linux-kernel - [PATCH 1/2] tomoyo: use vsnprintf() properly

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Message-ID: <YwFDLhioFG5Mlwws@ZenIV>
Date:   Sat, 20 Aug 2022 21:25:18 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] tomoyo: use vsnprintf() properly

Idiomatic way to find how much space sprintf output would take is
	len = snprintf(NULL, 0, ...) + 1;
Once upon a time there'd been libc implementations that blew chunks
on that and somebody had come up with the following "cute" trick:
	len = snprintf((char *) &len, 1, ...) + 1;
for doing the same.  However, that's unidiomatic, harder to follow
*and* any such libc implementation would violate both C99 and POSIX
(since 2001).
	IOW, this kludge is best buried along with such libc implementations,
nevermind getting cargo-culted into newer code.  Our vsnprintf() does not
suffer that braindamage, TYVM.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 security/tomoyo/audit.c  | 2 +-
 security/tomoyo/common.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/security/tomoyo/audit.c b/security/tomoyo/audit.c
index 023bedd9dfa3..7cf8fdbb29bf 100644
--- a/security/tomoyo/audit.c
+++ b/security/tomoyo/audit.c
@@ -423,7 +423,7 @@ void tomoyo_write_log(struct tomoyo_request_info *r, const char *fmt, ...)
 	int len;
 
 	va_start(args, fmt);
-	len = vsnprintf((char *) &len, 1, fmt, args) + 1;
+	len = vsnprintf(NULL, 0, fmt, args) + 1;
 	va_end(args);
 	va_start(args, fmt);
 	tomoyo_write_log2(r, len, fmt, args);
diff --git a/security/tomoyo/common.c b/security/tomoyo/common.c
index ff17abc96e5c..f4cd9b58b205 100644
--- a/security/tomoyo/common.c
+++ b/security/tomoyo/common.c
@@ -2057,7 +2057,7 @@ int tomoyo_supervisor(struct tomoyo_request_info *r, const char *fmt, ...)
 	bool quota_exceeded = false;
 
 	va_start(args, fmt);
-	len = vsnprintf((char *) &len, 1, fmt, args) + 1;
+	len = vsnprintf(NULL, 0, fmt, args) + 1;
 	va_end(args);
 	/* Write /sys/kernel/security/tomoyo/audit. */
 	va_start(args, fmt);
-- 
2.30.2