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lxc: add patch (fixes #8629)

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Piraty 2019-02-13 22:42:00 +01:00 committed by Helmut Pozimski
parent 27e4b7ef6d
commit 7f27191c6c
2 changed files with 150 additions and 1 deletions
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148
srcpkgs/lxc/patches/rexecute.patch Normal file
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@ -0,0 +1,148 @@
From d3a9befc86113228f77c89030336faa84a5557c0 Mon Sep 17 00:00:00 2001
From: Christian Brauner <christian.brauner@ubuntu.com>
Date: Tue, 12 Feb 2019 17:31:14 +0100
Subject: [PATCH] rexec: make rexecution opt-in for library callers
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
We cannot rexecute the liblxc shared library unconditionally as this would
break most of our downstreams. Here are some scenarios:
- anyone performing a dlopen() on the shared library (e.g. users of the LXC
Python bindings)
- LXD as it needs to know the absolute path to its own executable based on
/proc/self/exe etc.
This commit makes the rexecution of liblxc conditional on whether the
LXC_MEMFD_REXEC environment variable is set or not. If it is then liblxc is
unconditionally rexecuted.
The only relevant attack vector exists for lxc-attach which we simply reexecute
unconditionally.
Reported-by: Stéphane Graber <stgraber@ubuntu.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
src/lxc/Makefile.am | 4 +++-
src/lxc/rexec.c | 4 ++--
src/lxc/rexec.h | 26 ++++++++++++++++++++++++++
src/lxc/tools/lxc_attach.c | 18 ++++++++++++++++++
4 files changed, 49 insertions(+), 3 deletions(-)
create mode 100644 src/lxc/rexec.h
diff --git a/src/lxc/Makefile.am b/src/lxc/Makefile.am
index e1499a7eb..ef19df9e0 100644
--- src/lxc/Makefile.am
+++ src/lxc/Makefile.am
@@ -25,6 +25,7 @@ noinst_HEADERS = api_extensions.h \
monitor.h \
namespace.h \
raw_syscalls.h \
+ rexec.h \
start.h \
state.h \
storage/btrfs.h \
@@ -180,7 +181,7 @@ liblxc_la_SOURCES += ../include/strlcat.c ../include/strlcat.h
endif
if ENFORCE_MEMFD_REXEC
-liblxc_la_SOURCES += rexec.c
+liblxc_la_SOURCES += rexec.c rexec.h
endif
AM_CFLAGS = -DLXCROOTFSMOUNT=\"$(LXCROOTFSMOUNT)\" \
@@ -307,6 +308,7 @@ LDADD = liblxc.la \
if ENABLE_TOOLS
lxc_attach_SOURCES = tools/lxc_attach.c \
+ rexec.c rexec.h \
tools/arguments.c tools/arguments.h
lxc_autostart_SOURCES = tools/lxc_autostart.c \
tools/arguments.c tools/arguments.h
diff --git a/src/lxc/rexec.c b/src/lxc/rexec.c
index 3ce499b1e..024728d85 100644
--- src/lxc/rexec.c
+++ src/lxc/rexec.c
@@ -142,7 +142,7 @@ static void lxc_rexec_as_memfd(char **argv, char **envp, const char *memfd_name)
errno = saved_errno;
}
-static int lxc_rexec(const char *memfd_name)
+int lxc_rexec(const char *memfd_name)
{
int ret;
char **argv = NULL, **envp = NULL;
@@ -179,7 +179,7 @@ static int lxc_rexec(const char *memfd_name)
*/
__attribute__((constructor)) static void liblxc_rexec(void)
{
- if (lxc_rexec("liblxc")) {
+ if (getenv("LXC_MEMFD_REXEC") && lxc_rexec("liblxc")) {
fprintf(stderr, "Failed to re-execute liblxc via memory file descriptor\n");
_exit(EXIT_FAILURE);
}
diff --git a/src/lxc/rexec.h b/src/lxc/rexec.h
new file mode 100644
index 000000000..088ded932
--- /dev/null
+++ src/lxc/rexec.h
@@ -0,0 +1,26 @@
+/* liblxcapi
+ *
+ * Copyright © 2019 Christian Brauner <christian.brauner@ubuntu.com>.
+ * Copyright © 2019 Canonical Ltd.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef __LXC_REXEC_H
+#define __LXC_REXEC_H
+
+extern int lxc_rexec(const char *memfd_name);
+
+#endif /* __LXC_REXEC_H */
diff --git a/src/lxc/tools/lxc_attach.c b/src/lxc/tools/lxc_attach.c
index 3de0d7747..d10b6ecc2 100644
--- src/lxc/tools/lxc_attach.c
+++ src/lxc/tools/lxc_attach.c
@@ -44,10 +44,28 @@
#include "config.h"
#include "confile.h"
#include "log.h"
+#include "rexec.h"
#include "utils.h"
lxc_log_define(lxc_attach, lxc);
+/**
+ * This function will copy any binary that calls liblxc into a memory file and
+ * will use the memfd to rexecute the binary. This is done to prevent attacks
+ * through the /proc/self/exe symlink to corrupt the host binary when host and
+ * container are in the same user namespace or have set up an identity id
+ * mapping: CVE-2019-5736.
+ */
+#ifdef ENFORCE_MEMFD_REXEC
+__attribute__((constructor)) static void lxc_attach_rexec(void)
+{
+ if (!getenv("LXC_MEMFD_REXEC") && lxc_rexec("lxc-attach")) {
+ fprintf(stderr, "Failed to re-execute lxc-attach via memory file descriptor\n");
+ _exit(EXIT_FAILURE);
+ }
+}
+#endif
+
static int my_parser(struct lxc_arguments *args, int c, char *arg);
static int add_to_simple_array(char ***array, ssize_t *capacity, char *value);
static bool stdfd_is_pty(void);

3
srcpkgs/lxc/template
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@ -3,7 +3,7 @@ _desc="Linux Containers"
pkgname=lxc
version=3.0.3
revision=3
revision=4
build_style=gnu-configure
configure_args="--enable-doc --enable-seccomp
--enable-capabilities --enable-apparmor --with-distro=none
@ -54,5 +54,6 @@ lxc-devel_package() {
vmove usr/include
vmove usr/lib/pkgconfig
vmove "usr/lib/*.so"
vmove "usr/lib/*.a"
}
}