[CRIU] [PATCH] security: check additional groups,v4

[Pavel Emelyanov]

On 07/08/2014 05:22 PM, Ruslan Kuprieiev wrote:
> Forgot to mention, I forgot to add "if (root) return true"  in 
> check_groups() in v3.
> 
> On 08.07.2014 16:18, Ruslan Kuprieiev wrote:
>> 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        | 99 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
>>   4 files changed, 99 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..d17c726 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 +68,61 @@ 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))) {

I still worry about cr_gid is not checked against rid, eid and sid. Are
you 100% sure that cr_groups will include one? Can we put the check here
for it being true?

>> +		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;
>> +
>> +	if (cr_gid == 0)
>> +		return true;
>> +
>> +	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 +150,14 @@ 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);
>>   }
> 
> .
>