4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> Cc: dvyukov@xxxxxxxxxx Cc: syzkaller@xxxxxxxxxxxxxxxx Cc: fengguang.wu@xxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Fixes: 42a0bb3f71383b45 ("printk/nmi: generic solution for safe printk in NMI") Cc: 4.7+ <stable@xxxxxxxxxxxxxxx> # v4.7+ Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> Signed-off-by: Petr Mladek <pmladek@xxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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.
