cherry-pick CVE-2018-6556 fix

from upstream's stable-3.0 branch

debian/patches/extra/0013-CVE-2018-6556-verify-netns-fd-in-lxc-user-nic.patch

@@ -0,0 +1,115 @@
+From 590b215c4f5225cfb7fb58d9c56fabd5197bfdac Mon Sep 17 00:00:00 2001
+From: Christian Brauner <christian.brauner@ubuntu.com>
+Date: Wed, 25 Jul 2018 19:56:54 +0200
+Subject: [PATCH] CVE 2018-6556: verify netns fd in lxc-user-nic
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
+(cherry picked from commit c1cf54ebf251fdbad1e971679614e81649f1c032)
+Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
+---
+ src/lxc/utils.h            |  5 +++++
+ src/lxc/cmd/lxc_user_nic.c | 35 ++++++++++++++++++++++++++++++++---
+ src/lxc/utils.c            | 12 ++++++++++++
+ 3 files changed, 49 insertions(+), 3 deletions(-)
+
+diff --git a/src/lxc/utils.h b/src/lxc/utils.h
+index ed486853..4dff26ae 100644
+--- a/src/lxc/utils.h
++++ b/src/lxc/utils.h
+@@ -95,6 +95,10 @@
+ #define CGROUP2_SUPER_MAGIC 0x63677270
+ #endif
+ 
++#ifndef NSFS_MAGIC
++#define NSFS_MAGIC 0x6e736673
++#endif
++
+ /* Useful macros */
+ /* Maximum number for 64 bit integer is a string with 21 digits: 2^64 - 1 = 21 */
+ #define LXC_NUMSTRLEN64 21
+@@ -580,6 +584,7 @@ extern void *must_realloc(void *orig, size_t sz);
+ /* __typeof__ should be safe to use with all compilers. */
+ typedef __typeof__(((struct statfs *)NULL)->f_type) fs_type_magic;
+ extern bool has_fs_type(const char *path, fs_type_magic magic_val);
++extern bool fhas_fs_type(int fd, fs_type_magic magic_val);
+ extern bool is_fs_type(const struct statfs *fs, fs_type_magic magic_val);
+ extern bool lxc_nic_exists(char *nic);
+ extern int lxc_make_tmpfile(char *template, bool rm);
+diff --git a/src/lxc/cmd/lxc_user_nic.c b/src/lxc/cmd/lxc_user_nic.c
+index ec9cd97e..c5beb6c8 100644
+--- a/src/lxc/cmd/lxc_user_nic.c
++++ b/src/lxc/cmd/lxc_user_nic.c
+@@ -1179,12 +1179,41 @@ int main(int argc, char *argv[])
+ 			exit(EXIT_FAILURE);
+ 		}
+ 	} else if (request == LXC_USERNIC_DELETE) {
+-		netns_fd = open(args.pid, O_RDONLY);
++		char opath[LXC_PROC_PID_FD_LEN];
++
++		/* Open the path with O_PATH which will not trigger an actual
++		 * open(). Don't report an errno to the caller to not leak
++		 * information whether the path exists or not.
++		 * When stracing setuid is stripped so this is not a concern
++		 * either.
++		 */
++		netns_fd = open(args.pid, O_PATH | O_CLOEXEC);
+ 		if (netns_fd < 0) {
+-			usernic_error("Could not open \"%s\": %s\n", args.pid,
+-				      strerror(errno));
++			usernic_error("Failed to open \"%s\"\n", args.pid);
++			exit(EXIT_FAILURE);
++		}
++
++		if (!fhas_fs_type(netns_fd, NSFS_MAGIC)) {
++			usernic_error("Path \"%s\" does not refer to a network namespace path\n", args.pid);
++			close(netns_fd);
++			exit(EXIT_FAILURE);
++		}
++
++		ret = snprintf(opath, sizeof(opath), "/proc/self/fd/%d", netns_fd);
++		if (ret < 0 || (size_t)ret >= sizeof(opath)) {
++			close(netns_fd);
++			exit(EXIT_FAILURE);
++		}
++
++		/* Now get an fd that we can use in setns() calls. */
++		ret = open(opath, O_RDONLY | O_CLOEXEC);
++		if (ret < 0) {
++			usernic_error("Failed to open \"%s\": %s\n", args.pid, strerror(errno));
++			close(netns_fd);
+ 			exit(EXIT_FAILURE);
+ 		}
++		close(netns_fd);
++		netns_fd = ret;
+ 	}
+ 
+ 	if (!create_db_dir(LXC_USERNIC_DB)) {
+diff --git a/src/lxc/utils.c b/src/lxc/utils.c
+index 9771b900..e6f600f9 100644
+--- a/src/lxc/utils.c
++++ b/src/lxc/utils.c
+@@ -2551,6 +2551,18 @@ bool has_fs_type(const char *path, fs_type_magic magic_val)
+ 	return has_type;
+ }
+ 
++bool fhas_fs_type(int fd, fs_type_magic magic_val)
++{
++	int ret;
++	struct statfs sb;
++
++	ret = fstatfs(fd, &sb);
++	if (ret < 0)
++		return false;
++
++	return is_fs_type(&sb, magic_val);
++}
++
+ bool lxc_nic_exists(char *nic)
+ {
+ #define __LXC_SYS_CLASS_NET_LEN 15 + IFNAMSIZ + 1
+-- 
+2.18.0
+

debian/patches/series

@@ -18,3 +18,4 @@ extra/0009-apparmor-update-current-profiles.patch
 extra/0010-apparmor-profile-generation.patch
 extra/0011-apparmor-allow-start-container-to-change-to-lxc.patch
 extra/0012-tests-add-test-for-generated-apparmor-profiles.patch
+extra/0013-CVE-2018-6556-verify-netns-fd-in-lxc-user-nic.patch