linux-kernel - [PATCH 4.4 29/30] swap: fix swapfile read/write offset

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Message-Id: <20210305120850.860813577@linuxfoundation.org>
Date:   Fri,  5 Mar 2021 13:22:58 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Anthony Iliopoulos <ailiop@...e.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 4.4 29/30] swap: fix swapfile read/write offset

From: Jens Axboe <axboe@...nel.dk>

commit caf6912f3f4af7232340d500a4a2008f81b93f14 upstream.

We're not factoring in the start of the file for where to write and
read the swapfile, which leads to very unfortunate side effects of
writing where we should not be...

[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: stable@...r.kernel.org # 4.4
Signed-off-by: Anthony Iliopoulos <ailiop@...e.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/page_io.c  |   11 +++--------
 mm/swapfile.c |    2 +-
 2 files changed, 4 insertions(+), 9 deletions(-)

--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -32,7 +32,6 @@ static struct bio *get_swap_bio(gfp_t gf
 	bio = bio_alloc(gfp_flags, 1);
 	if (bio) {
 		bio->bi_iter.bi_sector = map_swap_page(page, &bio->bi_bdev);
-		bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
 		bio->bi_end_io = end_io;
 
 		bio_add_page(bio, page, PAGE_SIZE, 0);
@@ -244,11 +243,6 @@ out:
 	return ret;
 }
 
-static sector_t swap_page_sector(struct page *page)
-{
-	return (sector_t)__page_file_index(page) << (PAGE_CACHE_SHIFT - 9);
-}
-
 int __swap_writepage(struct page *page, struct writeback_control *wbc,
 		bio_end_io_t end_write_func)
 {
@@ -297,7 +291,8 @@ int __swap_writepage(struct page *page,
 		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_vm_event(PSWPOUT);
 		return 0;
@@ -345,7 +340,7 @@ int swap_readpage(struct page *page)
 		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) {
 		count_vm_event(PSWPIN);
 		return 0;
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1653,7 +1653,7 @@ sector_t map_swap_page(struct page *page
 {
 	swp_entry_t entry;
 	entry.val = page_private(page);
-	return map_swap_entry(entry, bdev);
+	return map_swap_entry(entry, bdev) << (PAGE_SHIFT - 9);
 }
 
 /*