linux-kernel - [PATCH 5.6 087/166] hibernate: Allow uswsusp to write to swap

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Date:   Wed, 22 Apr 2020 11:56:54 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Domenico Andreoli <domenico.andreoli@...ux.com>,
        Marian Klein <mkleinsoft@...il.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.6 087/166] hibernate: Allow uswsusp to write to swap

From: Domenico Andreoli <domenico.andreoli@...ux.com>

[ Upstream commit 56939e014a6c212b317414faa307029e2e80c3b9 ]

It turns out that there is one use case for programs being able to
write to swap devices, and that is the userspace hibernation code.

Quick fix: disable the S_SWAPFILE check if hibernation is configured.

Fixes: dc617f29dbe5 ("vfs: don't allow writes to swap files")
Reported-by: Domenico Andreoli <domenico.andreoli@...ux.com>
Reported-by: Marian Klein <mkleinsoft@...il.com>
Signed-off-by: Domenico Andreoli <domenico.andreoli@...ux.com>
Reviewed-by: Darrick J. Wong <darrick.wong@...cle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/block_dev.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 69bf2fb6f7cda..84fe0162ff13e 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -34,6 +34,7 @@
 #include <linux/task_io_accounting_ops.h>
 #include <linux/falloc.h>
 #include <linux/uaccess.h>
+#include <linux/suspend.h>
 #include "internal.h"
 
 struct bdev_inode {
@@ -2001,7 +2002,8 @@ ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	if (bdev_read_only(I_BDEV(bd_inode)))
 		return -EPERM;
 
-	if (IS_SWAPFILE(bd_inode))
+	/* uswsusp needs write permission to the swap */
+	if (IS_SWAPFILE(bd_inode) && !hibernation_available())
 		return -ETXTBSY;
 
 	if (!iov_iter_count(from))
-- 
2.20.1