nfs: prevent truncate on active swapfile

Most filesystems prevent truncation of an active swapfile by way of
inode_newsize_ok, called from inode_change_ok. NFS doesn't call either
from nfs_setattr, presumably because most of these checks are expected
to be done server-side. However, the IS_SWAPFILE check can only be done
client-side, and truncating a swapfile can't possibly be good.

Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 2211f6ba8736..d2398c193bda 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -507,10 +507,15 @@ nfs_setattr(struct dentry *dentry, struct iattr *attr)
                 attr->ia_valid &= ~ATTR_MODE;
 
         if (attr->ia_valid & ATTR_SIZE) {
+                loff_t i_size;
+
                 BUG_ON(!S_ISREG(inode->i_mode));
 
-                if (attr->ia_size == i_size_read(inode))
+                i_size = i_size_read(inode);
+                if (attr->ia_size == i_size)
                         attr->ia_valid &= ~ATTR_SIZE;
+                else if (attr->ia_size < i_size && IS_SWAPFILE(inode))
+                        return -ETXTBSY;
         }
 
         /* Optimization: if the end result is no change, don't RPC */