fs: add FS_XFLAG_VERITY for fs-verity files

fs-verity introduced inode flag for inodes with enabled fs-verity on
them. This patch adds FS_XFLAG_VERITY file attribute which can be
retrieved with FS_IOC_FSGETXATTR ioctl() and file_getattr() syscall.

This flag is read-only and can not be set with corresponding set ioctl()
and file_setattr(). The FS_IOC_SETFLAGS requires file to be opened for
writing which is not allowed for verity files. The FS_IOC_FSSETXATTR and
file_setattr() clears this flag from the user input.

As this is now common flag for both flag interfaces (flags/xflags) add
it to overlapping flags list to exclude it from overwrite.

Signed-off-by: Andrey Albershteyn <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Reviewed-by: Darrick J. Wong <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>

Documentation/filesystems/fsverity.rst

···
 FS_IOC_GETFLAGS and FS_IOC_MEASURE_VERITY because it doesn't require
 opening the file, and opening verity files can be expensive.
 
+FS_IOC_FSGETXATTR
+-----------------
+
+Since Linux v7.0, the FS_IOC_FSGETXATTR ioctl sets FS_XFLAG_VERITY (0x00020000)
+in the returned flags when the file has verity enabled. Note that this attribute
+cannot be set with FS_IOC_FSSETXATTR as enabling verity requires input
+parameters. See FS_IOC_ENABLE_VERITY.
+
+file_getattr
+------------
+
+Since Linux v7.0, the file_getattr() syscall sets FS_XFLAG_VERITY (0x00020000)
+in the returned flags when the file has verity enabled. Note that this attribute
+cannot be set with file_setattr() as enabling verity requires input parameters.
+See FS_IOC_ENABLE_VERITY.
+
 .. _accessing_verity_files:
 
 Accessing verity files

fs/file_attr.c

···
 		fa->flags |= FS_DAX_FL;
 	if (fa->fsx_xflags & FS_XFLAG_PROJINHERIT)
 		fa->flags |= FS_PROJINHERIT_FL;
+	if (fa->fsx_xflags & FS_XFLAG_VERITY)
+		fa->flags |= FS_VERITY_FL;
 }
 EXPORT_SYMBOL(fileattr_fill_xflags);
 
···
 		fa->fsx_xflags |= FS_XFLAG_DAX;
 	if (fa->flags & FS_PROJINHERIT_FL)
 		fa->fsx_xflags |= FS_XFLAG_PROJINHERIT;
+	if (fa->flags & FS_VERITY_FL)
+		fa->fsx_xflags |= FS_XFLAG_VERITY;
 }
 EXPORT_SYMBOL(fileattr_fill_flags);
 

include/linux/fileattr.h

···
 #define FS_COMMON_FL \
 	(FS_SYNC_FL | FS_IMMUTABLE_FL | FS_APPEND_FL | \
 	 FS_NODUMP_FL |	FS_NOATIME_FL | FS_DAX_FL | \
-	 FS_PROJINHERIT_FL)
+	 FS_PROJINHERIT_FL | FS_VERITY_FL)
 
 #define FS_XFLAG_COMMON \
 	(FS_XFLAG_SYNC | FS_XFLAG_IMMUTABLE | FS_XFLAG_APPEND | \
 	 FS_XFLAG_NODUMP | FS_XFLAG_NOATIME | FS_XFLAG_DAX | \
-	 FS_XFLAG_PROJINHERIT)
+	 FS_XFLAG_PROJINHERIT | FS_XFLAG_VERITY)
 
 /* Read-only inode flags */
 #define FS_XFLAG_RDONLY_MASK \
-	(FS_XFLAG_PREALLOC | FS_XFLAG_HASATTR)
+	(FS_XFLAG_PREALLOC | FS_XFLAG_HASATTR | FS_XFLAG_VERITY)
 
 /* Flags to indicate valid value of fsx_ fields */
 #define FS_XFLAG_VALUES_MASK \

include/uapi/linux/fs.h

···
 #define FS_XFLAG_FILESTREAM	0x00004000	/* use filestream allocator */
 #define FS_XFLAG_DAX		0x00008000	/* use DAX for IO */
 #define FS_XFLAG_COWEXTSIZE	0x00010000	/* CoW extent size allocator hint */
+#define FS_XFLAG_VERITY		0x00020000	/* fs-verity enabled */
 #define FS_XFLAG_HASATTR	0x80000000	/* no DIFLAG for this	*/
 
 /* the read-only stuff doesn't really belong here, but any other place is