From patchwork Thu Apr 6 21:51:06 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 13204255 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 80348D533 for ; Thu, 6 Apr 2023 21:51:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0B089C433D2; Thu, 6 Apr 2023 21:51:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1680817892; bh=xMOu0S3bHsnx6eC9qEJCvbZ48iotkfc840hrx9FBaQA=; h=From:To:Cc:Subject:Date:From; b=F6x1ZylpNx5fIKcouBxWHAu5rvRX/0evzMsCdEJIcBgTt0s07WTbT8U7knUQcsSAL juS7r3HHb5EbRq7hZUzMA4dMQtfQ+UjKhlzjYvzFSTuqFMeoLhxww9sS7ccBUhDyR0 ppsl7/tqvckteDkWNykBUoDgsuo0bSFCILeNTYOW53QXtwXKLCwFCQaLcTowdX2luo HhsMNvuLHGao4w+faGBmEYbfvXyku4TMbIu35y4eT7JMya85xjp6TnClEh5PCxZXAS EZozZEXWA5Njoui50lRe7gGHJUOaF2aNxDTWdBDk2NEJIypTlgvM8mQezo0de1gpES Sy2x/7yUtTn7Q== From: Eric Biggers To: fsverity@lists.linux.dev Cc: linux-fsdevel@vger.kernel.org, stable@vger.kernel.org, syzbot+51177e4144d764827c45@syzkaller.appspotmail.com Subject: [PATCH] fsverity: reject FS_IOC_ENABLE_VERITY on mode 3 fds Date: Thu, 6 Apr 2023 14:51:06 -0700 Message-Id: <20230406215106.235829-1-ebiggers@kernel.org> X-Mailer: git-send-email 2.40.0 Precedence: bulk X-Mailing-List: fsverity@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Eric Biggers Commit 56124d6c87fd ("fsverity: support enabling with tree block size < PAGE_SIZE") changed FS_IOC_ENABLE_VERITY to use __kernel_read() to read the file's data, instead of direct pagecache accesses. An unintended consequence of this is that the 'WARN_ON_ONCE(!(file->f_mode & FMODE_READ))' in __kernel_read() became reachable by fuzz tests. This happens if FS_IOC_ENABLE_VERITY is called on a fd opened with access mode 3, which means "ioctl access only". Arguably, FS_IOC_ENABLE_VERITY should work on ioctl-only fds. But ioctl-only fds are a weird Linux extension that is rarely used and that few people even know about. (The documentation for FS_IOC_ENABLE_VERITY even specifically says it requires O_RDONLY.) It's probably not worthwhile to make the ioctl internally open a new fd just to handle this case. Thus, just reject the ioctl on such fds for now. Fixes: 56124d6c87fd ("fsverity: support enabling with tree block size < PAGE_SIZE") Reported-by: syzbot+51177e4144d764827c45@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?id=2281afcbbfa8fdb92f9887479cc0e4180f1c6b28 Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers Reviewed-by: Christoph Hellwig Reviewed-by: Christian Brauner --- fs/verity/enable.c | 7 +++++++ 1 file changed, 7 insertions(+) base-commit: dbd91ed3b5acb7acba2cac2d38e7aec57a5f1e96 diff --git a/fs/verity/enable.c b/fs/verity/enable.c index bbec6f93172cf..fc4c50e5219dc 100644 --- a/fs/verity/enable.c +++ b/fs/verity/enable.c @@ -357,6 +357,13 @@ int fsverity_ioctl_enable(struct file *filp, const void __user *uarg) err = file_permission(filp, MAY_WRITE); if (err) return err; + /* + * __kernel_read() is used while building the Merkle tree. So, we can't + * allow file descriptors that were opened for ioctl access only, using + * the special nonstandard access mode 3. O_RDONLY only, please! + */ + if (!(filp->f_mode & FMODE_READ)) + return -EBADF; if (IS_APPEND(inode)) return -EPERM;