linux-kernel - Re: [PATCH V5] loop: Add sanity check for read/write

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Message-ID:
 <BL1PR11MB5979EFA72DA54AB231D408CF869FA@BL1PR11MB5979.namprd11.prod.outlook.com>
Date: Tue, 20 May 2025 12:27:44 +0000
From: "Xu, Lizhi" <Lizhi.Xu@...driver.com>
To: "hch@...radead.org" <hch@...radead.org>
CC: Christian Hesse <mail@...rm.de>, "axboe@...nel.dk" <axboe@...nel.dk>,
        "christian@...sel.eu" <christian@...sel.eu>,
        "linux-block@...r.kernel.org"
	<linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        "ming.lei@...hat.com" <ming.lei@...hat.com>,
        "syzbot+6af973a3b8dfd2faefdc@...kaller.appspotmail.com"
	<syzbot+6af973a3b8dfd2faefdc@...kaller.appspotmail.com>,
        "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH V5] loop: Add sanity check for read/write_iter

> isofs does support read_iter, without that it would not have worked
> before either. That is not the problem.  It must be related to
> the FMODE_WRITE check - i.e. we have a writable FD here, but a file
> system that does not actually supports writes.  Which honestly feels
> weird, but we'll have to figure it out to unbreak these setups.
If it is a directory, isofs_dir_operations is used. In this case,
isofs does not support read_iter (I used a directory when testing).
If it is a regular file, generic_ro_fops is used. In this case,
isofs supports read_iter. When a regular file has a writable attribute,
the problem will recur because isofs does not support write_iter.