[CRIU] [PATCH] security: check additional groups,v3

[Ruslan Kuprieiev]

Currently, we only check if process gids match primary gid of user.
But process and user have additional groups too. So lets:
     1) check that process rgid,egid and sgid are in the user's grouplist.
     2) on restore check that user has all groups from the images.

Signed-off-by: Ruslan Kuprieiev <kupruser at gmail.com>
---
 cr-service.c      |  3 +-
 crtools.c         |  3 +-
 include/crtools.h |  2 +-
 security.c        | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
 4 files changed, 96 insertions(+), 8 deletions(-)

diff --git a/cr-service.c b/cr-service.c
index 64ce751..9504c14 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 b662fff..28d343e 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..253f674 100644
--- a/security.c
+++ b/security.c
@@ -1,14 +1,22 @@
 #include <unistd.h>
+#include <pwd.h>
+#include <grp.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+
 #include "crtools.h"
 #include "proc_parse.h"
 #include "log.h"
+#include "xmalloc.h"
 
 #include "protobuf/creds.pb-c.h"
 
 /*
- * UID and GID of user requesting for C/R
+ * UID, GID and groups of user requesting for C/R
  */
 static unsigned int cr_uid, cr_gid;
+static unsigned int cr_ngroups, *cr_groups;
 
 /*
  * Setup what user is requesting for dump (via rpc or using
@@ -17,11 +25,36 @@ 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)
 {
-	pr_info("Restrict C/R with %u:%u uid\n", uid, gid);
+	struct passwd *pwd;
+	unsigned int buf[NGROUPS_MAX];
+	int nbuf;
+
+	pr_info("Restrict C/R with %u:%u uid:gid\n", uid, gid);
 	cr_uid = uid;
 	cr_gid = gid;
+
+	pwd = getpwuid(uid);
+	if (!pwd) {
+		pr_perror("Can't get password file entry");
+		return -1;
+	}
+
+	nbuf = NGROUPS_MAX;
+	if (getgrouplist(pwd->pw_name, pwd->pw_gid, buf, &nbuf) < 0) {
+		pr_perror("Can't get group list");
+		return -1;
+	}
+
+	cr_ngroups = nbuf;
+	cr_groups = xmalloc(cr_ngroups*sizeof(*cr_groups));
+	if (!cr_groups)
+		return -1;
+
+	memcpy(cr_groups, buf, cr_ngroups*sizeof(*cr_groups));
+
+	return 0;
 }
 
 static bool check_ids(unsigned int crid, unsigned int rid, unsigned int eid, unsigned int sid)
@@ -35,6 +68,58 @@ static bool check_ids(unsigned int crid, unsigned int rid, unsigned int eid, uns
 	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 rid, unsigned int eid, unsigned int sid)
+{
+	if (cr_gid == 0)
+		return true;
+
+	if (!(contains(cr_groups, cr_ngroups, rid) &&
+	    contains(cr_groups, cr_ngroups, eid)  &&
+	    contains(cr_groups, cr_ngroups, sid))) {
+		pr_err("GID mismatch. User is absent in (%u,%u,%u)",
+							rid, eid, sid);
+		return false;
+	}
+
+	return true;
+}
+
+/*
+ * There is no need to check groups on dump, because if uids and gids match
+ * then groups will match too. Btw, getting groups on dump is problematic.
+ * We can't parse proc, as it contains only first 32 groups. And we can't use
+ * getgrouplist, as it reads /etc/group which depends on the namespace.
+ *
+ * On restore we're getting groups from imgs and can check if user didn't add
+ * wrong groups by modifying images.
+ */
+static bool check_groups(unsigned int *groups, unsigned int ngroups)
+{
+	int i;
+
+	for (i = 0; i < ngroups; ++i) {
+		if (!contains(cr_groups, cr_ngroups, groups[i])) {
+			pr_err("GID mismatch. User is absent in %u group\n",
+								groups[i]);
+			return false;
+		}
+	}
+
+	return true;
+}
+
 static bool check_caps(u32 *inh, u32 *eff, u32 *prm)
 {
 	int i;
@@ -62,13 +147,14 @@ 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]) &&
+		check_gids(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) &&
+		check_gids(creds->gid, creds->egid, creds->sgid) &&
+		check_groups(creds->groups, creds->n_groups) &&
 		check_caps(creds->cap_inh, creds->cap_eff, creds->cap_prm);
 }
-- 
1.8.3.2