CVE-2026-97921

Status: UPDATED  |  Advisory ID: CVE-2026-97921

Key Details

Affected Products, Subsystems & Sectors

What to Know

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

tracing: Free histogram the field rejected for a bad modifier

Writing a hist trigger whose value or variable carries a modifier that is

not allowed there leaks the fields that were built for it.

__create_val_field() takes the field from parse_expr() and stores it in

hist_data->fields[] only after the modifier checks have run:

hist_field = parse_expr(hist_data, file, field_str, flags, var_name,

&n_subexprs);

...

if (hist_field->flags & HIST_FIELD_FL_VAR) {

if (hist_field->flags & (...))

goto err;

} else {

if (hist_field->flags & (...))

goto err;

}

hist_data->fields[val_idx] = hist_field;

Both checks jump past that store, and the err label returns without

freeing anything. The error unwinds to create_hist_data(), which calls

destroy_hist_data() -> destroy_hist_fields(), and that reaches a field

only by walking fields[]. A field that never got there is unreachable.

commit e0213434fe3e ("tracing: Do not let histogram values have some

modifiers") set ret to -EINVAL and fell through to the store, which left

the field owned by fields[] and freed along with the rest of hist_data.

Splitting the check into a value case and a variable case replaced that

fall-through with a goto that skips it.

With CONFIG_DEBUG_KMEMLEAK, 200 writes of

# echo 'hist:keys=prev_pid:vals=next_pid.log2' > \

events/sched/sched_switch/trigger

each correctly rejected with -EINVAL, leave 332 unreferenced objects

(63744 bytes) reported at create_hist_field(); 200 install and remove

cycles of a valid trigger leave none. A '.log2' field is two

allocations, since create_hist_field() puts the plain field in

operands[0] of the log2 field, and both are reported.

Use destroy_hist_field() rather than __destroy_hist_field() so that

operands[0] is freed as well. It returns early for HIST_FIELD_FL_VAR_REF,

which is what an operand owned by hist_data->var_refs[] needs; the

rejected field itself is never a var ref, because a var ref never carries

a modifier flag. (NVD)

What to Do

Monitor Linux's web page for any future patch releases.

References