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From: Josh Law <objecting@objecting.org>
To: Petr Mladek <pmladek@suse.com>, Steven Rostedt <rostedt@goodmis.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Josh Law <objecting@objecting.org>,
	linux-kernel@vger.kernel.org
Subject: [PATCH 1/4] lib/vsprintf: always advance args in bstr_printf() pointer path
Date: Tue, 24 Mar 2026 22:49:37 +0000	[thread overview]
Message-ID: <20260324224940.50508-2-objecting@objecting.org> (raw)
In-Reply-To: <20260324224940.50508-1-objecting@objecting.org>

When the output buffer is full (str >= end), bstr_printf() skips
advancing the args pointer past the pre-rendered pointer string in
bin_buf. This causes all subsequent format specifiers to read from
the wrong position, corrupting the rest of the output.

Always compute the string length and advance args regardless of
whether there is space to copy into the output buffer.

Signed-off-by: Josh Law <objecting@objecting.org>
---
 lib/vsprintf.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 800b8ac49f53..7898fb998b21 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -3389,14 +3389,15 @@ int bstr_printf(char *buf, size_t size, const char *fmt_str, const u32 *bin_buf)
 					break;
 				}
 				/* Pointer dereference was already processed */
+				len = strlen(args);
 				if (str < end) {
-					len = copy = strlen(args);
+					copy = len;
 					if (copy > end - str)
 						copy = end - str;
 					memcpy(str, args, copy);
-					str += len;
-					args += len + 1;
 				}
+				str += len;
+				args += len + 1;
 			}
 			if (process)
 				str = pointer(fmt.str, str, end, get_arg(void *), spec);
-- 
2.34.1


  reply	other threads:[~2026-03-24 22:50 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-03-24 22:49 [PATCH 0/4] lib/vsprintf: assorted bug fixes Josh Law
2026-03-24 22:49 ` Josh Law [this message]
2026-03-30 16:06   ` [PATCH 1/4] lib/vsprintf: always advance args in bstr_printf() pointer path Petr Mladek
2026-03-24 22:49 ` [PATCH 2/4] lib/vsprintf: fix OOB write in vbin_printf() when size is zero Josh Law
2026-03-30 16:17   ` Petr Mladek
2026-03-30 16:31   ` Steven Rostedt
2026-03-30 16:32     ` Josh Law
2026-03-30 16:32     ` Josh Law
2026-03-30 16:32     ` Josh Law
2026-03-30 16:34     ` Josh Law
2026-03-24 22:49 ` [PATCH 3/4] lib/vsprintf: use int for field_width in vsscanf() Josh Law
2026-03-25 12:00   ` Andy Shevchenko
2026-03-31 14:31     ` Petr Mladek
2026-03-31 15:35       ` David Laight
2026-03-31 16:12         ` Petr Mladek
2026-03-31 16:13           ` Josh Law
2026-03-31 16:13           ` Josh Law
2026-03-31 16:13           ` Josh Law
2026-04-01 14:22           ` David Laight
2026-04-01 18:29             ` David Laight
2026-03-24 22:49 ` [PATCH 4/4] lib/vsprintf: add missing (u8) cast in format_decode() lookup Josh Law
2026-03-25 12:02   ` Andy Shevchenko
2026-03-31 14:33   ` Petr Mladek
2026-03-31 14:44     ` Josh Law
2026-03-31 14:44     ` Josh Law
2026-03-25 12:05 ` [PATCH 0/4] lib/vsprintf: assorted bug fixes Andy Shevchenko
2026-03-25 17:20   ` Josh Law

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