[PATCH] watchdog/perf: reject empty config before the raw event parse

[Bradley Morgan <brads@mainlining.org>]

Date: Fri, 2 Oct 2026 17:39:13 +0000
Subject: [PATCH] watchdog/perf: reject empty config before the raw event parse

Commit 6164be01f179 ("watchdog/perf: optimize bytes copied and remove
manual NUL-termination") replaced strscpy(buf, str, sizeof(buf)) plus a
manual buf[len] = 0 with strscpy(buf, str, len). strscpy() writes
nothing at all when the count is zero, so on a comma directly after
the "r" prefix, nmi_watchdog=r,1 for example, len is 0, buf stays
uninitialized, and kstrtoull() parses whatever stack garbage is there.

The old code was safe here by accident, strscpy() filled the whole
buffer before buf[len] = 0 overwrote the comma position, so a zero
length just produced an empty string and a clean parse failure.

Treat an empty config the same as an overlong one and return early.

Fixes: 6164be01f179 ("watchdog/perf: optimize bytes copied and remove manual NUL-termination")
Signed-off-by: Bradley Morgan <brads@mainlining.org>
---
 kernel/watchdog_perf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/watchdog_perf.c b/kernel/watchdog_perf.c
index cf05775a96d3..cca0485ba28c 100644
--- a/kernel/watchdog_perf.c
+++ b/kernel/watchdog_perf.c
@@ -301,7 +301,7 @@ void __init hardlockup_config_perf_event(const char *str)
 	} else {
 		unsigned int len = comma - str;
 
-		if (len > sizeof(buf))
+		if (!len || len > sizeof(buf))
 			return;
 
 		strscpy(buf, str, len);
-- 
2.53.0