linux-ext4 - Re: [PATCH v5 22/42] open: handle idmapped mounts in do

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Message-ID: <20210119093720.GG3364550@infradead.org>
Date:   Tue, 19 Jan 2021 09:37:20 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org,
        John Johansen <john.johansen@...onical.com>,
        James Morris <jmorris@...ei.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Geoffrey Thomas <geofft@...reload.com>,
        Mrunal Patel <mpatel@...hat.com>,
        Josh Triplett <josh@...htriplett.org>,
        Andy Lutomirski <luto@...nel.org>,
        Theodore Tso <tytso@....edu>, Alban Crequy <alban@...volk.io>,
        Tycho Andersen <tycho@...ho.ws>,
        David Howells <dhowells@...hat.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Seth Forshee <seth.forshee@...onical.com>,
        St??phane Graber <stgraber@...ntu.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Lennart Poettering <lennart@...ttering.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, smbarber@...omium.org,
        Phil Estes <estesp@...il.com>, Serge Hallyn <serge@...lyn.com>,
        Kees Cook <keescook@...omium.org>,
        Todd Kjos <tkjos@...gle.com>, Paul Moore <paul@...l-moore.com>,
        Jonathan Corbet <corbet@....net>,
        containers@...ts.linux-foundation.org,
        linux-security-module@...r.kernel.org, linux-api@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-integrity@...r.kernel.org, selinux@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v5 22/42] open: handle idmapped mounts in do_truncate()

On Tue, Jan 12, 2021 at 11:01:04PM +0100, Christian Brauner wrote:
> @@ -930,8 +932,12 @@ void dump_truncate(struct coredump_params *cprm)
>  
>  	if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
>  		offset = file->f_op->llseek(file, 0, SEEK_CUR);
> -		if (i_size_read(file->f_mapping->host) < offset)
> -			do_truncate(file->f_path.dentry, offset, 0, file);
> +		if (i_size_read(file->f_mapping->host) < offset) {
> +			struct user_namespace *mnt_userns;
> +
> +			mnt_userns = file_user_ns(file);
> +			do_truncate(mnt_userns, file->f_path.dentry, offset, 0, file);
> +		}

I think we can skip the local variable here.  In fact for all callers
of do_truncate except vfs_truncate a little file_truncate helper that
takes a struct file would help readability a lot.