xfs: add parent pointer validator functions

The attr name of a parent pointer is a string, and the attr value of a
parent pointer is (more or less) a file handle.  So we need to modify
attr_namecheck to verify the parent pointer name, and add a
xfs_parent_valuecheck function to sanitize the handle.  At the same
time, we need to validate attr values during log recovery if the xattr
is really a parent pointer.
Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
[djwong: move functions to xfs_parent.c, adjust for new disk format]
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/Makefile

@@ -42,6 +42,7 @@ xfs-y				+= $(addprefix libxfs/, \
 				   xfs_inode_buf.o \
 				   xfs_log_rlimit.o \
 				   xfs_ag_resv.o \
+				   xfs_parent.o \
 				   xfs_rmap.o \
 				   xfs_rmap_btree.o \
 				   xfs_refcount.o \

fs/xfs/libxfs/xfs_attr.c

@@ -26,6 +26,7 @@
 #include "xfs_trace.h"
 #include "xfs_attr_item.h"
 #include "xfs_xattr.h"
+#include "xfs_parent.h"
 
 struct kmem_cache		*xfs_attr_intent_cache;
 
@@ -1568,6 +1569,10 @@ xfs_attr_namecheck(
 	if (length >= MAXNAMELEN)
 		return false;
 
+	/* Parent pointers have their own validation. */
+	if (attr_flags & XFS_ATTR_PARENT)
+		return xfs_parent_namecheck(attr_flags, name, length);
+
 	/* There shouldn't be any nulls here */
 	return !memchr(name, 0, length);
 }

fs/xfs/libxfs/xfs_parent.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2022-2024 Oracle.
+ * All rights reserved.
+ */
+#include "xfs.h"
+#include "xfs_fs.h"
+#include "xfs_format.h"
+#include "xfs_da_format.h"
+#include "xfs_log_format.h"
+#include "xfs_shared.h"
+#include "xfs_trans_resv.h"
+#include "xfs_mount.h"
+#include "xfs_bmap_btree.h"
+#include "xfs_inode.h"
+#include "xfs_error.h"
+#include "xfs_trace.h"
+#include "xfs_trans.h"
+#include "xfs_da_btree.h"
+#include "xfs_attr.h"
+#include "xfs_dir2.h"
+#include "xfs_dir2_priv.h"
+#include "xfs_attr_sf.h"
+#include "xfs_bmap.h"
+#include "xfs_defer.h"
+#include "xfs_log.h"
+#include "xfs_xattr.h"
+#include "xfs_parent.h"
+#include "xfs_trans_space.h"
+
+/*
+ * Parent pointer attribute handling.
+ *
+ * Because the attribute name is a filename component, it will never be longer
+ * than 255 bytes and must not contain nulls or slashes.  These are roughly the
+ * same constraints that apply to attribute names.
+ *
+ * The attribute value must always be a struct xfs_parent_rec.  This means the
+ * attribute will never be in remote format because 12 bytes is nowhere near
+ * xfs_attr_leaf_entsize_local_max() (~75% of block size).
+ *
+ * Creating a new parent attribute will always create a new attribute - there
+ * should never, ever be an existing attribute in the tree for a new inode.
+ * ENOSPC behavior is problematic - creating the inode without the parent
+ * pointer is effectively a corruption, so we allow parent attribute creation
+ * to dip into the reserve block pool to avoid unexpected ENOSPC errors from
+ * occurring.
+ */
+
+/* Return true if parent pointer attr name is valid. */
+bool
+xfs_parent_namecheck(
+	unsigned int			attr_flags,
+	const void			*name,
+	size_t				length)
+{
+	/*
+	 * Parent pointers always use logged operations, so there should never
+	 * be incomplete xattrs.
+	 */
+	if (attr_flags & XFS_ATTR_INCOMPLETE)
+		return false;
+
+	return xfs_dir2_namecheck(name, length);
+}
+
+/* Return true if parent pointer attr value is valid. */
+bool
+xfs_parent_valuecheck(
+	struct xfs_mount		*mp,
+	const void			*value,
+	size_t				valuelen)
+{
+	const struct xfs_parent_rec	*rec = value;
+
+	if (!xfs_has_parent(mp))
+		return false;
+
+	/* The xattr value must be a parent record. */
+	if (valuelen != sizeof(struct xfs_parent_rec))
+		return false;
+
+	/* The parent record must be local. */
+	if (value == NULL)
+		return false;
+
+	/* The parent inumber must be valid. */
+	if (!xfs_verify_dir_ino(mp, be64_to_cpu(rec->p_ino)))
+		return false;
+
+	return true;
+}

fs/xfs/libxfs/xfs_parent.h

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2022-2024 Oracle.
+ * All Rights Reserved.
+ */
+#ifndef	__XFS_PARENT_H__
+#define	__XFS_PARENT_H__
+
+/* Metadata validators */
+bool xfs_parent_namecheck(unsigned int attr_flags, const void *name,
+		size_t length);
+bool xfs_parent_valuecheck(struct xfs_mount *mp, const void *value,
+		size_t valuelen);
+
+#endif /* __XFS_PARENT_H__ */

fs/xfs/xfs_attr_item.c

@@ -27,6 +27,7 @@
 #include "xfs_error.h"
 #include "xfs_log_priv.h"
 #include "xfs_log_recover.h"
+#include "xfs_parent.h"
 
 struct kmem_cache		*xfs_attri_cache;
 struct kmem_cache		*xfs_attrd_cache;
@@ -973,6 +974,15 @@ xfs_attri_validate_value_iovec(
 		return NULL;
 	}
 
+	if ((attri_formatp->alfi_attr_filter & XFS_ATTR_PARENT) &&
+	    !xfs_parent_valuecheck(mp, iovec->i_addr, value_len)) {
+		XFS_CORRUPTION_ERROR(__func__, XFS_ERRLEVEL_LOW, mp,
+				attri_formatp, sizeof(*attri_formatp));
+		XFS_CORRUPTION_ERROR(__func__, XFS_ERRLEVEL_LOW, mp,
+				iovec->i_addr, iovec->i_len);
+		return NULL;
+	}
+
 	return iovec->i_addr;
 }