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>

1 files changed, 3 insertions, 0 deletions

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;