xfs: clear kernel only flags in XFS_IOC_ATTRMULTI_BY_HANDLE

Don't allow passing arbitrary flags as they change behavior including
memory allocation that the call stack is not prepared for.

Fixes: ddbca70c ("xfs: allocate xattr buffer on demand")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/libxfs/xfs_attr.h

@@ -26,7 +26,7 @@ struct xfs_attr_list_context;
  *========================================================================*/
 
 
-#define ATTR_DONTFOLLOW	0x0001	/* -- unused, from IRIX -- */
+#define ATTR_DONTFOLLOW	0x0001	/* -- ignored, from IRIX -- */
 #define ATTR_ROOT	0x0002	/* use attrs in root (trusted) namespace */
 #define ATTR_TRUST	0x0004	/* -- unused, from IRIX -- */
 #define ATTR_SECURE	0x0008	/* use attrs in security namespace */
@@ -37,7 +37,10 @@ struct xfs_attr_list_context;
 #define ATTR_KERNOVAL	0x2000	/* [kernel] get attr size only, not value */
 
 #define ATTR_INCOMPLETE	0x4000	/* [kernel] return INCOMPLETE attr keys */
-#define ATTR_ALLOC	0x8000	/* allocate xattr buffer on demand */
+#define ATTR_ALLOC	0x8000	/* [kernel] allocate xattr buffer on demand */
+
+#define ATTR_KERNEL_FLAGS \
+	(ATTR_KERNOTIME | ATTR_KERNOVAL | ATTR_INCOMPLETE | ATTR_ALLOC)
 
 #define XFS_ATTR_FLAGS \
 	{ ATTR_DONTFOLLOW, 	"DONTFOLLOW" }, \

fs/xfs/xfs_ioctl.c

@@ -462,6 +462,8 @@ xfs_attrmulti_by_handle(
 
 	error = 0;
 	for (i = 0; i < am_hreq.opcount; i++) {
+		ops[i].am_flags &= ~ATTR_KERNEL_FLAGS;
+
 		ops[i].am_error = strncpy_from_user((char *)attr_name,
 				ops[i].am_attrname, MAXNAMELEN);
 		if (ops[i].am_error == 0 || ops[i].am_error == MAXNAMELEN)

fs/xfs/xfs_ioctl32.c

@@ -450,6 +450,8 @@ xfs_compat_attrmulti_by_handle(
 
 	error = 0;
 	for (i = 0; i < am_hreq.opcount; i++) {
+		ops[i].am_flags &= ~ATTR_KERNEL_FLAGS;
+
 		ops[i].am_error = strncpy_from_user((char *)attr_name,
 				compat_ptr(ops[i].am_attrname),
 				MAXNAMELEN);