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tracing: Avoid NULL return from hist_field_name() on truncation

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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.

Link: https://patch.msgid.link/20260508195747.25492-1-devnexen@gmail.com
Fixes: 5ec1d1e97d ("tracing: Rebuild full_name on each hist_field_name() call")
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
David Carlier 2026-05-08 20:57:47 +01:00 committed by Steven Rostedt
parent 5200f5f493
commit 576ec047d2
1 changed files with 2 additions and 4 deletions
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6
kernel/trace/trace_events_hist.c
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@ -1369,10 +1369,8 @@ static const char *hist_field_name(struct hist_field *field,
len = snprintf(full_name, sizeof(full_name), fmt,
field->system, field->event_name,
field->name);
if (len >= sizeof(full_name))
return NULL;
field_name = full_name;
if (len < sizeof(full_name))
field_name = full_name;
} else
field_name = field->name;
} else if (field->flags & HIST_FIELD_FL_TIMESTAMP)