FAILED: patch "[PATCH] printk: fix possible reuse of va_list variable" failed to apply to 4.9-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 988a35f8da1dec5a8cd2788054d1e717be61bf25 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Fri, 11 May 2018 19:54:19 +0900
Subject: [PATCH] printk: fix possible reuse of va_list variable

I noticed that there is a possibility that printk_safe_log_store() causes
kernel oops because "args" parameter is passed to vsnprintf() again when
atomic_cmpxchg() detected that we raced. Fix this by using va_copy().

Link: http://lkml.kernel.org/r/201805112002.GIF21216.OFVHFOMLJtQFSO@I-love.SAKURA.ne.jp
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: dvyukov@google.com
Cc: syzkaller@googlegroups.com
Cc: fengguang.wu@intel.com
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Fixes: 42a0bb3f71383b45 ("printk/nmi: generic solution for safe printk in NMI")
Cc: 4.7+ <stable@vger.kernel.org> # v4.7+
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>

diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index 3e3c2004bb23..449d67edfa4b 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -82,6 +82,7 @@ static __printf(2, 0) int printk_safe_log_store(struct printk_safe_seq_buf *s,
 {
 	int add;
 	size_t len;
+	va_list ap;
 
 again:
 	len = atomic_read(&s->len);
@@ -100,7 +101,9 @@ static __printf(2, 0) int printk_safe_log_store(struct printk_safe_seq_buf *s,
 	if (!len)
 		smp_rmb();
 
-	add = vscnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, args);
+	va_copy(ap, args);
+	add = vscnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, ap);
+	va_end(ap);
 	if (!add)
 		return 0;