ovl: copy up sync/noatime fileattr flags

When a lower file has sync/noatime fileattr flags, the behavior of
overlayfs post copy up is inconsistent.

Immediately after copy up, ovl inode still has the S_SYNC/S_NOATIME
inode flags copied from lower inode, so vfs code still treats the ovl
inode as sync/noatime.  After ovl inode evict or mount cycle,
the ovl inode does not have these inode flags anymore.

To fix this inconsistency, try to copy the fileattr flags on copy up
if the upper fs supports the fileattr_set() method.

This gives consistent behavior post copy up regardless of inode eviction
from cache.

We cannot copy up the immutable/append-only inode flags in a similar
manner, because immutable/append-only inodes cannot be linked and because
overlayfs will not be able to set overlay.* xattr on the upper inodes.

Those flags will be addressed by a followup patch.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 31 insertions, 13 deletions

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 5e828a1c98a8..b288843e6b42 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -503,16 +503,14 @@ static int ovl_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
  * Introducing security_inode_fileattr_get/set() hooks would solve this issue
  * properly.
  */
-static int ovl_security_fileattr(struct dentry *dentry, struct fileattr *fa,
+static int ovl_security_fileattr(struct path *realpath, struct fileattr *fa,
 				 bool set)
 {
-	struct path realpath;
 	struct file *file;
 	unsigned int cmd;
 	int err;
 
-	ovl_path_real(dentry, &realpath);
-	file = dentry_open(&realpath, O_RDONLY, current_cred());
+	file = dentry_open(realpath, O_RDONLY, current_cred());
 	if (IS_ERR(file))
 		return PTR_ERR(file);
 
@@ -527,11 +525,22 @@ static int ovl_security_fileattr(struct dentry *dentry, struct fileattr *fa,
 	return err;
 }
 
+int ovl_real_fileattr_set(struct path *realpath, struct fileattr *fa)
+{
+	int err;
+
+	err = ovl_security_fileattr(realpath, fa, true);
+	if (err)
+		return err;
+
+	return vfs_fileattr_set(&init_user_ns, realpath->dentry, fa);
+}
+
 int ovl_fileattr_set(struct user_namespace *mnt_userns,
 		     struct dentry *dentry, struct fileattr *fa)
 {
 	struct inode *inode = d_inode(dentry);
-	struct dentry *upperdentry;
+	struct path upperpath;
 	const struct cred *old_cred;
 	int err;
 
@@ -541,12 +550,10 @@ int ovl_fileattr_set(struct user_namespace *mnt_userns,
 
 	err = ovl_copy_up(dentry);
 	if (!err) {
-		upperdentry = ovl_dentry_upper(dentry);
+		ovl_path_real(dentry, &upperpath);
 
 		old_cred = ovl_override_creds(inode->i_sb);
-		err = ovl_security_fileattr(dentry, fa, true);
-		if (!err)
-			err = vfs_fileattr_set(&init_user_ns, upperdentry, fa);
+		err = ovl_real_fileattr_set(&upperpath, fa);
 		revert_creds(old_cred);
 		ovl_copyflags(ovl_inode_real(inode), inode);
 	}
@@ -555,17 +562,28 @@ out:
 	return err;
 }
 
+int ovl_real_fileattr_get(struct path *realpath, struct fileattr *fa)
+{
+	int err;
+
+	err = ovl_security_fileattr(realpath, fa, false);
+	if (err)
+		return err;
+
+	return vfs_fileattr_get(realpath->dentry, fa);
+}
+
 int ovl_fileattr_get(struct dentry *dentry, struct fileattr *fa)
 {
 	struct inode *inode = d_inode(dentry);
-	struct dentry *realdentry = ovl_dentry_real(dentry);
+	struct path realpath;
 	const struct cred *old_cred;
 	int err;
 
+	ovl_path_real(dentry, &realpath);
+
 	old_cred = ovl_override_creds(inode->i_sb);
-	err = ovl_security_fileattr(dentry, fa, false);
-	if (!err)
-		err = vfs_fileattr_get(realdentry, fa);
+	err = ovl_real_fileattr_get(&realpath, fa);
 	revert_creds(old_cred);
 
 	return err;