Blame SOURCES/0004-Use-rpmkeys-alone-to-verify-signature.patch

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From 9798e9ee85f1ba39c816fa08fd3d6168cc8b29e8 Mon Sep 17 00:00:00 2001
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From: Demi Marie Obenour <demi@invisiblethingslab.com>
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Date: Fri, 9 Apr 2021 13:03:03 -0400
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Subject: [PATCH] Use rpmkeys alone to verify signature
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This avoids having to actually parse the package to check its signature,
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which reduces attack surface.  If the output of rpmkeys cannot be
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parsed, we assume the package is corrupt (the most likely cause).
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---
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 dnf/rpm/miscutils.py | 126 ++++++++++++++++++++++---------------------
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 1 file changed, 66 insertions(+), 60 deletions(-)
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diff --git a/dnf/rpm/miscutils.py b/dnf/rpm/miscutils.py
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index 5f2621c2..9d5b2860 100644
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--- a/dnf/rpm/miscutils.py
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+++ b/dnf/rpm/miscutils.py
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@@ -13,47 +13,84 @@
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 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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 # Copyright 2003 Duke University
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-from __future__ import print_function, absolute_import
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-from __future__ import unicode_literals
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+from __future__ import print_function, absolute_import, unicode_literals
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-import rpm
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 import os
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 import subprocess
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 import logging
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-
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-from dnf.i18n import ucd
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-from dnf.i18n import _
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 from shutil import which
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+from dnf.i18n import _
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-logger = logging.getLogger('dnf')
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+_logger = logging.getLogger('dnf')
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+_rpmkeys_binary = None
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+def _find_rpmkeys_binary():
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+    global _rpmkeys_binary
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+    if _rpmkeys_binary is None:
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+        _rpmkeys_binary = which("rpmkeys")
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+        _logger.debug(_('Using rpmkeys executable at %s to verify signatures'),
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+                      _rpmkeys_binary)
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+    return _rpmkeys_binary
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-def _verifyPkgUsingRpmkeys(package, installroot, fdno):
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-    os.lseek(fdno, 0, os.SEEK_SET)
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-    rpmkeys_binary = '/usr/bin/rpmkeys'
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-    if not os.path.isfile(rpmkeys_binary):
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-        rpmkeys_binary = which("rpmkeys")
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-        logger.info(_('Using rpmkeys executable from {path} to verify signature for package: {package}.').format(
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-            path=rpmkeys_binary, package=package))
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+def _process_rpm_output(data):
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+    # No signatures or digests = corrupt package.
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+    # There is at least one line for -: and another (empty) entry after the
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+    # last newline.
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+    if len(data) < 3 or data[0] != b'-:' or data[-1]:
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+        return 2
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+    seen_sig, missing_key, not_trusted, not_signed = False, False, False, False
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+    for i in data[1:-1]:
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+        if b': BAD' in i:
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+            return 2
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+        elif i.endswith(b': NOKEY'):
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+            missing_key = True
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+        elif i.endswith(b': NOTTRUSTED'):
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+            not_trusted = True
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+        elif i.endswith(b': NOTFOUND'):
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+            not_signed = True
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+        elif not i.endswith(b': OK'):
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+            return 2
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+    if not_trusted:
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+        return 3
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+    elif missing_key:
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+        return 1
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+    elif not_signed:
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+        return 4
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+    # we still check return code, so this is safe
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+    return 0
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-    if not os.path.isfile(rpmkeys_binary):
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-        logger.critical(_('Cannot find rpmkeys executable to verify signatures.'))
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-        return 0
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+def _verifyPackageUsingRpmkeys(package, installroot):
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+    rpmkeys_binary = _find_rpmkeys_binary()
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+    if rpmkeys_binary is None or not os.path.isfile(rpmkeys_binary):
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+        _logger.critical(_('Cannot find rpmkeys executable to verify signatures.'))
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+        return 2
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-    args = ('rpmkeys', '--checksig', '--root', installroot, '--define', '_pkgverify_level all', '-')
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+    # "--define=_pkgverify_level all" enforces signature checking;
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+    # "--define=_pkgverify_flags 0x0" ensures that all signatures and digests
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+    # are checked.
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+    args = ('rpmkeys', '--checksig', '--root', installroot, '--verbose',
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+            '--define=_pkgverify_level all', '--define=_pkgverify_flags 0x0',
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+            '-')
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     with subprocess.Popen(
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             args=args,
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             executable=rpmkeys_binary,
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             env={'LC_ALL': 'C'},
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-            stdin=fdno,
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             stdout=subprocess.PIPE,
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-            cwd='/') as p:
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-        data, err = p.communicate()
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-    if p.returncode != 0 or data != b'-: digests signatures OK\n':
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-        return 0
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-    else:
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-        return 1
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+            cwd='/',
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+            stdin=package) as p:
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+        data = p.communicate()[0]
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+    returncode = p.returncode
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+    if type(returncode) is not int:
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+        raise AssertionError('Popen set return code to non-int')
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+    # rpmkeys can return something other than 0 or 1 in the case of a
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+    # fatal error (OOM, abort() called, SIGSEGV, etc)
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+    if returncode >= 2 or returncode < 0:
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+        return 2
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+    ret = _process_rpm_output(data.split(b'\n'))
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+    if ret:
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+        return ret
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+    return 2 if returncode else 0
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 def checkSig(ts, package):
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     """Takes a transaction set and a package, check it's sigs,
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@@ -63,40 +100,9 @@ def checkSig(ts, package):
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     return 3 if the key is not trusted
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     return 4 if the pkg is not gpg or pgp signed"""
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-    value = 4
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-    currentflags = ts.setVSFlags(0)
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-    fdno = os.open(package, os.O_RDONLY)
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+    fdno = os.open(package, os.O_RDONLY|os.O_NOCTTY|os.O_CLOEXEC)
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     try:
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-        hdr = ts.hdrFromFdno(fdno)
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-    except rpm.error as e:
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-        if str(e) == "public key not available":
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-            value = 1
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-        elif str(e) == "public key not trusted":
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-            value = 3
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-        elif str(e) == "error reading package header":
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-            value = 2
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-        else:
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-            raise ValueError('Unexpected error value %r from ts.hdrFromFdno when checking signature.' % str(e))
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-    else:
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-        # checks signature from an hdr
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-        string = '%|DSAHEADER?{%{DSAHEADER:pgpsig}}:{%|RSAHEADER?{%{RSAHEADER:pgpsig}}:' \
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-                 '{%|SIGGPG?{%{SIGGPG:pgpsig}}:{%|SIGPGP?{%{SIGPGP:pgpsig}}:{(none)}|}|}|}|'
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-        try:
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-            siginfo = hdr.sprintf(string)
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-            siginfo = ucd(siginfo)
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-
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-            if siginfo == '(none)':
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-                value = 4
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-            elif "Key ID" in siginfo and _verifyPkgUsingRpmkeys(package, ts.ts.rootDir, fdno):
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-                value = 0
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-            else:
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-                raise ValueError('Unexpected return value %r from hdr.sprintf when checking signature.' % siginfo)
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-        except UnicodeDecodeError:
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-            pass
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-
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-        del hdr
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-
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-    os.close(fdno)
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-
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-    ts.setVSFlags(currentflags)  # put things back like they were before
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+        value = _verifyPackageUsingRpmkeys(fdno, ts.ts.rootDir)
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+    finally:
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+        os.close(fdno)
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     return value
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-- 
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2.35.1
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