relay: check return of create_buf_file() properly

If create_buf_file() returns an error, don't try to reference it later
as a valid dentry pointer.

This problem was exposed when debugfs started to return errors instead
of just NULL for some calls when they do not succeed properly.

Also, the check for WARN_ON(dentry) was just wrong :)

Reported-by: Kees Cook <keescook@chromium.org>
Reported-and-tested-by: syzbot+16c3a70e1e9b29346c43@syzkaller.appspotmail.com
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Rientjes <rientjes@google.com>
Fixes: ff9fb72bc077 ("debugfs: return error values, not NULL")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/relay.c b/kernel/relay.c
index 04f248644e065f601d78744be2bbe580a6aa1810..9e0f52375487d7be47ee4c265ee0cbd5227186d0 100644 (file)
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -428,6 +428,8 @@ static struct dentry *relay_create_buf_file(struct rchan *chan,
        dentry = chan->cb->create_buf_file(tmpname, chan->parent,
                                           S_IRUSR, buf,
                                           &chan->is_global);
+       if (IS_ERR(dentry))
+               dentry = NULL;
 
        kfree(tmpname);
 
@@ -461,7 +463,7 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
                dentry = chan->cb->create_buf_file(NULL, NULL,
                                                   S_IRUSR, buf,
                                                   &chan->is_global);
-               if (WARN_ON(dentry))
+               if (IS_ERR_OR_NULL(dentry))
                        goto free_buf;
        }