From f1a7f58cf4d55a1f398f7d4e59c86fad5869b454 Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <darrick.wong@oracle.com>
Date: Tue, 20 Aug 2019 07:55:16 -0700
Subject: [PATCH] vfs: don't allow writes to swap files

Don't let userspace write to an active swap file because the kernel
effectively has a long term lease on the storage and things could get
seriously corrupted if we let this happen.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/block_dev.c     |  3 +++
 include/linux/fs.h | 11 +++++++++++
 mm/filemap.c       |  3 +++
 mm/memory.c        |  4 ++++
 mm/mmap.c          |  8 ++++++--
 mm/swapfile.c      | 12 +++++++++++-
 6 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 789f55e851ae..f408ebc5bd66 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1890,6 +1890,9 @@ 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))
+		return -ETXTBSY;
+
 	if (!iov_iter_count(from))
 		return 0;
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0988d705960c..d07269956030 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3420,4 +3420,15 @@ static inline void simple_fill_fsxattr(struct fsxattr *fa, __u32 xflags)
 	fa->fsx_xflags = xflags;
 }
 
+/*
+ * Flush file data before changing attributes.  Caller must hold any locks
+ * required to prevent further writes to this file until we're done setting
+ * flags.
+ */
+static inline int inode_drain_writes(struct inode *inode)
+{
+	inode_dio_wait(inode);
+	return filemap_write_and_wait(inode->i_mapping);
+}
+
 #endif /* _LINUX_FS_H */
diff --git a/mm/filemap.c b/mm/filemap.c
index 6eb4e32d99c8..f370f94e8ad1 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2828,6 +2828,9 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
 	unsigned long limit = rlimit(RLIMIT_FSIZE);
 	loff_t pos;
 
+	if (IS_SWAPFILE(inode))
+		return -ETXTBSY;
+
 	if (!iov_iter_count(from))
 		return 0;
 
diff --git a/mm/memory.c b/mm/memory.c
index a728bed16c20..1a1da025e5ee 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2350,6 +2350,10 @@ static int do_page_mkwrite(struct vm_fault *vmf)
 
 	vmf->flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
 
+	if (vmf->vma->vm_file &&
+	    IS_SWAPFILE(vmf->vma->vm_file->f_mapping->host))
+		return VM_FAULT_SIGBUS;
+
 	ret = vmf->vma->vm_ops->page_mkwrite(vmf);
 	/* Restore original flags so that caller is not surprised */
 	vmf->flags = old_flags;
diff --git a/mm/mmap.c b/mm/mmap.c
index 476e810cf100..8d596bfb792f 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1390,8 +1390,12 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 
 		switch (flags & MAP_TYPE) {
 		case MAP_SHARED:
-			if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE))
-				return -EACCES;
+			if (prot & PROT_WRITE) {
+				if (!(file->f_mode & FMODE_WRITE))
+					return -EACCES;
+				if (IS_SWAPFILE(file->f_mapping->host))
+					return -ETXTBSY;
+			}
 
 			/*
 			 * Make sure we don't allow writing to an append-only
diff --git a/mm/swapfile.c b/mm/swapfile.c
index be677a8a2691..2f68455f7d55 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3253,6 +3253,17 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	if (error)
 		goto bad_swap;
 
+	/*
+	 * Flush any pending IO and dirty mappings before we start using this
+	 * swap device.
+	 */
+	inode->i_flags |= S_SWAPFILE;
+	error = inode_drain_writes(inode);
+	if (error) {
+		inode->i_flags &= ~S_SWAPFILE;
+		goto bad_swap;
+	}
+
 	mutex_lock(&swapon_mutex);
 	prio = -1;
 	if (swap_flags & SWAP_FLAG_PREFER)
@@ -3273,7 +3284,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	atomic_inc(&proc_poll_event);
 	wake_up_interruptible(&proc_poll_wait);
 
-	inode->i_flags |= S_SWAPFILE;
 	error = 0;
 	goto out;
 bad_swap: