CVE-2026-64028

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

tracing: Avoid NULL return from hist_field_name() on truncation

hist_field_name() returns "" everywhere except the fully-qualified

VAR_REF/EXPR case, where snprintf() truncation returns NULL early

and bypasses the bottom NULL->"" guard. Callers don't expect NULL:

strcat(expr, hist_field_name(field, 0)) at trace_events_hist.c:1758

and the strcmp() in the sort-key match loop at :4804 both deref it.

system and event_name are bounded by MAX_EVENT_NAME_LEN, but the

field name on a VAR_REF is kstrdup'd from a histogram variable

name parsed out of the trigger string and has no length cap, so

a long enough var name in a fully qualified reference can reach

the truncation path.

Keep the length check but leave field_name as "" on overflow.