linux-kernel - Re: [PATCH] tmpfs: ensure O_LARGEFILE with generic_file

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Date:   Wed, 28 Sep 2022 23:45:36 +0200
From:   Thomas Weißschuh <linux@...ssschuh.net>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Thomas Weißschuh <thomas.weissschuh@...deus.com>
Subject: Re: [PATCH] tmpfs: ensure O_LARGEFILE with generic_file_open()

On 2022-09-28 13:27-0700, Hugh Dickins wrote:
> From: Hugh Dickins <hughd@...gle.com>
> 
> On Wed, 28 Sep 2022, Thomas Weißschuh wrote:
> > From: Thomas Weißschuh <thomas.weissschuh@...deus.com>
> > 
> > Without this check open() will open large files on tmpfs although
> > O_LARGEFILE was not specified. This is inconsistent with other
> > filesystems.
> > Also it will later result in EOVERFLOW on stat() or EFBIG on write().
> > 
> > Link: https://lore.kernel.org/lkml/76bedae6-22ea-4abc-8c06-b424ceb39217@t-8ch.de/
> > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...deus.com>
> 
> Acked-by: Hugh Dickins <hughd@...gle.com>
> 
> Thanks! I think you deserve some special award for finding and fixing
> such an ancient bug/inconsistency - dating back to early v2.4 it seems.

Seems to be my special talent.

> But only affecting 32-bit; and since we've happily lived with it so long,
> and the fix does change behaviour for userspace, better not to Cc stable.

That was my feeling, too.

> There are some other filesystems still behaving as tmpfs was (ramfs,
> hugetlbfsi, and I didn't look further); but we do make more of an effort
> to keep tmpfs in line with the major filesystems - thank you.

NFS seems also to be affected, which I think warrants a fix.
My plan was to wait for the feedback to this patch and if it works out to then
submit patches for NFS as validating that will be a bit more involved.

> > ---
> >  mm/shmem.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/mm/shmem.c b/mm/shmem.c
> > index 42e5888bf84d..902c5550fabc 100644
> > --- a/mm/shmem.c
> > +++ b/mm/shmem.c
> > @@ -3876,6 +3876,7 @@ EXPORT_SYMBOL(shmem_aops);
> >  
> >  static const struct file_operations shmem_file_operations = {
> >  	.mmap		= shmem_mmap,
> > +	.open		= generic_file_open,
> >  	.get_unmapped_area = shmem_get_unmapped_area,
> >  #ifdef CONFIG_TMPFS
> >  	.llseek		= shmem_file_llseek,
> > 
> > base-commit: f76349cf41451c5c42a99f18a9163377e4b364ff
> > -- 
> > 2.37.3