linux-kernel - [PATCH 1/2] mm: set S_SWAPFILE on blockdev swap devices

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Date:   Fri, 28 Jun 2019 11:35:17 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     hch@...radead.org, akpm@...ux-foundation.org, tytso@....edu,
        viro@...iv.linux.org.uk, darrick.wong@...cle.com
Cc:     linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 1/2] mm: set S_SWAPFILE on blockdev swap devices

From: Darrick J. Wong <darrick.wong@...cle.com>

Set S_SWAPFILE on block device inodes so that they have the same
protections as a swap flie.

Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
---
 mm/swapfile.c |   31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)


diff --git a/mm/swapfile.c b/mm/swapfile.c
index 596ac98051c5..fa4edd0cca3a 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2284,9 +2284,8 @@ EXPORT_SYMBOL_GPL(add_swap_extent);
  * requirements, they are simply tossed out - we will never use those blocks
  * for swapping.
  *
- * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
- * prevents root from shooting her foot off by ftruncating an in-use swapfile,
- * which will scribble on the fs.
+ * For all swap devices we set S_SWAPFILE across the life of the swapon.  This
+ * prevents users from writing to the swap device, which will corrupt memory.
  *
  * The amount of disk space which a single swap extent represents varies.
  * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
@@ -2551,13 +2550,14 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	inode = mapping->host;
 	if (S_ISBLK(inode->i_mode)) {
 		struct block_device *bdev = I_BDEV(inode);
+
 		set_blocksize(bdev, old_block_size);
 		blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
-	} else {
-		inode_lock(inode);
-		inode->i_flags &= ~S_SWAPFILE;
-		inode_unlock(inode);
 	}
+
+	inode_lock(inode);
+	inode->i_flags &= ~S_SWAPFILE;
+	inode_unlock(inode);
 	filp_close(swap_file, NULL);
 
 	/*
@@ -2780,11 +2780,11 @@ static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
 		p->flags |= SWP_BLKDEV;
 	} else if (S_ISREG(inode->i_mode)) {
 		p->bdev = inode->i_sb->s_bdev;
-		inode_lock(inode);
-		if (IS_SWAPFILE(inode))
-			return -EBUSY;
-	} else
-		return -EINVAL;
+	}
+
+	inode_lock(inode);
+	if (IS_SWAPFILE(inode))
+		return -EBUSY;
 
 	return 0;
 }
@@ -3185,8 +3185,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	atomic_inc(&proc_poll_event);
 	wake_up_interruptible(&proc_poll_wait);
 
-	if (S_ISREG(inode->i_mode))
-		inode->i_flags |= S_SWAPFILE;
+	inode->i_flags |= S_SWAPFILE;
 	error = 0;
 	goto out;
 bad_swap:
@@ -3208,7 +3207,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	if (inced_nr_rotate_swap)
 		atomic_dec(&nr_rotate_swap);
 	if (swap_file) {
-		if (inode && S_ISREG(inode->i_mode)) {
+		if (inode) {
 			inode_unlock(inode);
 			inode = NULL;
 		}
@@ -3221,7 +3220,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	}
 	if (name)
 		putname(name);
-	if (inode && S_ISREG(inode->i_mode))
+	if (inode)
 		inode_unlock(inode);
 	if (!error)
 		enable_swap_slots_cache();