relay: check return of create_buf_file() properly

BugLink: https://bugs.launchpad.net/bugs/1837813
[ Upstream commit 2c1cf00eeacb784781cf1c9896b8af001246d339 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/kernel/relay.c b/kernel/relay.c
index 1537158c67b38e139dc20de59525e738c1f66f21..61d37e6da22dd1c30a7f15f28ec3bdfc5c17f9b0 100644 (file)
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -427,6 +427,8 @@ 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);
 
@@ -460,7 +462,7 @@ 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;
        }