Re: [PATCH] mm/filemap: Fix NULL pointer dereference in pagecache_get_page

[Andrew Morton]

On Tue, 26 Apr 2022 13:08:08 +0100 Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:

> On Tue, Apr 26, 2022 at 04:25:48PM +0800, Wan Jiabing wrote:
> > Fix following coccicheck error:
> > mm/folio-compat.c:128:17-21: ERROR: folio is NULL but dereferenced.
> >  	folio = __filemap_get_folio(mapping, index, fgp_flags, gfp);
> > -	if ((fgp_flags & FGP_HEAD) || !folio || xa_is_value(folio))
> > +	if (!folio)
> > +		return NULL;
> > +	if ((fgp_flags & FGP_HEAD) || xa_is_value(folio))
> >  		return &folio->page;
> 
> That doesn't dereference the folio.  Coccicheck is wrong.

Doing

		return &(0->page);

is a rather obscure way of doing `return NULL;'.

I agree the patch doesn't fix anything, but it results in saner-looking code?