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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH 6/6] tools/pygrub: Hook libfsimage's fdopen() to pygrub
This patch increases the security posture by removing the need to grant
filesystem access to the depriv pygrub. Using libfsimage's fdopen(), the
parent thread in the depriv procedure can simply ensure all the appropriate
file descriptors are present before revoking permissions to the filesystem.
A convenient usability side-effect is that it's no longer required for the
restricted user to have access to the disk, because the depriv thread
already has the file descriptor open by its parent.
Signed-off-by: Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>
---
docs/man/xl.cfg.5.pod.in | 6 +-
tools/pygrub/src/ExtLinuxConf.py | 20 ++++---
tools/pygrub/src/GrubConf.py | 29 ++++++----
tools/pygrub/src/LiloConf.py | 20 ++++---
tools/pygrub/src/pygrub | 95 ++++++++------------------------
5 files changed, 68 insertions(+), 102 deletions(-)
diff --git a/docs/man/xl.cfg.5.pod.in b/docs/man/xl.cfg.5.pod.in
index 2e234b450e..e3fd2e37eb 100644
--- a/docs/man/xl.cfg.5.pod.in
+++ b/docs/man/xl.cfg.5.pod.in
@@ -1704,8 +1704,7 @@ See docs/features/qemu-deprivilege.pandoc for more
information
on how to setup the unprivileged users.
Note that running the bootloader in restricted mode also implies using
-non-interactive mode, and the disk image must be readable by the
-restricted user.
+non-interactive mode.
=item B<bootloader_user=USERNAME>
@@ -2768,8 +2767,7 @@ See docs/features/qemu-deprivilege.pandoc for more
information
on how to setup the unprivileged users.
Note that running the bootloader in restricted mode also implies using
-non-interactive mode, and the disk image must be readable by the
-restricted user.
+non-interactive mode.
=item B<bootloader_user=USERNAME>
diff --git a/tools/pygrub/src/ExtLinuxConf.py b/tools/pygrub/src/ExtLinuxConf.py
index 4e990a9304..f2e9a81013 100644
--- a/tools/pygrub/src/ExtLinuxConf.py
+++ b/tools/pygrub/src/ExtLinuxConf.py
@@ -123,6 +123,7 @@ class ExtLinuxImage(object):
class ExtLinuxConfigFile(object):
def __init__(self, fn = None):
self.filename = fn
+ self.file = None
self.images = []
self.timeout = -1
self._default = 0
@@ -138,16 +139,21 @@ class ExtLinuxConfigFile(object):
def parse(self, buf = None):
if buf is None:
- if self.filename is None:
+ if not self.filename and not self.file:
raise ValueError("No config file defined to parse!")
- f = open(self.filename, 'r')
- lines = f.readlines()
- f.close()
- else:
- lines = buf.split("\n")
+ if self.file:
+ buf = file.read()
+ path = self.file.name
+ else:
+ f = open(self.filename, 'r')
+ buf = f.read()
+ f.close()
+ lines = buf.split("\n")
+
+ if not path:
+ path = os.path.dirname(self.filename)
- path = os.path.dirname(self.filename)
img = []
for l in lines:
l = l.strip()
diff --git a/tools/pygrub/src/GrubConf.py b/tools/pygrub/src/GrubConf.py
index 580c9628ca..96b79b89a7 100644
--- a/tools/pygrub/src/GrubConf.py
+++ b/tools/pygrub/src/GrubConf.py
@@ -170,6 +170,7 @@ class GrubImage(_GrubImage):
class _GrubConfigFile(object):
def __init__(self, fn = None):
self.filename = fn
+ self.file = None
self.images = []
self.timeout = -1
self._default = 0
@@ -271,14 +272,16 @@ class GrubConfigFile(_GrubConfigFile):
def parse(self, buf = None):
if buf is None:
- if self.filename is None:
+ if not self.filename and not self.file:
raise ValueError("No config file defined to parse!")
