[PATCH REPOST] printk: fix possible printk buffer overrun introduced with recursion check

[Tejun Heo <htejun@gmail.com>]

printk recursion detection prepends message to printk_buf and offsets
printk_buf when actual message is printed but it forgets to trim
buffer length accordingly.  This can result in buffer overrun in
extreme cases.

While at it, make printk_recursion_bug_msg static and move static
variables for recursion check into vprintk().

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
---
Eeeek, forgot to cc lkml last time.  Re-sending.  Sorry about the
noise.

 kernel/printk.c |   14 ++++++--------
 1 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/kernel/printk.c b/kernel/printk.c
index bee3610..074a3ea 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -613,15 +613,13 @@ asmlinkage int printk(const char *fmt, ...)
 	return r;
 }
 
-/* cpu currently holding logbuf_lock */
-static volatile unsigned int printk_cpu = UINT_MAX;
-
-const char printk_recursion_bug_msg [] =
-			KERN_CRIT "BUG: recent printk recursion!\n";
-static int printk_recursion_bug;
-
 asmlinkage int vprintk(const char *fmt, va_list args)
 {
+	/* cpu currently holding logbuf_lock */
+	static volatile unsigned int printk_cpu = UINT_MAX;
+	static const char printk_recursion_bug_msg [] =
+		KERN_CRIT "BUG: recent printk recursion!\n";
+	static int printk_recursion_bug;
 	static int log_level_unknown = 1;
 	static char printk_buf[1024];
 
@@ -666,7 +664,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 	}
 	/* Emit the output into the temporary buffer */
 	printed_len += vscnprintf(printk_buf + printed_len,
-				  sizeof(printk_buf), fmt, args);
+				  sizeof(printk_buf) - printed_len, fmt, args);
 
 	/*
 	 * Copy the output into log_buf.  If the caller didn't provide
-- 
1.5.2.4