Re: [f2fs-dev] [PATCH] f2fs: reject setattr writes on large folio files

[Wenjie Qi]

Updated in v2 by dropping the obsolete user.fadvise/chmod case and
restricting the fix
 to ATTR_SIZE on immutable large-folio mappings.
https://lore.kernel.org/linux-f2fs-devel/20260610143735.3169935-1-qiwenjie@xxxxxxxxxx/T/#u

On Wed, Jun 10, 2026 at 8:26 AM Jaegeuk Kim <jaegeuk@xxxxxxxxxx> wrote:
>
> On 05/21, Wenjie Qi wrote:
> > F2FS large folio support is read-only. It rejects writable opens and
> > mmap writes when an inode mapping supports large folios, but setattr can
> > still reach the inode without going through those checks.
> >
> > For immutable large-folio files, clearing the immutable flag keeps the
> > cached inode and its large-folio mapping alive until the inode is
> > dropped. A path-based truncate(2) can then call f2fs_setattr() with
> > ATTR_SIZE and change the file size without opening the file for write.
> >
> > The user.fadvise path adds another visible case: after the file is
> > reopened with large folios, chmod(WRITE) is documented to fail, but
> > f2fs_setattr() currently allows ATTR_MODE to add write bits back.
>
> We don't add this anymore. Can you update?
>
> >
> > Reject size changes and mode changes that enable write permissions while
> > the mapping still supports large folios. Read-only mode changes and
> > unrelated metadata updates remain allowed.
> >
> > Fixes: 05e65c14ea59 ("f2fs: support large folio for immutable non-compressed case")
> > Signed-off-by: Wenjie Qi <qiwenjie@xxxxxxxxxx>
> > ---
> >  fs/f2fs/file.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > index 71385ca4163d..3880ff5e6740 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -1097,6 +1097,11 @@ int f2fs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
> >                                 ATTR_GID | ATTR_TIMES_SET))))
> >               return -EPERM;
> >
> > +     if (mapping_large_folio_support(inode->i_mapping) &&
> > +         ((attr->ia_valid & ATTR_SIZE) ||
> > +          ((attr->ia_valid & ATTR_MODE) && (attr->ia_mode & 0222))))
> > +             return -EOPNOTSUPP;
> > +
> >       if ((attr->ia_valid & ATTR_SIZE)) {
> >               if (!f2fs_is_compress_backend_ready(inode) ||
> >                               IS_DEVICE_ALIASING(inode))
> > --
> > 2.43.0
> >
> >
> >
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