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>

6 files changed, 38 insertions, 3 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index c2a85b587922..d9bab63a9b81 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1978,6 +1978,9 @@ 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 56b8e358af5c..a2e3d446ba8e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3547,4 +3547,15 @@ 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 d0cf700bf201..40667c2f3383 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2988,6 +2988,9 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
         loff_t count;
         int ret;
 
+        if (IS_SWAPFILE(inode))
+                return -ETXTBSY;
+
         if (!iov_iter_count(from))
                 return 0;
 
diff --git a/mm/memory.c b/mm/memory.c
index e2bb51b6242e..b1dff75640b7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2196,6 +2196,10 @@ static vm_fault_t 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 7e8c3e8ae75f..6bc21fca20bc 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1483,8 +1483,12 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
                 case MAP_SHARED_VALIDATE:
                         if (flags & ~flags_mask)
                                 return -EOPNOTSUPP;
-                        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 a53b7c49b40e..dab43523afdd 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3275,6 +3275,17 @@ 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)
@@ -3295,7 +3306,6 @@ 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: