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/[email protected]
Cc: Peter Zijlstra <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Tetsuo Handa <[email protected]>
Fixes: 42a0bb3f71383b45 ("printk/nmi: generic solution for safe printk in NMI")
Cc: 4.7+ <[email protected]> # v4.7+
Reviewed-by: Sergey Senozhatsky <[email protected]>
Signed-off-by: Petr Mladek <[email protected]>

diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index 3e3c2004bb232661bae666e00e4645fad438aee6..449d67edfa4b3e41f07277937291b6614160db26 100644 (file)
--- 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 @@ 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;