linux-kernel - Re: [regression, bisected] Bug 216738 - Adding O_APPEND to O_RDWR with fcntl(fd, F

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Date:   Thu, 24 Nov 2022 21:33:54 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Thorsten Leemhuis <regressions@...mhuis.info>,
        Linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>,
        LKML <linux-kernel@...r.kernel.org>,
        "Christian Brauner (Microsoft)" <brauner@...nel.org>,
        Pierre Labastie <pierre.labastie@...f.fr>,
        linux-unionfs@...r.kernel.org
Subject: Re: [regression, bisected] Bug 216738 - Adding O_APPEND to O_RDWR
 with fcntl(fd, F_SETFL) does not work on overlayfs

On Thu, 24 Nov 2022 at 18:03, Al Viro <viro@...iv.linux.org.uk> wrote:

> So basically we have this
> static int ovl_change_flags(struct file *file, unsigned int flags)
> {
>         struct inode *inode = file_inode(file);
>         int err;
>
>         flags &= OVL_SETFL_MASK;
>
>         if (((flags ^ file->f_flags) & O_APPEND) && IS_APPEND(inode))
>                 return -EPERM;
>
>         if ((flags & O_DIRECT) && !(file->f_mode & FMODE_CAN_ODIRECT))
>                 return -EINVAL;
>
>         if (file->f_op->check_flags) {
>                 err = file->f_op->check_flags(flags);
>                 if (err)
>                         return err;
>         }
>
>         spin_lock(&file->f_lock);
>         file->f_flags = (file->f_flags & ~OVL_SETFL_MASK) | flags;
>         spin_unlock(&file->f_lock);
>
>         return 0;
> }
> open-coding what setfl() would've done, without updating ->f_iocb_flags...
> Not hard to deal with...
>
> I could pick it in vfs.git #fixes, or Miklos could put it through his tree.
> Miklos, which way would you prefer that to go?

I'll pick this into #overlayfs-next, as a PR for this cycle is needed anyway.

Thanks,
Miklos