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printk: fix possible reuse of va_list variable 

commit 988a35f8da 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: 42a0bb3f71 ("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>
pull/10/head
Tetsuo Handa 2018-05-11 19:54:19 +09:00 committed by Greg Kroah-Hartman
parent affd84024c
commit a47c3c4876
1 changed files with 4 additions and 1 deletions
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5
kernel/printk/printk_safe.c
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@ -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;