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backup: make hmac verification more defensive

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Check HMAC file size, read it as binary or with 'ascii' encoding only.
This commit is contained in:
Marek Marczykowski-Górecki 2017-02-25 02:28:54 +01:00
parent a6c7da6061
commit 751415434c
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GPG Key ID: 063938BA42CFA724
1 changed files with 11 additions and 3 deletions
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14
qubes/backup.py
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@ -61,6 +61,8 @@ CURRENT_BACKUP_FORMAT_VERSION = '4'
MAX_STDERR_BYTES = 1024 MAX_STDERR_BYTES = 1024
# header + qubes.xml max size # header + qubes.xml max size
HEADER_QUBES_XML_MAX_SIZE = 1024 * 1024 HEADER_QUBES_XML_MAX_SIZE = 1024 * 1024
# hmac file max size - regardless of backup format version!
HMAC_MAX_SIZE = 4096
BLKSIZE = 512 BLKSIZE = 512
@ -1597,6 +1599,11 @@ class BackupRestore(object):
passphrase = self.passphrase.encode('utf-8') passphrase = self.passphrase.encode('utf-8')
self.log.debug("Verifying file {}".format(filename)) self.log.debug("Verifying file {}".format(filename))
if os.stat(os.path.join(self.tmpdir, hmacfile)).st_size > \
HMAC_MAX_SIZE:
raise qubes.exc.QubesException('HMAC file {} too large'.format(
hmacfile))
if hmacfile != filename + ".hmac": if hmacfile != filename + ".hmac":
raise qubes.exc.QubesException( raise qubes.exc.QubesException(
"ERROR: expected hmac for {}, but got {}". "ERROR: expected hmac for {}, but got {}".
@ -1606,8 +1613,9 @@ class BackupRestore(object):
# in case of 'scrypt' _verify_hmac is only used for backup header # in case of 'scrypt' _verify_hmac is only used for backup header
assert filename == HEADER_FILENAME assert filename == HEADER_FILENAME
self._verify_and_decrypt(hmacfile, HEADER_FILENAME + '.dec') self._verify_and_decrypt(hmacfile, HEADER_FILENAME + '.dec')
if open(os.path.join(self.tmpdir, filename)).read() != \ if open(os.path.join(self.tmpdir, filename), 'rb').read() != \
open(os.path.join(self.tmpdir, filename + '.dec')).read(): open(os.path.join(self.tmpdir, filename + '.dec'),
'rb').read():
raise qubes.exc.QubesException( raise qubes.exc.QubesException(
'Invalid hmac on {}'.format(filename)) 'Invalid hmac on {}'.format(filename))
else: else:
@ -1625,7 +1633,7 @@ class BackupRestore(object):
else: else:
self.log.debug("Loading hmac for file {}".format(filename)) self.log.debug("Loading hmac for file {}".format(filename))
hmac = load_hmac(open(os.path.join(self.tmpdir, hmacfile), hmac = load_hmac(open(os.path.join(self.tmpdir, hmacfile),
'r').read()) 'r', encoding='ascii').read())
if len(hmac) > 0 and load_hmac(hmac_stdout.decode('ascii')) == hmac: if len(hmac) > 0 and load_hmac(hmac_stdout.decode('ascii')) == hmac:
os.unlink(os.path.join(self.tmpdir, hmacfile)) os.unlink(os.path.join(self.tmpdir, hmacfile))