linux-kernel - Re: [PATCH v4] proc: report open files as size in stat() for /proc/pid/fd

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Date:   Fri, 18 Nov 2022 14:33:27 -0500
From:   Brian Foster <bfoster@...hat.com>
To:     Ivan Babrou <ivan@...udflare.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...udflare.com, Alexey Dobriyan <adobriyan@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Theodore Ts'o <tytso@....edu>,
        David Laight <David.Laight@...lab.com>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Christoph Anton Mitterer <mail@...istoph.anton.mitterer.name>,
        Mike Rapoport <rppt@...nel.org>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH v4] proc: report open files as size in stat() for
 /proc/pid/fd

On Fri, Nov 18, 2022 at 11:18:36AM -0800, Ivan Babrou wrote:
> On Fri, Nov 18, 2022 at 11:10 AM Brian Foster <bfoster@...hat.com> wrote:
> > > +static int proc_fd_getattr(struct user_namespace *mnt_userns,
> > > +                     const struct path *path, struct kstat *stat,
> > > +                     u32 request_mask, unsigned int query_flags)
> > > +{
> > > +     struct inode *inode = d_inode(path->dentry);
> > > +     int rv = 0;
> > > +
> > > +     generic_fillattr(&init_user_ns, inode, stat);
> > > +
> >
> > Sorry I missed this on v3, but shouldn't this pass through the
> > mnt_userns parameter?
> 
> The mnt_userns parameter was added in 549c729 (fs: make helpers idmap
> mount aware), and it's not passed anywhere in fs/proc.
> 
> Looking at other uses of generic_fillattr, all of them use "init_user_ns":
> 

Interesting. It looks like this would have used mnt_userns from
vfs_getattr_nosec() before proc_fd_getattr() is wired up, right? I'm not
familiar enough with that change to say whether /proc should use one
value or the other, or perhaps it just doesn't matter.?

Christian?

Brian

> $ rg generic_fillattr fs/proc
> fs/proc/proc_net.c
> 301: generic_fillattr(&init_user_ns, inode, stat);
> 
> fs/proc/base.c
> 1970: generic_fillattr(&init_user_ns, inode, stat);
> 3856: generic_fillattr(&init_user_ns, inode, stat);
> 
> fs/proc/root.c
> 315: generic_fillattr(&init_user_ns, d_inode(path->dentry), stat);
> 
> fs/proc/generic.c
> 150: generic_fillattr(&init_user_ns, inode, stat);
> 
> fs/proc/proc_sysctl.c
> 841: generic_fillattr(&init_user_ns, inode, stat);
>