[PATCH 5/5] 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/attr.c     |    3 +++
 mm/filemap.c  |    3 +++
 mm/memory.c   |    4 +++-
 mm/mmap.c     |    2 ++
 mm/swapfile.c |   15 +++++++++++++--
 5 files changed, 24 insertions(+), 3 deletions(-)


diff --git a/fs/attr.c b/fs/attr.c
index 1fcfdcc5b367..42f4d4fb0631 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -236,6 +236,9 @@ int notify_change(struct dentry * dentry, struct iattr * 
attr, struct inode **de
        if (IS_IMMUTABLE(inode))
                return -EPERM;
 
+       if (IS_SWAPFILE(inode))
+               return -ETXTBSY;
+
        if ((ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) &&
            IS_APPEND(inode))
                return -EPERM;
diff --git a/mm/filemap.c b/mm/filemap.c
index dad85e10f5f8..fd80bc20e30a 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2938,6 +2938,9 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, 
struct iov_iter *from)
        if (IS_IMMUTABLE(inode))
                return -EPERM;
 
+       if (IS_SWAPFILE(inode))
+               return -ETXTBSY;
+
        if (!iov_iter_count(from))
                return 0;
 
diff --git a/mm/memory.c b/mm/memory.c
index 4311cfdade90..c04c6a689995 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2235,7 +2235,9 @@ 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_IMMUTABLE(file_inode(vmf->vma->vm_file)))
+       if (vmf->vma->vm_file &&
+           (IS_IMMUTABLE(file_inode(vmf->vma->vm_file)) ||
+            IS_SWAPFILE(file_inode(vmf->vma->vm_file))))
                return VM_FAULT_SIGBUS;
 
        ret = vmf->vma->vm_ops->page_mkwrite(vmf);
diff --git a/mm/mmap.c b/mm/mmap.c
index ac1e32205237..031807339869 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1488,6 +1488,8 @@ unsigned long do_mmap(struct file *file, unsigned long 
addr,
                                        return -EACCES;
                                if (IS_IMMUTABLE(file_inode(file)))
                                        return -EPERM;
+                               if (IS_SWAPFILE(file_inode(file)))
+                                       return -ETXTBSY;
                        }
 
                        /*
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 596ac98051c5..1ca4ee8c2d60 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3165,6 +3165,19 @@ 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 file.
+        */
+       if (S_ISREG(inode->i_mode)) {
+               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)
@@ -3185,8 +3198,6 @@ 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;
        error = 0;
        goto out;
 bad_swap: