linux-kernel - Re: [PATCH] mm/secretmem: fix panic when growing a memfd

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Date:   Mon, 11 Apr 2022 10:29:31 -0700
From:   Axel Rasmussen <axelrasmussen@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Mike Rapoport <rppt@...nel.org>, Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org
Subject: Re: [PATCH] mm/secretmem: fix panic when growing a memfd_secret

It's a reasonable option.

Worth noting though that today when it says "larger than the maximum
file size", it refers to the global MAX_NON_LFS (2^31), not
necessarily growing in general. So, we're extending the meaning a bit.

But, I'm happy to send a v2 with EINVAL instead.


On Thu, Apr 7, 2022 at 1:50 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Thu, 31 Mar 2022 10:42:12 -0700 Axel Rasmussen <axelrasmussen@...gle.com> wrote:
>
> > Any strong opinions on which error code is used? I think overall I
> > would still pick EOPNOTSUPP, but happy to change it if anyone feels
> > strongly.
> >
> > - I think ENOSYS is specific to syscall nr not defined
> > - I think ENOTTY is specific to ioctls
> > - The kernel (sort of mistakenly) defines ENOTSUPP instead of ENOTSUP,
> > but it's marked deprecated and it's recommended to use EOPNOTSUPP
> > instead (despite POSIX saying these should be distinct and for
> > different uses).
>
> `man ftruncate' sayeth
>
>        EINVAL The argument length is negative or larger than the maximum  file
>               size.
>
> which reasonably accurately describes what we're doing here?
>
> +       if ((ia_valid & ATTR_SIZE) && inode->i_size)
> +               return -EOPNOTSUPP;
>
>