- f = open(self.filename, 'r')
- lines = f.readlines()
- f.close()
- else:
- lines = buf.split("\n")
+ if self.file:
+ buf = file.read()
+ else:
+ f = open(self.filename, 'r')
+ buf = f.read()
+ f.close()
+ lines = buf.split("\n")
img = None
title = ""
@@ -370,14 +373,16 @@ class Grub2ConfigFile(_GrubConfigFile):
def parse(self, buf = None):
if buf is None:
- if self.filename is None:
+ if not self.filename and not self.file:
raise ValueError("No config file defined to parse!")
- f = open(self.filename, 'r')
- lines = f.readlines()
- f.close()
- else:
- lines = buf.split("\n")
+ if self.file:
+ buf = file.read()
+ else:
+ f = open(self.filename, 'r')
+ buf = f.read()
+ f.close()
+ lines = buf.split("\n")
in_function = False
img = None
diff --git a/tools/pygrub/src/LiloConf.py b/tools/pygrub/src/LiloConf.py
index e3bfcb5244..73f8fcb214 100644
--- a/tools/pygrub/src/LiloConf.py
+++ b/tools/pygrub/src/LiloConf.py
@@ -90,6 +90,7 @@ class LiloImage(object):
class LiloConfigFile(object):
def __init__(self, fn = None):
self.filename = fn
+ self.file = None
self.images = []
self.timeout = -1
self._default = 0
@@ -99,16 +100,21 @@ class LiloConfigFile(object):
def parse(self, buf = None):
if buf is None:
- if self.filename is None:
+ if not self.filename and not self.file:
raise ValueError("No config file defined to parse!")
- f = open(self.filename, 'r')
- lines = f.readlines()
- f.close()
- else:
- lines = buf.split("\n")
+ if self.file:
+ buf = file.read()
+ path = self.file.name
+ else:
+ f = open(self.filename, 'r')
+ buf = f.read()
+ f.close()
+ lines = buf.split("\n")
+
+ if not path:
+ path = os.path.dirname(self.filename)
- path = os.path.dirname(self.filename)
img = []
for l in lines:
l = l.strip()
diff --git a/tools/pygrub/src/pygrub b/tools/pygrub/src/pygrub
index b96bdfd849..123e9c40ad 100755
--- a/tools/pygrub/src/pygrub
+++ b/tools/pygrub/src/pygrub
@@ -66,14 +66,6 @@ def unshare(flags):
# Undo it so that every mount done in the NS stay confined within it.
subprocess.check_output(["mount", "--make-rprivate", "/"])
-def bind_mount(src, dst, options):
- open(dst, "a").close() # touch
-
- rc = subprocess.call(["mount", "--bind", "-o", options, src, dst])
- if rc != 0:
- raise RuntimeError("bad_mount: src=%s dst=%s opts=%s" %
- (src, dst, options))
-
def downgrade_rlimits():
# Wipe the authority to use unrequired resources
resource.setrlimit(resource.RLIMIT_NPROC, (0, 0))
@@ -103,7 +95,7 @@ def downgrade_rlimits():
resource.setrlimit(resource.RLIMIT_FSIZE, (fsize, fsize))
-def depriv(output_directory, output, device, uid, path_kernel, path_ramdisk):
+def depriv(output_directory, uid, path_kernel, path_ramdisk):
# The only point of this call is to force the loading of libfsimage.
# That way, we don't need to bind-mount it into the chroot
rc = xenfsimage.init()
@@ -114,7 +106,7 @@ def depriv(output_directory, output, device, uid,
path_kernel, path_ramdisk):
# Create a temporary directory for the chroot
chroot = tempfile.mkdtemp(prefix=str(uid)+'-', dir=output_directory) + '/'
- device_path = '/device'
+ os.chmod(chroot, 0o700)
pid = os.fork()
if pid:
@@ -129,16 +121,7 @@ def depriv(output_directory, output, device, uid,
path_kernel, path_ramdisk):
if rc != 0 or os.path.getsize(path) == 0:
os.unlink(path)
- # Unshare(CLONE_NEWNS) ensures this is not required, but that's not
- # present on *BSD, so recursively unmount everything if needed.
- # Quietly.
