mm: do not access page->mapping directly on page_endio

commit dd8416c47715cf324c9a16f13273f9fda87acfed upstream.

With rw_page, page_endio is used for completing IO on a page and it
propagates write error to the address space if the IO fails.  The
problem is it accesses page->mapping directly which might be okay for
file-backed pages but it shouldn't for anonymous page.  Otherwise, it
can corrupt one of field from anon_vma under us and system goes panic
randomly.

swap_writepage
  bdev_writepage
    ops->rw_page

I encountered the BUG during developing new zram feature and it was
really hard to figure it out because it made random crash, somtime
mmap_sem lockdep, sometime other places where places never related to
zram/zsmalloc, and not reproducible with some configuration.

When I consider how that bug is subtle and people do fast-swap test with
brd, it's worth to add stable mark, I think.

Fixes: dd6bd0d9c7db ("swap: use bdev_read_page() / bdev_write_page()")
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index d8d7df82c69a..edfb90e3830c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -910,9 +910,12 @@ void page_endio(struct page *page, bool is_write, int err)
                 unlock_page(page);
         } else {
                 if (err) {
+                        struct address_space *mapping;
+
                         SetPageError(page);
-                        if (page->mapping)
-                                mapping_set_error(page->mapping, err);
+                        mapping = page_mapping(page);
+                        if (mapping)
+                                mapping_set_error(mapping, err);
                 }
                 end_page_writeback(page);
         }