[PATCH STABLE 4.14 4.19] swap: fix swapfile page to sector mapping

[Anthony Iliopoulos]

commit caf6912f3f4af7232340d500a4a2008f81b93f14 upstream.

Fix block device sector offset calculation for swap page io on top of
blockdevs that provide a rw_page operation and do page-sized io directly
(without the block layer).

Currently swap_page_sector() maps a swap page into a blockdev sector by
obtaining the swap page offset (swap map slot), but ignores the swapfile
starting offset into the blockdev.

In setups where swapfiles are sitting on top of a filesystem, this
results into swapping out activity potentially overwriting filesystem
blocks that fall outside the swapfile region.

[This issue only affects swapfiles on filesystems on top of blockdevs
that implement rw_page ops (brd, zram, btt, pmem), and not on top of any
other block devices, in contrast to the upstream commit fix.]

Fixes: dd6bd0d9c7db ("swap: use bdev_read_page() / bdev_write_page()")
Cc: sta...@vger.kernel.org # 4.14 4.19

Signed-off-by: Anthony Iliopoulos <ail...@suse.com>
---
 mm/page_io.c  | 11 +++--------
 mm/swapfile.c |  2 +-
 2 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index 08d2eae58fce..9b646f07f47f 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -38,7 +38,6 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
 
                bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
                bio_set_dev(bio, bdev);
-               bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
                bio->bi_end_io = end_io;
 
                for (i = 0; i < nr; i++)
@@ -262,11 +261,6 @@ int swap_writepage(struct page *page, struct 
writeback_control *wbc)
        return ret;
 }
 
-static sector_t swap_page_sector(struct page *page)
-{
-       return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9);
-}
-
 static inline void count_swpout_vm_event(struct page *page)
 {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
@@ -325,7 +319,8 @@ int __swap_writepage(struct page *page, struct 
writeback_control *wbc,
                return ret;
        }
 
-       ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc);
+       ret = bdev_write_page(sis->bdev, map_swap_page(page, &sis->bdev),
+                             page, wbc);
        if (!ret) {
                count_swpout_vm_event(page);
                return 0;
@@ -376,7 +371,7 @@ int swap_readpage(struct page *page, bool synchronous)
                return ret;
        }
 
-       ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
+       ret = bdev_read_page(sis->bdev, map_swap_page(page, &sis->bdev), page);
        if (!ret) {
                if (trylock_page(page)) {
                        swap_slot_free_notify(page);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 130e2e41a48c..057e6907bf7b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2305,7 +2305,7 @@ sector_t map_swap_page(struct page *page, struct 
block_device **bdev)
 {
        swp_entry_t entry;
        entry.val = page_private(page);
-       return map_swap_entry(entry, bdev);
+       return map_swap_entry(entry, bdev) << (PAGE_SHIFT - 9);
 }
 
 /*
-- 
2.30.1