- with open('/dev/null', 'w') as devnull:
- subprocess.call(["umount", "-f", chroot + device_path],
- stdout=devnull, stderr=devnull)
- subprocess.call(["umount", "-f", chroot],
- stdout=devnull, stderr=devnull)
os.rmdir(chroot)
-
sys.exit(rc)
# By unsharing the namespace we're making sure it's all bulk-released
@@ -150,20 +133,6 @@ def depriv(output_directory, output, device, uid,
path_kernel, path_ramdisk):
# Set sensible limits using the setrlimit interface
downgrade_rlimits()
- # We'll mount tmpfs on the chroot to ensure the deprivileged child
- # cannot affect the persistent state. It's RW now in order to
- # bind-mount the device, but note it's remounted RO after that.
- rc = subprocess.call(["mount", "-t", "tmpfs", "none", chroot])
- if rc != 0:
- raise RuntimeError("mount_tmpfs rc=%d dst=\"%s\"" % (rc, chroot))
-
- # Bind the untrusted device RO
- bind_mount(device, chroot + device_path, "ro,nosuid,noexec")
-
- rc = subprocess.call(["mount", "-t", "tmpfs", "-o",
"remount,ro,nosuid,noexec,nodev", "none", chroot])
- if rc != 0:
- raise RuntimeError("remount_tmpfs rc=%d dst=\"%s\"" % (rc, chroot))
-
# Drop superpowers!
os.chroot(chroot)
os.chdir('/')
@@ -171,15 +140,7 @@ def depriv(output_directory, output, device, uid,
path_kernel, path_ramdisk):
os.setgroups([uid])
os.setuid(uid)
- return device_path
-
-def read_size_roundup(fd, size):
- if platform.system() != 'FreeBSD':
- return size
- st = os.fstat(fd)
- if (not stat.S_ISCHR(st.st_mode)):
- return size
- # Round up to sector size if it's a raw character device
+def round_up_to_sectorsize(size):
return (((size)+((SECTOR_SIZE)-1))&(~((SECTOR_SIZE)-1)))
def enable_cursor(ison):
@@ -196,9 +157,8 @@ def enable_cursor(ison):
DISK_TYPE_RAW, DISK_TYPE_HYBRIDISO, DISK_TYPE_DOS = range(3)
def identify_disk_image(file):
"""Detect DOS partition table or HybridISO format."""
- fd = os.open(file, os.O_RDONLY)
- buf = os.read(fd, read_size_roundup(fd, 0x8006))
- os.close(fd)
+ file.seek(0, 0)
+ buf = file.read(0x8200)
if len(buf) >= 512 and \
struct.unpack("H", buf[0x1fe: 0x200]) == (0xaa55,):
@@ -215,10 +175,8 @@ V_ROOT=0x2
def get_solaris_slice(file, offset):
"""Find the root slice in a Solaris VTOC."""
- fd = os.open(file, os.O_RDONLY)
- os.lseek(fd, offset + (DK_LABEL_LOC * SECTOR_SIZE), 0)
- buf = os.read(fd, 512)
- os.close(fd)
+ file.seek(offset + (DK_LABEL_LOC * SECTOR_SIZE), 0)
+ buf = file.read(512)
if struct.unpack("<H", buf[508:510])[0] != DKL_MAGIC:
raise RuntimeError("Invalid disklabel magic")
@@ -234,9 +192,8 @@ def get_solaris_slice(file, offset):
raise RuntimeError("No root slice found")
def get_fs_offset_gpt(file):
- fd = os.open(file, os.O_RDONLY)
- os.lseek(fd, SECTOR_SIZE, 0)
- buf = os.read(fd, 512)
+ file.seek(512, 0)
+ buf = file.read(512)
partcount = struct.unpack("<L", buf[80:84])[0]
partsize = struct.unpack("<L", buf[84:88])[0]
i = partcount
@@ -267,9 +224,8 @@ def get_partition_offsets(file):
else:
raise ValueError('Unhandled image type returnd by
identify_disk_image(): %d' % (image_type,))
- fd = os.open(file, os.O_RDONLY)
- buf = os.read(fd, 512)
- os.close(fd)
+ file.seek(0, 0)
+ buf = file.read(512)
for poff in (446, 462, 478, 494): # partition offsets
# MBR contains a 16 byte descriptor per partition
@@ -565,9 +521,6 @@ class Grub:
"""Read the given file to parse the config. If fs = None, then
we're being given a raw config file rather than a disk image."""
