From 988a35f8da1dec5a8cd2788054d1e717be61bf25 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Fri, 11 May 2018 19:54:19 +0900 Subject: [PATCH] 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 Cc: Steven Rostedt Cc: dvyukov@google.com Cc: syzkaller@googlegroups.com Cc: fengguang.wu@intel.com Cc: linux-kernel@vger.kernel.org Signed-off-by: Tetsuo Handa Fixes: 42a0bb3f71383b45 ("printk/nmi: generic solution for safe printk in NMI") Cc: 4.7+ # v4.7+ Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek --- kernel/printk/printk_safe.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c index 3e3c2004bb23..449d67edfa4b 100644 --- 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 @@ 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;