Implement File Attribute Support

We add support for lsattr and chattr to resolve a regression caused
by 88c283952f0bfeab54612f9ce666601d83c4244f that broke Python's
xattr.list(). That changet broke Gentoo Portage's FEATURES=xattr,
which depended on Python's xattr.list().

Only attributes common to both Solaris and Linux are supported. These
are 'a', 'd' and 'i' in Linux's lsattr and chattr commands. File
attributes exclusive to Solaris are present in the ZFS code, but cannot
be accessed or modified through this method.  That was the case prior to
this patch. The resolution of issue zfsonlinux/zfs#229 should implement
some method to permit access and modification of Solaris-specific
attributes.

References:
  https://bugs.gentoo.org/show_bug.cgi?id=483516

Original-patch-by: Brian Behlendorf <[email protected]>
Signed-off-by: Richard Yao <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #1691

1 files changed, 94 insertions, 3 deletions

diff --git a/module/zfs/zpl_file.c b/module/zfs/zpl_file.c
index 3737bb519..2a7bcb9b0 100644
--- a/module/zfs/zpl_file.c
+++ b/module/zfs/zpl_file.c
@@ -520,13 +520,104 @@ zpl_fallocate(struct file *filp, int mode, loff_t offset, loff_t len)
 }
 #endif /* HAVE_FILE_FALLOCATE */
 
+/*
+ * Map zfs file z_pflags (xvattr_t) to linux file attributes. Only file
+ * attributes common to both Linux and Solaris are mapped.
+ */
+static int
+zpl_ioctl_getflags(struct file *filp, void __user *arg)
+{
+	struct inode *ip = filp->f_dentry->d_inode;
+	unsigned int ioctl_flags = 0;
+	uint64_t zfs_flags = ITOZ(ip)->z_pflags;
+	int error;
+
+	if (zfs_flags & ZFS_IMMUTABLE)
+		ioctl_flags |= FS_IMMUTABLE_FL;
+
+	if (zfs_flags & ZFS_APPENDONLY)
+		ioctl_flags |= FS_APPEND_FL;
+
+	if (zfs_flags & ZFS_NODUMP)
+		ioctl_flags |= FS_NODUMP_FL;
+
+	ioctl_flags &= FS_FL_USER_VISIBLE;
+
+	error = copy_to_user(arg, &ioctl_flags, sizeof (ioctl_flags));
+
+	return (error);
+}
+
+/*
+ * fchange() is a helper macro to detect if we have been asked to change a
+ * flag. This is ugly, but the requirement that we do this is a consequence of
+ * how the Linux file attribute interface was designed. Another consequence is
+ * that concurrent modification of files suffers from a TOCTOU race. Neither
+ * are things we can fix without modifying the kernel-userland interface, which
+ * is outside of our jurisdiction.
+ */
+
+#define	fchange(f0, f1, b0, b1) ((((f0) & (b0)) == (b0)) != \
+	(((b1) & (f1)) == (f1)))
+
+static int
+zpl_ioctl_setflags(struct file *filp, void __user *arg)
+{
+	struct inode	*ip = filp->f_dentry->d_inode;
+	uint64_t	zfs_flags = ITOZ(ip)->z_pflags;
+	unsigned int	ioctl_flags;
+	cred_t		*cr = CRED();
+	xvattr_t	xva;
+	xoptattr_t	*xoap;
+	int		error;
+
+	if (copy_from_user(&ioctl_flags, arg, sizeof (ioctl_flags)))
+		return (-EFAULT);
+
+	if ((ioctl_flags & ~(FS_IMMUTABLE_FL | FS_APPEND_FL | FS_NODUMP_FL)))
+		return (-EOPNOTSUPP);
+
+	if ((ioctl_flags & ~(FS_FL_USER_MODIFIABLE)))
+		return (-EACCES);
+
+	if ((fchange(ioctl_flags, zfs_flags, FS_IMMUTABLE_FL, ZFS_IMMUTABLE) ||
+	    fchange(ioctl_flags, zfs_flags, FS_APPEND_FL, ZFS_APPENDONLY)) &&
+	    !capable(CAP_LINUX_IMMUTABLE))
+		return (-EACCES);
+
+	if (!zpl_inode_owner_or_capable(ip))
+		return (-EACCES);
+
+	xva_init(&xva);
+	xoap = xva_getxoptattr(&xva);
+
+	XVA_SET_REQ(&xva, XAT_IMMUTABLE);
+	if (ioctl_flags & FS_IMMUTABLE_FL)
+		xoap->xoa_immutable = B_TRUE;
+
+	XVA_SET_REQ(&xva, XAT_APPENDONLY);
+	if (ioctl_flags & FS_APPEND_FL)
+		xoap->xoa_appendonly = B_TRUE;
+
+	XVA_SET_REQ(&xva, XAT_NODUMP);
+	if (ioctl_flags & FS_NODUMP_FL)
+		xoap->xoa_nodump = B_TRUE;
+
+	crhold(cr);
+	error = -zfs_setattr(ip, (vattr_t *)&xva, 0, cr);
+	crfree(cr);
+
+	return (error);
+}
+
 static long
 zpl_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	switch (cmd) {
-	case ZFS_IOC_GETFLAGS:
-	case ZFS_IOC_SETFLAGS:
-		return (-EOPNOTSUPP);
+	case FS_IOC_GETFLAGS:
+		return (zpl_ioctl_getflags(filp, (void *)arg));
+	case FS_IOC_SETFLAGS:
+		return (zpl_ioctl_setflags(filp, (void *)arg));
 	default:
 		return (-ENOTTY);
 	}