIST_FIELD_FN_STACK on the strength of the
field pointer alone, which reads a __data_loc word from the record and
follows its low 16 bits as an offset into the same record.
event_hist_trigger() takes the first word there as an entry count and
copies that many longs into a 31 entry array:

	n_entries = *stack;
	memcpy(entries, ++stack, n_entries * sizeof(unsigned long));

Neither end of that copy is bounded, and the count is whatever the event
holds at the offset, so any field will do:

  # cd /sys/kernel/tracing/events/sched/sched_process_fork
  # echo 'hist:keys=parent_pid.stacktrace' > trigger
  # (true)

  BUG: kernel NULL pointer dereference, address: 0000000000000008
  RIP: 0010:rb_insert_color+0x18/0x130
   timerqueue_linked_add+0x7e/0xd0
   enqueue_hrtimer+0x39/0xb0
   __hrtimer_run_queues+0x10f/0x1f0
   </IRQ>
  RIP: 0010:memcpy+0xc/0x30
   event_hist_trigger+0x165/0x690

The timer interrupt landed on the rbtree the copy had already run over.
No debug options are needed for this; KASAN reports the same write as an
out-of-bounds read of 13835058055416381440 bytes.

Documentation/trace/histogram.rst already states the rule, "must be a
long[] type", so enforce it once the name has been resolved. Names which
resolve to no field at all, "hitcount.stacktrace" and the common_*
pseudo-fields, are refused for the same reason: they hold no stacktrace
to read.