[CRIU] [PATCH] security: check additional gids

[Ruslan Kuprieiev]

Currently, we only check if process gids match primary gid of user.
But user may have some additional groups. So lets check them too.

Signed-off-by: Ruslan Kuprieiev <kupruser at gmail.com>
---
  cr-service.c      |  3 ++-
  crtools.c         |  3 ++-
  include/crtools.h |  2 +-
  security.c        | 74 
+++++++++++++++++++++++++++++++++++++++++++++++--------
  4 files changed, 69 insertions(+), 13 deletions(-)

diff --git a/cr-service.c b/cr-service.c
index dc0ff5a..7802e71 100644
--- a/cr-service.c
+++ b/cr-service.c
@@ -178,7 +178,8 @@ static int setup_opts_from_req(int sk, CriuOpts *req)
          return -1;
      }

-    restrict_uid(ids.uid, ids.gid);
+    if (restrict_uid(ids.uid, ids.gid))
+        return -1;

      if (fstat(sk, &st)) {
          pr_perror("Can't get socket stat");
diff --git a/crtools.c b/crtools.c
index 5684186..96ae590 100644
--- a/crtools.c
+++ b/crtools.c
@@ -173,7 +173,8 @@ int main(int argc, char *argv[])
      BUILD_BUG_ON(PAGE_SIZE != PAGE_IMAGE_SIZE);

      cr_pb_init();
-    restrict_uid(getuid(), getgid());
+    if (restrict_uid(getuid(), getgid()))
+        return 1;

      if (argc < 2)
          goto usage;
diff --git a/include/crtools.h b/include/crtools.h
index c4ae580..75047fc 100644
--- a/include/crtools.h
+++ b/include/crtools.h
@@ -24,7 +24,7 @@ extern int cr_check(void);
  extern int cr_exec(int pid, char **opts);
  extern int cr_dedup(void);

-extern void restrict_uid(unsigned int uid, unsigned int gid);
+extern int restrict_uid(unsigned int uid, unsigned int gid);
  struct proc_status_creds;
  extern bool may_dump(struct proc_status_creds *);
  struct _CredsEntry;
diff --git a/security.c b/security.c
index d4b4230..3f3b73b 100644
--- a/security.c
+++ b/security.c
@@ -1,4 +1,9 @@
  #include <unistd.h>
+#include <pwd.h>
+#include <grp.h>
+#include <limits.h>
+#include <stdlib.h>
+
  #include "crtools.h"
  #include "proc_parse.h"
  #include "log.h"
@@ -8,7 +13,9 @@
  /*
   * UID and GID of user requesting for C/R
   */
-static unsigned int cr_uid, cr_gid;
+static unsigned int cr_uid;
+static unsigned int cr_gids[NGROUPS_MAX];
+static int cr_gids_num;

  /*
   * Setup what user is requesting for dump (via rpc or using
@@ -17,21 +24,68 @@ static unsigned int cr_uid, cr_gid;
   * access to. (Or implement some trickier security policy).
   */

-void restrict_uid(unsigned int uid, unsigned int gid)
+int restrict_uid(unsigned int uid, unsigned int gid)
  {
+    struct passwd *pwd;
+
      pr_info("Restrict C/R with %u:%u uid\n", uid, gid);
      cr_uid = uid;
-    cr_gid = gid;
+
+    pwd = getpwuid(uid);
+    if (!pwd) {
+        pr_perror("Can't get user name");
+        return -1;
+    }
+
+    cr_gids_num = NGROUPS_MAX;
+    if (getgrouplist(pwd->pw_name, gid, cr_gids, &cr_gids_num) < 0) {
+        pr_perror("Can't get group list of the user");
+        return -1;
+    }
+
+    return 0;
  }

-static bool check_ids(unsigned int crid, unsigned int rid, unsigned int 
eid, unsigned int sid)
+static bool check_uids(unsigned int crid, unsigned int rid, unsigned 
int eid, unsigned int sid)
  {
      if (crid == 0)
          return true;
      if (crid == rid && crid == eid && crid == sid)
          return true;

-    pr_err("UID/GID mismatch %u != (%u,%u,%u)\n", crid, rid, eid, sid);
+    pr_err("UID mismatch %u != (%u,%u,%u)\n", crid, rid, eid, sid);
+    return false;
+}
+
+static bool contains(unsigned int *crgids, unsigned int crgids_num, 
unsigned int gid)
+{
+    int i;
+
+    for (i = 0; i < crgids_num; ++i) {
+        if (crgids[i] == gid)
+            return true;
+    }
+
+    return false;
+}
+
+static bool check_gids(unsigned int cruid,
+              unsigned int *crgids,
+              unsigned int crgids_num,
+              unsigned int rid,
+              unsigned int eid,
+              unsigned int sid)
+{
+    if (contains(crgids, crgids_num, 0))
+        return true;
+
+    if (contains(crgids, crgids_num, rid) &&
+        contains(crgids, crgids_num, eid) &&
+        contains(crgids, crgids_num, sid))
+        return true;
+
+    pr_err("GID mismatch. User(uid %u, primary gid %u) is absent in 
(%u,%u,%u)",
+                      cruid, crgids[0], rid, eid, sid);
      return false;
  }

@@ -46,7 +100,7 @@ static bool check_caps(u32 *inh, u32 *eff, u32 *prm)
       * security model.
       */

-    if (cr_uid == 0 && cr_gid == 0)
+    if (cr_uid == 0 && contains(cr_gids, cr_gids_num, 0))
          return true;

      for (i = 0; i < CR_CAP_SIZE; i++) {
@@ -61,14 +115,14 @@ static bool check_caps(u32 *inh, u32 *eff, u32 *prm)

  bool may_dump(struct proc_status_creds *creds)
  {
-    return check_ids(cr_uid, creds->uids[0], creds->uids[1], 
creds->uids[2]) &&
-        check_ids(cr_gid, creds->gids[0], creds->gids[1], 
creds->gids[2]) &&
+    return check_uids(cr_uid, creds->uids[0], creds->uids[1], 
creds->uids[2]) &&
+        check_gids(cr_uid, cr_gids, cr_gids_num, creds->gids[0], 
creds->gids[1], creds->gids[2]) &&
          check_caps(creds->cap_inh, creds->cap_eff, creds->cap_prm);
  }

  bool may_restore(CredsEntry *creds)
  {
-    return check_ids(cr_uid, creds->uid, creds->euid, creds->suid) &&
-        check_ids(cr_gid, creds->gid, creds->egid, creds->sgid) &&
+    return check_uids(cr_uid, creds->uid, creds->euid, creds->suid) &&
+        check_gids(cr_uid, cr_gids, cr_gids_num, creds->gid, 
creds->egid, creds->sgid) &&
          check_caps(creds->cap_inh, creds->cap_eff, creds->cap_prm);
  }
-- 
1.8.3.2