[PATCH 7/7] vfs: don't allow writes to swap files

Darrick J. Wong
2019-06-22T00:00:28Z

From: Darrick J. Wong <darrick.wong@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.wong@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..390859785558 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_flush_data(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;