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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Kees Cook <keescook@chromium.org>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Rientjes <rientjes@google.com>,
        Sasha Levin <sashal@kernel.org>,
        syzbot+16c3a70e1e9b29346c43@syzkaller.appspotmail.com
Subject: [PATCH 4.14 100/135] relay: check return of create_buf_file() properly
Date:   Tue, 12 Mar 2019 10:09:07 -0700
Message-Id: <20190312170350.394798703@linuxfoundation.org>
In-Reply-To: <20190312170341.127810985@linuxfoundation.org>
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4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

[ 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>
---
 kernel/relay.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/relay.c b/kernel/relay.c
index 1537158c67b3..61d37e6da22d 100644
--- 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;
 	}
 
-- 
2.19.1