--- /dev/null
+From 16af238036a5464ae8f2420ed3af214f0de875f9 Mon Sep 17 00:00:00 2001
+From: Christian Brauner <christian.brauner@ubuntu.com>
+Date: Sat, 28 Jan 2017 13:02:34 +0100
+Subject: [PATCH] CVE-2017-5985: Ensure target netns is caller-owned
+
+Before this commit, lxc-user-nic could potentially have been tricked into
+operating on a network namespace over which the caller did not hold privilege.
+
+This commit ensures that the caller is privileged over the network namespace by
+temporarily dropping privilege.
+
+Launchpad: https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1654676
+Reported-by: Jann Horn <jannh@google.com>
+Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
+Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
+---
+ src/lxc/lxc_user_nic.c | 119 ++++++++++++++++++++++++++++++++++++-------------
+ 1 file changed, 87 insertions(+), 32 deletions(-)
+
+diff --git a/src/lxc/lxc_user_nic.c b/src/lxc/lxc_user_nic.c
+index 409a53a1..96dc3986 100644
+--- a/src/lxc/lxc_user_nic.c
++++ b/src/lxc/lxc_user_nic.c
+@@ -50,6 +50,14 @@
+ #include "utils.h"
+ #include "network.h"
+
++#define usernic_debug_stream(stream, format, ...) \
++ do { \
++ fprintf(stream, "%s: %d: %s: " format, __FILE__, __LINE__, \
++ __func__, __VA_ARGS__); \
++ } while (false)
++
++#define usernic_error(format, ...) usernic_debug_stream(stderr, format, __VA_ARGS__)
++
+ static void usage(char *me, bool fail)
+ {
+ fprintf(stderr, "Usage: %s lxcpath name pid type bridge nicname\n", me);
+@@ -670,68 +678,115 @@ again:
+ }
+
+ #define VETH_DEF_NAME "eth%d"
+-
+ static int rename_in_ns(int pid, char *oldname, char **newnamep)
+ {
+- int fd = -1, ofd = -1, ret, ifindex = -1;
++ uid_t ruid, suid, euid;
++ int fret = -1;
++ int fd = -1, ifindex = -1, ofd = -1, ret;
+ bool grab_newname = false;
+
+ ofd = lxc_preserve_ns(getpid(), "net");
+ if (ofd < 0) {
+- fprintf(stderr, "Failed opening network namespace path for '%d'.", getpid());
+- return -1;
++ usernic_error("Failed opening network namespace path for '%d'.", getpid());
++ return fret;
+ }
+
+ fd = lxc_preserve_ns(pid, "net");
+ if (fd < 0) {
+- fprintf(stderr, "Failed opening network namespace path for '%d'.", pid);
+- return -1;
++ usernic_error("Failed opening network namespace path for '%d'.", pid);
++ goto do_partial_cleanup;
++ }
++
++ ret = getresuid(&ruid, &euid, &suid);
++ if (ret < 0) {
++ usernic_error("Failed to retrieve real, effective, and saved "
++ "user IDs: %s\n",
++ strerror(errno));
++ goto do_partial_cleanup;
++ }
++
++ ret = setns(fd, CLONE_NEWNET);
++ close(fd);
++ fd = -1;
++ if (ret < 0) {
++ usernic_error("Failed to setns() to the network namespace of "
++ "the container with PID %d: %s.\n",
++ pid, strerror(errno));
++ goto do_partial_cleanup;
+ }
+
+- if (setns(fd, 0) < 0) {
+- fprintf(stderr, "setns to container network namespace\n");
+- goto out_err;
++ ret = setresuid(ruid, ruid, 0);
++ if (ret < 0) {
++ usernic_error("Failed to drop privilege by setting effective "
++ "user id and real user id to %d, and saved user "
++ "ID to 0: %s.\n",
++ ruid, strerror(errno));
++ // COMMENT(brauner): It's ok to jump to do_full_cleanup here
++ // since setresuid() will succeed when trying to set real,
++ // effective, and saved to values they currently have.
++ goto do_full_cleanup;
+ }
+- close(fd); fd = -1;
++
+ if (!*newnamep) {
+ grab_newname = true;
+ *newnamep = VETH_DEF_NAME;
+- if (!(ifindex = if_nametoindex(oldname))) {
+- fprintf(stderr, "failed to get netdev index\n");
+- goto out_err;
++
++ ifindex = if_nametoindex(oldname);
++ if (!ifindex) {
++ usernic_error("Failed to get netdev index: %s.\n", strerror(errno));
++ goto do_full_cleanup;
+ }
+ }
+- if ((ret = lxc_netdev_rename_by_name(oldname, *newnamep)) < 0) {
+- fprintf(stderr, "Error %d renaming netdev %s to %s in container\n", ret, oldname, *newnamep);
+- goto out_err;
++
++ ret = lxc_netdev_rename_by_name(oldname, *newnamep);
++ if (ret < 0) {
++ usernic_error("Error %d renaming netdev %s to %s in container.\n", ret, oldname, *newnamep);
++ goto do_full_cleanup;
+ }
++
+ if (grab_newname) {
+- char ifname[IFNAMSIZ], *namep = ifname;
++ char ifname[IFNAMSIZ];
++ char *namep = ifname;
++
+ if (!if_indextoname(ifindex, namep)) {
+- fprintf(stderr, "Failed to get new netdev name\n");
+- goto out_err;
++ usernic_error("Failed to get new netdev name: %s.\n", strerror(errno));
++ goto do_full_cleanup;
+ }
++
+ *newnamep = strdup(namep);
+ if (!*newnamep)
+- goto out_err;
++ goto do_full_cleanup;
+ }
+- if (setns(ofd, 0) < 0) {
+- fprintf(stderr, "Error returning to original netns\n");
+- close(ofd);
+- return -1;
++
++ fret = 0;
++
++do_full_cleanup:
++ ret = setresuid(ruid, euid, suid);
++ if (ret < 0) {
++ usernic_error("Failed to restore privilege by setting effective "
++ "user id to %d, real user id to %d, and saved user "
++ "ID to %d: %s.\n",
++ ruid, euid, suid, strerror(errno));
++ fret = -1;
++ // COMMENT(brauner): setns() should fail if setresuid() doesn't
++ // succeed but there's no harm in falling through; keeps the
++ // code cleaner.
+ }
+- close(ofd);
+
+- return 0;
++ ret = setns(ofd, CLONE_NEWNET);
++ if (ret < 0) {
++ usernic_error("Failed to setns() to original network namespace "
++ "of PID %d: %s.\n",
++ ofd, strerror(errno));
++ fret = -1;
++ }
+
+-out_err:
+- if (ofd >= 0)
+- close(ofd);
+- if (setns(ofd, 0) < 0)
+- fprintf(stderr, "Error returning to original network namespace\n");
++do_partial_cleanup:
+ if (fd >= 0)
+ close(fd);
+- return -1;
++ close(ofd);
++
++ return fret;
+ }
+
+ /*
+--
+2.11.0
+
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