ALSA: info: Drop WARN_ON() from buffer NULL sanity check

snd_info_get_line() has a sanity check of NULL buffer -- both buffer
itself being NULL and buffer->buffer being NULL.  Basically both
checks are valid and necessary, but the problem is that it's with
snd_BUG_ON() macro that triggers WARN_ON().  The latter condition
(NULL buffer->buffer) can be met arbitrarily by user since the buffer
is allocated at the first write, so it means that user can trigger
WARN_ON() at will.

This patch addresses it by simply moving buffer->buffer NULL check out
of snd_BUG_ON() so that spurious WARNING is no longer triggered.

Reported-by: syzbot+e42d0746c3c3699b6061@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200717084023.5928-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/core/info.c b/sound/core/info.c
index 8c6bc52..9fec307 100644 (file)
--- a/sound/core/info.c
+++ b/sound/core/info.c
@@ -606,7 +606,9 @@ int snd_info_get_line(struct snd_info_buffer *buffer, char *line, int len)
 {
        int c;
 
-       if (snd_BUG_ON(!buffer || !buffer->buffer))
+       if (snd_BUG_ON(!buffer))
+               return 1;
+       if (!buffer->buffer)
                return 1;
        if (len <= 0 || buffer->stop || buffer->error)
                return 1;