diff options
Diffstat (limited to 'meta-security/classes/xattr-images.bbclass')
| -rw-r--r-- | meta-security/classes/xattr-images.bbclass | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/meta-security/classes/xattr-images.bbclass b/meta-security/classes/xattr-images.bbclass new file mode 100644 index 000000000..565a3fb6e --- /dev/null +++ b/meta-security/classes/xattr-images.bbclass @@ -0,0 +1,137 @@ +# Both Smack and IMA/EVM rely on xattrs. Inheriting this class ensures +# that these xattrs get preserved in tar and jffs2 images. +# +# It also fixes the rootfs so that the content of directories with +# SMACK::TRANSMUTE is correctly labelled. This is because pseudo does +# not know the special semantic of SMACK::TRANSMUTE and omits the +# updating of the Smack label when creating entries inside such a directory, +# for example /etc (see base-files_%.bbappend). Without the fixup, +# files already installed during the image creation would have different (and +# wrong) Smack labels. + +# xattr support is expected to be compiled into mtd-utils. We just need to +# use it. +EXTRA_IMAGECMD_jffs2_append = " --with-xattr" + +# By default, OE-core uses tar from the host, which may or may not have the +# --xattrs parameter which was introduced in 1.27. For image building we +# use a recent enough tar instead. +# +# The GNU documentation does not specify whether --xattrs-include is necessary. +# In practice, it turned out to be not needed when creating archives and +# required when extracting, but it seems prudent to use it in both cases. +IMAGE_DEPENDS_tar_append = " tar-replacement-native" +EXTRANATIVEPATH += "tar-native" +IMAGE_CMD_TAR = "tar --xattrs --xattrs-include=*" + +xattr_images_fix_transmute[dirs] = "${IMAGE_ROOTFS}" +python xattr_images_fix_transmute () { + # The recursive updating of the Smack label ensures that each entry + # has the label set for its parent directories if one of those was + # marked as transmuting. + # + # In addition, "_" is set explicitly on everything that would not + # have a label otherwise. This is a workaround for tools like swupd + # which transfers files from a rootfs onto a target device where Smack + # is active: on the target, each file gets assigned a label, typically + # the one from the process which creates it. swupd (or rather, the tools + # it is currently built on) knows how to set security.SMACK64="_" when + # it is set on the original files, but it does not know that it needs + # to remove that xattr when not set. + import os + import errno + + if getattr(os, 'getxattr', None): + # Python 3: os has xattr support. + def lgetxattr(f, attr): + try: + value = os.getxattr(f, attr, follow_symlinks=False) + return value.decode('utf8') + except OSError as ex: + if ex.errno == errno.ENODATA: + return None + + def lsetxattr(f, attr, value): + os.setxattr(f, attr.encode('utf8'), value.encode('utf8'), follow_symlinks=False) + else: + # Python 2: xattr support only in xattr module. + # + # Cannot use the 'xattr' module, it is not part of a standard Python + # installation. Instead re-implement using ctypes. Only has to be good + # enough for xattrs that are strings. Always operates on the symlinks themselves, + # not what they point to. + import ctypes + + # We cannot look up the xattr functions inside libc. That bypasses + # pseudo, which overrides these functions via LD_PRELOAD. Instead we have to + # find the function address and then create a ctypes function from it. + libdl = ctypes.CDLL("libdl.so.2") + _dlsym = libdl.dlsym + _dlsym.restype = ctypes.c_void_p + RTLD_DEFAULT = ctypes.c_void_p(0) + _lgetxattr = ctypes.CFUNCTYPE(ctypes.c_ssize_t, ctypes.c_char_p, ctypes.c_char_p, ctypes.c_void_p, ctypes.c_size_t, + use_errno=True)(_dlsym(RTLD_DEFAULT, 'lgetxattr')) + _lsetxattr = ctypes.CFUNCTYPE(ctypes.c_int, ctypes.c_char_p, ctypes.c_char_p, ctypes.c_void_p, ctypes.c_size_t, ctypes.c_int, + use_errno=True)(_dlsym(RTLD_DEFAULT, 'lsetxattr')) + + def lgetxattr(f, attr): + len = 32 + while True: + buffer = ctypes.create_string_buffer('\000' * len) + res = _lgetxattr(f, attr, buffer, ctypes.c_size_t(len)) + if res >= 0: + return buffer.value + else: + error = ctypes.get_errno() + if ctypes.get_errno() == errno.ERANGE: + len *= 2 + elif error == errno.ENODATA: + return None + else: + raise IOError(error, 'lgetxattr(%s, %s): %d = %s = %s' % + (f, attr, error, errno.errorcode[error], os.strerror(error))) + + def lsetxattr(f, attr, value): + res = _lsetxattr(f, attr, value, ctypes.c_size_t(len(value)), ctypes.c_int(0)) + if res != 0: + error = ctypes.get_errno() + raise IOError(error, 'lsetxattr(%s, %s, %s): %d = %s = %s' % + (f, attr, value, error, errno.errorcode[error], os.strerror(error))) + + def visit(path, deflabel, deftransmute): + isrealdir = os.path.isdir(path) and not os.path.islink(path) + curlabel = lgetxattr(path, 'security.SMACK64') + transmute = lgetxattr(path, 'security.SMACK64TRANSMUTE') == 'TRUE' + + if not curlabel: + # Since swupd doesn't remove the label from an updated file assigned by + # the target device's kernel upon unpacking the file from an update, + # we have to set the floor label explicitly even though it is the default label + # and thus adding it would create additional overhead. Otherwise this + # would result in hash mismatches reported by `swupd verify`. + lsetxattr(path, 'security.SMACK64', deflabel) + if not transmute and deftransmute and isrealdir: + lsetxattr(path, 'security.SMACK64TRANSMUTE', 'TRUE') + + # Identify transmuting directories and change the default Smack + # label inside them. In addition, directories themselves must become + # transmuting. + if isrealdir: + if transmute: + deflabel = lgetxattr(path, 'security.SMACK64') + deftransmute = True + if deflabel is None: + raise RuntimeError('%s: transmuting directory without Smack label' % path) + elif curlabel: + # Directory with explicit label set and not transmuting => do not + # change the content unless we run into another transmuting directory. + deflabel = '_' + deftransmute = False + + for entry in os.listdir(path): + visit(os.path.join(path, entry), deflabel, deftransmute) + + visit('.', '_', False) +} +# Same logic as in ima-evm-rootfs.bbclass: try to run as late as possible. +IMAGE_PREPROCESS_COMMAND_append_with-lsm-smack = " xattr_images_fix_transmute ; " |