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Commit 988a35f8 authored by Tetsuo Handa's avatar Tetsuo Handa Committed by Petr Mladek
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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: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Fixes: 42a0bb3f ("printk/nmi: generic solution for safe printk in NMI")
Cc: 4.7+ <stable@vger.kernel.org> # v4.7+
Reviewed-by: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
parent 43a17111

kernel/printk/printk_safe.c

+4 −1
Original line number Diff line number Diff line
@@ -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;