Subject: [PATCH] gnu: dbus: Fix CVE-2019-12749.

From: Marius Bakke <[email-masked]>
Date: Sat, 15 Jun 2019 13:57:53 +0200

* gnu/packages/patches/dbus-CVE-2019-12749.patch: New file.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/glib.scm (dbus)[replacement]: New field.
(dbus/fixed): New variable.
---
 gnu/local.mk                                  |   1 +
 gnu/packages/glib.scm                         |   9 ++
 .../patches/dbus-CVE-2019-12749.patch         | 116 ++++++++++++++++++
 3 files changed, 126 insertions(+)
 create mode 100644 gnu/packages/patches/dbus-CVE-2019-12749.patch

diff --git a/gnu/local.mk b/gnu/local.mk
index 5b6dd31b11..f4331f8a95 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -740,6 +740,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/cursynth-wave-rand.patch			\
   %D%/packages/patches/cvs-2017-12836.patch			\
   %D%/packages/patches/dbus-helper-search-path.patch		\
+  %D%/packages/patches/dbus-CVE-2019-12749.patch		\
   %D%/packages/patches/dealii-mpi-deprecations.patch		\
   %D%/packages/patches/deja-dup-use-ref-keyword-for-iter.patch	\
   %D%/packages/patches/dfu-programmer-fix-libusb.patch		\
diff --git a/gnu/packages/glib.scm b/gnu/packages/glib.scm
index 7af7c86853..d75b963794 100644
--- a/gnu/packages/glib.scm
+++ b/gnu/packages/glib.scm
@@ -80,6 +80,7 @@
   (package
     (name "dbus")
     (version "1.12.12")
+    (replacement dbus/fixed)
     (source (origin
               (method url-fetch)
               (uri (string-append
@@ -146,6 +147,14 @@ or through unencrypted TCP/IP suitable for use behind a firewall with
 shared NFS home directories.")
     (license license:gpl2+)))                     ; or Academic Free License 2.1
 
