[PATCH 2/2] vfs: don't allow writes to swap files

[Darrick J. Wong]

From: Darrick J. Wong <darrick.w...@oracle.com>

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.w...@oracle.com>
---
 fs/block_dev.c |    3 +++
 mm/filemap.c   |    3 +++
 mm/memory.c    |    4 ++++
 mm/mmap.c      |    8 ++++++--
 mm/swapfile.c  |   12 +++++++++++-
 5 files changed, 27 insertions(+), 3 deletions(-)


diff --git a/fs/block_dev.c b/fs/block_dev.c
index eb657ab94060..017f46719ebe 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -2011,6 +2011,9 @@ 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/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: