printk: fix possible reuse of va_list variable

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@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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index 3cdaeaef9ce1a63bfde3bc631946e40ed731e035..d989cc2381988e4574b76194bd7bf9e401ef4403 100644 (file)
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -85,6 +85,7 @@ 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);
@@ -103,7 +104,9 @@ again:
        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;