linux-kernel - [PATCH 4.9 049/101] printk: fix possible reuse of va

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Date:   Sun,  1 Jul 2018 18:21:35 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>, dvyukov@...gle.com,
        syzkaller@...glegroups.com, fengguang.wu@...el.com,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>
Subject: [PATCH 4.9 049/101] printk: fix possible reuse of va_list variable

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

commit 988a35f8da1dec5a8cd2788054d1e717be61bf25 upstream.

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@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: dvyukov@...gle.com
Cc: syzkaller@...glegroups.com
Cc: fengguang.wu@...el.com
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Fixes: 42a0bb3f71383b45 ("printk/nmi: generic solution for safe printk in NMI")
Cc: 4.7+ <stable@...r.kernel.org> # v4.7+
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Signed-off-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/printk/nmi.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/kernel/printk/nmi.c
+++ b/kernel/printk/nmi.c
@@ -63,6 +63,7 @@ static int vprintk_nmi(const char *fmt,
 	struct nmi_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
 	int add = 0;
 	size_t len;
+	va_list ap;
 
 again:
 	len = atomic_read(&s->len);
@@ -79,7 +80,9 @@ again:
 	if (!len)
 		smp_rmb();
 
-	add = vsnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, args);
+	va_copy(ap, args);
+	add = vsnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, ap);
+	va_end(ap);
 
 	/*
 	 * Do it once again if the buffer has been flushed in the meantime.