From 8105f53edfe4625f42477f2f7ca3339450227b8a Mon Sep 17 00:00:00 2001 From: "Darrick J. Wong" Date: Thu, 24 Aug 2023 17:00:55 -0700 Subject: [PATCH] xfsprogs: don't allow udisks to automount XFS filesystems with no prompt The unending stream of syzbot bug reports and overwrought filing of CVEs for corner case handling (i.e. things that distract from actual user complaints) in XFS has generated all sorts of of overheated rhetoric about how every bug is a Serious Security Issue(tm) because anyone can craft a malicious filesystem on a USB stick, insert the stick into a victim machine, and mount will trigger a bug in the kernel driver that leads to some compromise or DoS or something. I thought that nobody would be foolish enough to automount an XFS filesystem. What a fool I was! It turns out that udisks can be told that it's okay to automount things, and then GNOME will do exactly that. Including mounting mangled XFS filesystems! Turn off /this/ idiocy by adding a udev rule to tell udisks not to automount XFS filesystems. This will not stop a logged in user from unwittingly inserting a malicious storage device and pressing [mount] and getting breached. This is not a substitute for a thorough audit. This is not a substitute for lklfuse. This does not solve the general problem of in-kernel fs drivers being a huge attack surface. I just want a vacation from the sh*tstorm of bad ideas and threat models that I never agreed to support. v2: Add external logs to the list too, and document the var we set Signed-off-by: Darrick J. Wong Reviewed-by: Dave Chinner Reviewed-by: Carlos Maiolino --- configure.ac | 1 + include/builddefs.in | 2 ++ m4/package_services.m4 | 42 ++++++++++++++++++++++++++++++++++++++++++ scrub/Makefile | 11 +++++++++++ scrub/xfs.rules | 13 +++++++++++++ 5 files changed, 69 insertions(+) create mode 100644 scrub/xfs.rules diff --git a/configure.ac b/configure.ac index db1ca6292..517d0a3ad 100644 --- a/configure.ac +++ b/configure.ac @@ -209,6 +209,7 @@ AC_HAVE_SG_IO AC_HAVE_HDIO_GETGEO AC_CONFIG_SYSTEMD_SYSTEM_UNIT_DIR AC_CONFIG_CROND_DIR +AC_CONFIG_UDEV_RULE_DIR if test "$enable_blkid" = yes; then AC_HAVE_BLKID_TOPO diff --git a/include/builddefs.in b/include/builddefs.in index e0a2f3cbc..147c9b986 100644 --- a/include/builddefs.in +++ b/include/builddefs.in @@ -126,6 +126,8 @@ HAVE_SYSTEMD = @have_systemd@ SYSTEMD_SYSTEM_UNIT_DIR = @systemd_system_unit_dir@ HAVE_CROND = @have_crond@ CROND_DIR = @crond_dir@ +HAVE_UDEV = @have_udev@ +UDEV_RULE_DIR = @udev_rule_dir@ HAVE_LIBURCU_ATOMIC64 = @have_liburcu_atomic64@ GCCFLAGS = -funsigned-char -fno-strict-aliasing -Wall diff --git a/m4/package_services.m4 b/m4/package_services.m4 index f2d888a09..a683ddb93 100644 --- a/m4/package_services.m4 +++ b/m4/package_services.m4 @@ -75,3 +75,45 @@ AC_DEFUN([AC_CONFIG_CROND_DIR], AC_SUBST(have_crond) AC_SUBST(crond_dir) ]) + +# +# Figure out where to put udev rule files +# +AC_DEFUN([AC_CONFIG_UDEV_RULE_DIR], +[ + AC_REQUIRE([PKG_PROG_PKG_CONFIG]) + AC_ARG_WITH([udev_rule_dir], + [AS_HELP_STRING([--with-udev-rule-dir@<:@=DIR@:>@], + [Install udev rules into DIR.])], + [], + [with_udev_rule_dir=yes]) + AS_IF([test "x${with_udev_rule_dir}" != "xno"], + [ + AS_IF([test "x${with_udev_rule_dir}" = "xyes"], + [ + PKG_CHECK_MODULES([udev], [udev], + [ + with_udev_rule_dir="$($PKG_CONFIG --variable=udev_dir udev)/rules.d" + ], [ + with_udev_rule_dir="" + ]) + m4_pattern_allow([^PKG_(MAJOR|MINOR|BUILD|REVISION)$]) + ]) + AC_MSG_CHECKING([for udev rule dir]) + udev_rule_dir="${with_udev_rule_dir}" + AS_IF([test -n "${udev_rule_dir}"], + [ + AC_MSG_RESULT(${udev_rule_dir}) + have_udev="yes" + ], + [ + AC_MSG_RESULT(no) + have_udev="no" + ]) + ], + [ + have_udev="disabled" + ]) + AC_SUBST(have_udev) + AC_SUBST(udev_rule_dir) +]) diff --git a/scrub/Makefile b/scrub/Makefile index aba14ed23..4ad547178 100644 --- a/scrub/Makefile +++ b/scrub/Makefile @@ -28,6 +28,11 @@ endif endif # scrub_prereqs +UDEV_RULES = xfs.rules +ifeq ($(HAVE_UDEV),yes) + INSTALL_SCRUB += install-udev +endif + HFILES = \ common.h \ counter.h \ @@ -146,6 +151,12 @@ install-scrub: default $(LTINSTALL) -m 755 $(LTCOMMAND) $(PKG_SBIN_DIR) $(INSTALL) -m 755 $(XFS_SCRUB_ALL_PROG) $(PKG_SBIN_DIR) +install-udev: $(UDEV_RULES) + $(INSTALL) -m 755 -d $(UDEV_RULE_DIR) + for i in $(UDEV_RULES); do \ + $(INSTALL) -m 644 $$i $(UDEV_RULE_DIR)/64-$$i; \ + done + install-dev: -include .dep diff --git a/scrub/xfs.rules b/scrub/xfs.rules new file mode 100644 index 000000000..c3f69b3ab --- /dev/null +++ b/scrub/xfs.rules @@ -0,0 +1,13 @@ +# SPDX-License-Identifier: GPL-2.0-or-later +# +# Copyright (C) 2023 Oracle. All rights reserved. +# Author: Darrick J. Wong +# +# Don't let udisks automount XFS filesystems without even asking a user. +# This doesn't eliminate filesystems as an attack surface; it only prevents +# evil maid attacks when all sessions are locked. +# +# According to http://storaged.org/doc/udisks2-api/latest/udisks.8.html, +# supplying UDISKS_AUTO=0 here changes the HintAuto property of the block +# device abstraction to mean "do not automatically start" (e.g. mount). +SUBSYSTEM=="block", ENV{ID_FS_TYPE}=="xfs|xfs_external_log", ENV{UDISKS_AUTO}="0" -- 2.39.2