linux-kernel - [PATCH v2 26/32] tools/nolibc: allow limiting of printf destination size

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20250407-nolibc-kselftest-harness-v2-26-f8812f76e930@linutronix.de>
Date: Mon, 07 Apr 2025 08:52:49 +0200
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Shuah Khan <shuah@...nel.org>, Shuah Khan <skhan@...uxfoundation.org>, 
 Willy Tarreau <w@....eu>, 
 Thomas Weißschuh <linux@...ssschuh.net>
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: [PATCH v2 26/32] tools/nolibc: allow limiting of printf
 destination size

snprintf() allows limiting the output buffer, while still returning the
number of all bytes that would have been written.
Implement the limitation logic in preparation for snprintf().

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Acked-by: Willy Tarreau <w@....eu>
---
 tools/include/nolibc/stdio.h | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index 5c893b4903a3040a366e11b600ccde30913d7db2..b17b473bd8751a6283309178b4848e61e1683305 100644
--- a/tools/include/nolibc/stdio.h
+++ b/tools/include/nolibc/stdio.h
@@ -215,13 +215,13 @@ char *fgets(char *s, int size, FILE *stream)
  */
 typedef int (*__nolibc_printf_cb)(intptr_t state, const char *buf, size_t size);
 
-static __attribute__((unused, format(printf, 3, 0)))
-int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, const char *fmt, va_list args)
+static __attribute__((unused, format(printf, 4, 0)))
+int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, size_t n, const char *fmt, va_list args)
 {
 	char escape, lpref, c;
 	unsigned long long v;
 	unsigned int written;
-	size_t len, ofs;
+	size_t len, ofs, w;
 	char tmpbuf[21];
 	const char *outstr;
 
@@ -306,8 +306,12 @@ int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, const char *fmt, va_l
 			outstr = fmt;
 			len = ofs - 1;
 		flush_str:
-			if (cb(state, outstr, len) != 0)
-				break;
+			if (n) {
+				w = len < n ? len : n;
+				n -= w;
+				if (cb(state, outstr, w) != 0)
+					break;
+			}
 
 			written += len;
 		do_escape:
@@ -331,7 +335,7 @@ static int __nolibc_fprintf_cb(intptr_t state, const char *buf, size_t size)
 static __attribute__((unused, format(printf, 2, 0)))
 int vfprintf(FILE *stream, const char *fmt, va_list args)
 {
-	return __nolibc_printf(__nolibc_fprintf_cb, (intptr_t)stream, fmt, args);
+	return __nolibc_printf(__nolibc_fprintf_cb, (intptr_t)stream, SIZE_MAX, fmt, args);
 }
 
 static __attribute__((unused, format(printf, 1, 0)))

-- 
2.49.0