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

   1 From 590b215c4f5225cfb7fb58d9c56fabd5197bfdac Mon Sep 17 00:00:00 2001
   2 From: Christian Brauner <christian.brauner@ubuntu.com>
   3 Date: Wed, 25 Jul 2018 19:56:54 +0200
   4 Subject: [PATCH] CVE 2018-6556: verify netns fd in lxc-user-nic
   5 MIME-Version: 1.0
   6 Content-Type: text/plain; charset=UTF-8
   7 Content-Transfer-Encoding: 8bit
   8
   9 Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
  10 (cherry picked from commit c1cf54ebf251fdbad1e971679614e81649f1c032)
  11 Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
  12 ---
  13  src/lxc/utils.h            |  5 +++++
  14  src/lxc/cmd/lxc_user_nic.c | 35 ++++++++++++++++++++++++++++++++---
  15  src/lxc/utils.c            | 12 ++++++++++++
  16  3 files changed, 49 insertions(+), 3 deletions(-)
  17
  18 diff --git a/src/lxc/utils.h b/src/lxc/utils.h
  19 index ed486853..4dff26ae 100644
  20 --- a/src/lxc/utils.h
  21 +++ b/src/lxc/utils.h
  22 @@ -95,6 +95,10 @@
  23  #define CGROUP2_SUPER_MAGIC 0x63677270
  24  #endif
  25
  26 +#ifndef NSFS_MAGIC
  27 +#define NSFS_MAGIC 0x6e736673
  28 +#endif
  29 +
  30  /* Useful macros */
  31  /* Maximum number for 64 bit integer is a string with 21 digits: 2^64 - 1 = 21 */
  32  #define LXC_NUMSTRLEN64 21
  33 @@ -580,6 +584,7 @@ extern void *must_realloc(void *orig, size_t sz);
  34  /* __typeof__ should be safe to use with all compilers. */
  35  typedef __typeof__(((struct statfs *)NULL)->f_type) fs_type_magic;
  36  extern bool has_fs_type(const char *path, fs_type_magic magic_val);
  37 +extern bool fhas_fs_type(int fd, fs_type_magic magic_val);
  38  extern bool is_fs_type(const struct statfs *fs, fs_type_magic magic_val);
  39  extern bool lxc_nic_exists(char *nic);
  40  extern int lxc_make_tmpfile(char *template, bool rm);
  41 diff --git a/src/lxc/cmd/lxc_user_nic.c b/src/lxc/cmd/lxc_user_nic.c
  42 index ec9cd97e..c5beb6c8 100644
  43 --- a/src/lxc/cmd/lxc_user_nic.c
  44 +++ b/src/lxc/cmd/lxc_user_nic.c
  45 @@ -1179,12 +1179,41 @@ int main(int argc, char *argv[])
  46                         exit(EXIT_FAILURE);
  47                 }
  48         } else if (request == LXC_USERNIC_DELETE) {
  49 -               netns_fd = open(args.pid, O_RDONLY);
  50 +               char opath[LXC_PROC_PID_FD_LEN];
  51 +
  52 +               /* Open the path with O_PATH which will not trigger an actual
  53 +                * open(). Don't report an errno to the caller to not leak
  54 +                * information whether the path exists or not.
  55 +                * When stracing setuid is stripped so this is not a concern
  56 +                * either.
  57 +                */
  58 +               netns_fd = open(args.pid, O_PATH | O_CLOEXEC);
  59                 if (netns_fd < 0) {
  60 -                       usernic_error("Could not open \"%s\": %s\n", args.pid,
  61 -                                     strerror(errno));
  62 +                       usernic_error("Failed to open \"%s\"\n", args.pid);
  63 +                       exit(EXIT_FAILURE);
  64 +               }
  65 +
  66 +               if (!fhas_fs_type(netns_fd, NSFS_MAGIC)) {
  67 +                       usernic_error("Path \"%s\" does not refer to a network namespace path\n", args.pid);
  68 +                       close(netns_fd);
  69 +                       exit(EXIT_FAILURE);
  70 +               }
  71 +
  72 +               ret = snprintf(opath, sizeof(opath), "/proc/self/fd/%d", netns_fd);
  73 +               if (ret < 0 || (size_t)ret >= sizeof(opath)) {
  74 +                       close(netns_fd);
  75 +                       exit(EXIT_FAILURE);
  76 +               }
  77 +
  78 +               /* Now get an fd that we can use in setns() calls. */
  79 +               ret = open(opath, O_RDONLY | O_CLOEXEC);
  80 +               if (ret < 0) {
  81 +                       usernic_error("Failed to open \"%s\": %s\n", args.pid, strerror(errno));
  82 +                       close(netns_fd);
  83                         exit(EXIT_FAILURE);
  84                 }
  85 +               close(netns_fd);
  86 +               netns_fd = ret;
  87         }
  88
  89         if (!create_db_dir(LXC_USERNIC_DB)) {
  90 diff --git a/src/lxc/utils.c b/src/lxc/utils.c
  91 index 9771b900..e6f600f9 100644
  92 --- a/src/lxc/utils.c
  93 +++ b/src/lxc/utils.c
  94 @@ -2551,6 +2551,18 @@ bool has_fs_type(const char *path, fs_type_magic magic_val)
  95         return has_type;
  96  }
  97
  98 +bool fhas_fs_type(int fd, fs_type_magic magic_val)
  99 +{
 100 +       int ret;
 101 +       struct statfs sb;
 102 +
 103 +       ret = fstatfs(fd, &sb);
 104 +       if (ret < 0)
 105 +               return false;
 106 +
 107 +       return is_fs_type(&sb, magic_val);
 108 +}
 109 +
 110  bool lxc_nic_exists(char *nic)
 111  {
 112  #define __LXC_SYS_CLASS_NET_LEN 15 + IFNAMSIZ + 1
 113 --
 114 2.18.0
 115