On Mon, 30 Sep 2024 11:02:26 +0200 Gianfranco Trad <gianf.trad@xxxxxxxxx> wrote: > Add check on filler to prevent NULL pointer dereference condition in > read_cache_folio[1]. > > [1] https://syzkaller.appspot.com/bug?extid=4089e577072948ac5531 Test case https://syzkaller.appspot.com/x/repro.c?x=10a0d880580000 > diff --git a/mm/filemap.c b/mm/filemap.c > index 4f3753f0a158..88de8029133c 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2360,6 +2360,8 @@ static int filemap_read_folio(struct file *file, filler_t filler, > /* Start the actual read. The read will unlock the page. */ > if (unlikely(workingset)) > psi_memstall_enter(&pflags); > + if (!filler) > + return -EIO; > error = filler(file, folio); > if (unlikely(workingset)) > psi_memstall_leave(&pflags); do_read_cache_folio() already handles a NULL filler (from freader_get_folio()'s read_cache_folio() call). if (!filler) filler = mapping->a_ops->read_folio; so I'm suspecting that an appropriate fix is to teach the underlying address_space_operations (appears to be from /proc/pid/maps) to implement ->read_folio().
