[PATCH AUTOSEL 5.4 28/84] hibernate: Allow uswsusp to write to swap

[Sasha Levin]

From: Domenico Andreoli <domenico.andreoli@xxxxxxxxx>

[ 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@xxxxxxxxx>
Reported-by: Marian Klein <mkleinsoft@xxxxxxxxx>
Signed-off-by: Domenico Andreoli <domenico.andreoli@xxxxxxxxx>
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 d612468ee66bf..34644ce4b5025 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 {
@@ -1975,7 +1976,8 @@ 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