+(define dbus/fixed
+  (package
+    (inherit dbus)
+    (source (origin
+              (inherit (package-source dbus))
+              (patches (append (search-patches "dbus-CVE-2019-12749.patch")
+                               (origin-patches (package-source dbus))))))))
+
 (define glib
   (package
    (name "glib")
diff --git a/gnu/packages/patches/dbus-CVE-2019-12749.patch b/gnu/packages/patches/dbus-CVE-2019-12749.patch
new file mode 100644
index 0000000000..12106f4589
--- /dev/null
+++ b/gnu/packages/patches/dbus-CVE-2019-12749.patch
@@ -0,0 +1,116 @@
+From 47b1a4c41004bf494b87370987b222c934b19016 Mon Sep 17 00:00:00 2001
+From: Simon McVittie <[email-masked]>
+Date: Thu, 30 May 2019 12:53:03 +0100
+Subject: [PATCH] auth: Reject DBUS_COOKIE_SHA1 for users other than the server
+ owner
+
+The DBUS_COOKIE_SHA1 authentication mechanism aims to prove ownership
+of a shared home directory by having the server write a secret "cookie"
+into a .dbus-keyrings subdirectory of the desired identity's home
+directory with 0700 permissions, and having the client prove that it can
+read the cookie. This never actually worked for non-malicious clients in
+the case where server uid != client uid (unless the server and client
+both have privileges, such as Linux CAP_DAC_OVERRIDE or traditional
+Unix uid 0) because an unprivileged server would fail to write out the
+cookie, and an unprivileged client would be unable to read the resulting
+file owned by the server.
+
+Additionally, since dbus 1.7.10 we have checked that ~/.dbus-keyrings
+is owned by the uid of the server (a side-effect of a check added to
+harden our use of XDG_RUNTIME_DIR), further ruling out successful use
+by a non-malicious client with a uid differing from the server's.
+
+Joe Vennix of Apple Information Security discovered that the
+implementation of DBUS_COOKIE_SHA1 was susceptible to a symbolic link
+attack: a malicious client with write access to its own home directory
+could manipulate a ~/.dbus-keyrings symlink to cause the DBusServer to
+read and write in unintended locations. In the worst case this could
+result in the DBusServer reusing a cookie that is known to the
+malicious client, and treating that cookie as evidence that a subsequent
+client connection came from an attacker-chosen uid, allowing
+authentication bypass.
+
+This is mitigated by the fact that by default, the well-known system
+dbus-daemon (since 2003) and the well-known session dbus-daemon (in
+stable releases since dbus 1.10.0 in 2015) only accept the EXTERNAL
+authentication mechanism, and as a result will reject DBUS_COOKIE_SHA1
+at an early stage, before manipulating cookies. As a result, this
+vulnerability only applies to:
+
+* system or session dbus-daemons with non-standard configuration
+* third-party dbus-daemon invocations such as at-spi2-core (although
+  in practice at-spi2-core also only accepts EXTERNAL by default)
+* third-party uses of DBusServer such as the one in Upstart
+
+Avoiding symlink attacks in a portable way is difficult, because APIs
+like openat() and Linux /proc/self/fd are not universally available.
+However, because DBUS_COOKIE_SHA1 already doesn't work in practice for
+a non-matching uid, we can solve this vulnerability in an easier way
+without regressions, by rejecting it early (before looking at
+~/.dbus-keyrings) whenever the requested identity doesn't match the
+identity of the process hosting the DBusServer.
+
+Signed-off-by: Simon McVittie <[email-masked]>
+Closes: https://gitlab.freedesktop.org/dbus/dbus/issues/269
+Closes: CVE-2019-12749
+---
+ dbus/dbus-auth.c | 32 ++++++++++++++++++++++++++++++++
+ 1 file changed, 32 insertions(+)
+
+diff --git a/dbus/dbus-auth.c b/dbus/dbus-auth.c
+index 37d8d4c9..7390a9d5 100644
+--- a/dbus/dbus-auth.c
++++ b/dbus/dbus-auth.c
+@@ -529,6 +529,7 @@ sha1_handle_first_client_response (DBusAuth         *auth,
+   DBusString tmp2;
+   dbus_bool_t retval = FALSE;
+   DBusError error = DBUS_ERROR_INIT;
++  DBusCredentials *myself = NULL;
+ 
+   _dbus_string_set_length (&auth->challenge, 0);
+   
+@@ -565,6 +566,34 @@ sha1_handle_first_client_response (DBusAuth         *auth,
+       return FALSE;
+     }
+ 
++  myself = _dbus_credentials_new_from_current_process ();
++
++  if (myself == NULL)
++    goto out;
++
++  if (!_dbus_credentials_same_user (myself, auth->desired_identity))
++    {
++      /*
++       * DBUS_COOKIE_SHA1 is not suitable for authenticating that the
++       * client is anyone other than the user owning the process
++       * containing the DBusServer: we probably aren't allowed to write
++       * to other users' home directories. Even if we can (for example
++       * uid 0 on traditional Unix or CAP_DAC_OVERRIDE on Linux), we
++       * must not, because the other user controls their home directory,
++       * and could carry out symlink attacks to make us read from or
++       * write to unintended locations. It's difficult to avoid symlink
++       * attacks in a portable way, so we just don't try. This isn't a
++       * regression, because DBUS_COOKIE_SHA1 never worked for other
++       * users anyway.
++       */
++      _dbus_verbose ("%s: client tried to authenticate as \"%s\", "
++                     "but that doesn't match this process",
++                     DBUS_AUTH_NAME (auth),
++                     _dbus_string_get_const_data (data));
++      retval = send_rejected (auth);
++      goto out;
++    }
++
+   /* we cache the keyring for speed, so here we drop it if it's the
+    * wrong one. FIXME caching the keyring here is useless since we use
+    * a different DBusAuth for every connection.
+@@ -679,6 +708,9 @@ sha1_handle_first_client_response (DBusAuth         *auth,
+   _dbus_string_zero (&tmp2);
+   _dbus_string_free (&tmp2);
+ 
++  if (myself != NULL)
++    _dbus_credentials_unref (myself);
++
+   return retval;
+ }
+ 
-- 
2.22.0