- if not os.access(fn, os.R_OK):
- raise RuntimeError("Unable to access %s" %(fn,))
-
cfg_list = [(x,grub.GrubConf.Grub2ConfigFile) for x in
["/boot/grub/grub.cfg", "/grub/grub.cfg",
"/boot/grub2/grub.cfg", "/grub2/grub.cfg"]] + \
[(x,grub.ExtLinuxConf.ExtLinuxConfigFile) for x in
["/boot/isolinux/isolinux.cfg",
@@ -582,7 +535,8 @@ class Grub:
# set the config file and parse it
for f,parser in cfg_list:
self.cf = parser()
- self.cf.filename = fn
+ self.cf.filename = None
+ self.cf.fd = file
self.cf.parse()
return
@@ -591,6 +545,7 @@ class Grub:
print("Using %s to parse %s" % (parser,f), file=sys.stderr)
self.cf = parser()
self.cf.filename = f
+ self.cf.fd = None
break
if self.__dict__.get('cf', None) is None:
raise RuntimeError("couldn't find bootloader config file in the
image provided.")
@@ -880,7 +835,7 @@ if __name__ == "__main__":
def usage():
print("Usage: %s [-q|--quiet] [-i|--interactive] [-l|--list-entries]
[-n|--not-really] [--output=] [--kernel=] [--ramdisk=] [--args=] [--entry=]
[--output-directory=] [--output-format=sxp|simple|simple0] [--runas=]
[--offset=] <image>" %(sys.argv[0],), file=sys.stderr)
- def copy_from_image(fs, file_to_read, file_type, fd_dst, path_dst,
not_really):
+ def copy_from_image(fs, file_to_read, file_type, fd_dst, not_really):
if not_really:
if fs.file_exists(file_to_read):
return "<%s:%s>" % (file_type, file_to_read)
@@ -898,14 +853,7 @@ if __name__ == "__main__":
os.close(fd_dst)
del datafile
return
- try:
- os.write(fd_dst, data)
- except Exception as e:
- print(e, file=sys.stderr)
- if path_dst:
- os.unlink(path_dst)
- del datafile
- sys.exit("Error writing temporary copy of "+file_type)
+ os.write(fd_dst, data)
dataoff += len(data)
try:
@@ -1020,13 +968,15 @@ if __name__ == "__main__":
(fd_ramdisk, path_ramdisk) = tempfile.mkstemp(prefix="boot_ramdisk.",
dir=output_directory)
+ file = open(file, 'rb')
+
if output is None:
fd = sys.stdout.fileno()
else:
fd = os.open(output, os.O_WRONLY)
if uid:
- file = depriv(output_directory, output, file, uid, path_kernel,
path_ramdisk)
+ depriv(output_directory, uid, path_kernel, path_ramdisk)
# debug
if isconfig:
@@ -1049,9 +999,10 @@ if __name__ == "__main__":
if part_offs is None:
part_offs = get_partition_offsets(file)
+ file.seek(0, 0)
for offset in part_offs:
try:
- fs = xenfsimage.open(file, offset, bootfsoptions)
+ fs = xenfsimage.fdopen(os.dup(file.fileno()), offset,
bootfsoptions)
chosencfg = sniff_solaris(fs, incfg)
@@ -1083,13 +1034,13 @@ if __name__ == "__main__":
raise RuntimeError("Unable to find partition containing kernel")
copy_from_image(fs, chosencfg["kernel"], "kernel",
- fd_kernel, None if uid else path_kernel, not_really)
+ fd_kernel, not_really)
bootcfg["kernel"] = path_kernel
if chosencfg["ramdisk"]:
try:
copy_from_image(fs, chosencfg["ramdisk"], "ramdisk",
- fd_ramdisk, None if uid else path_ramdisk,
not_really)
+ fd_ramdisk, not_really)
except:
if not uid and not not_really:
os.unlink(path_kernel)
--
2.34.1
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