linux-kernel - Re: [GIT PULL] pidfd updates

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Date:   Thu, 27 Apr 2023 10:11:40 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] pidfd updates

On Thu, Apr 27, 2023 at 02:07:15AM +0100, Al Viro wrote:
> On Tue, Apr 25, 2023 at 02:34:15PM +0200, Christian Brauner wrote:
> 
> 
> > struct fd_file {
> > 	struct file *file;
> > 	int fd;
> > 	int __user *fd_user;
> 
> Why is it an int?  Because your case has it that way?
> 
> We have a bunch of places where we have an ioctl with
> a field in some structure filled that way; any primitive
> that combines put_user() with descriptor handling is
> going to cause trouble as soon as somebody deals with
> a structure where such member is unsigned long.  Gets
> especially funny on 64bit big-endian...
> 
> And that objection is orthogonal to that 3-member structure -
> even if you pass int __user * as an explicit argument into
> your helper, the same trouble will be there.

Ignoring for a second that there are other ways to achieve this. This is
literally the sketch on top of a sketch to encompass an api that _we do
already have today_...