[PATCH 06/08] user namespaces: convert all capable checks in kernel/sys.c

["Serge E. Hallyn" <serge@hallyn.com>]

This allows setuid/setgid in containers.  It also fixes some
corner cases where kernel logic foregoes capability checks when
uids are equivalent.  The latter will need to be done throughout
the whole kernel.

Changelog:
	Jan 11: Use nsown_capable() as suggested by Bastian Blank.
	Jan 11: Fix logic errors in uid checks pointed out by Bastian.

Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
---
 kernel/sys.c |   67 +++++++++++++++++++++++++++++++++++----------------------
 1 files changed, 41 insertions(+), 26 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index 9b9b03b..b68cd67 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -116,17 +116,29 @@ EXPORT_SYMBOL(cad_pid);
 
 void (*pm_power_off_prepare)(void);
 
+/* called with rcu_read_lock, creds are safe */
+static inline int set_one_prio_perm(struct task_struct *p)
+{
+	const struct cred *cred = current_cred(), *pcred = __task_cred(p);
+
+	if (pcred->user->user_ns == cred->user->user_ns &&
+	    (pcred->uid  == cred->euid ||
+	     pcred->euid == cred->euid))
+		return 1;
+	if (ns_capable(pcred->user->user_ns, CAP_SYS_NICE))
+		return 1;
+	return 0;
+}
+
 /*
  * set the priority of a task
  * - the caller must hold the RCU read lock
  */
 static int set_one_prio(struct task_struct *p, int niceval, int error)
 {
-	const struct cred *cred = current_cred(), *pcred = __task_cred(p);
-	int no_nice;
+	int ret, no_nice;
 
-	if (pcred->uid  != cred->euid &&
-	    pcred->euid != cred->euid && !capable(CAP_SYS_NICE)) {
+	if (!set_one_prio_perm(p)) {
 		error = -EPERM;
 		goto out;
 	}
@@ -496,7 +508,7 @@ SYSCALL_DEFINE2(setregid, gid_t, rgid, gid_t, egid)
 	if (rgid != (gid_t) -1) {
 		if (old->gid == rgid ||
 		    old->egid == rgid ||
-		    capable(CAP_SETGID))
+		    nsown_capable(CAP_SETGID))
 			new->gid = rgid;
 		else
 			goto error;
@@ -505,7 +517,7 @@ SYSCALL_DEFINE2(setregid, gid_t, rgid, gid_t, egid)
 		if (old->gid == egid ||
 		    old->egid == egid ||
 		    old->sgid == egid ||
-		    capable(CAP_SETGID))
+		    nsown_capable(CAP_SETGID))
 			new->egid = egid;
 		else
 			goto error;
@@ -540,7 +552,7 @@ SYSCALL_DEFINE1(setgid, gid_t, gid)
 	old = current_cred();
 
 	retval = -EPERM;
-	if (capable(CAP_SETGID))
+	if (nsown_capable(CAP_SETGID))
 		new->gid = new->egid = new->sgid = new->fsgid = gid;
 	else if (gid == old->gid || gid == old->sgid)
 		new->egid = new->fsgid = gid;
@@ -607,7 +619,7 @@ SYSCALL_DEFINE2(setreuid, uid_t, ruid, uid_t, euid)
 		new->uid = ruid;
 		if (old->uid != ruid &&
 		    old->euid != ruid &&
-		    !capable(CAP_SETUID))
+		    !nsown_capable(CAP_SETUID))
 			goto error;
 	}
 
@@ -616,7 +628,7 @@ SYSCALL_DEFINE2(setreuid, uid_t, ruid, uid_t, euid)
 		if (old->uid != euid &&
 		    old->euid != euid &&
 		    old->suid != euid &&
-		    !capable(CAP_SETUID))
+		    !nsown_capable(CAP_SETUID))
 			goto error;
 	}
 
@@ -664,7 +676,7 @@ SYSCALL_DEFINE1(setuid, uid_t, uid)
 	old = current_cred();
 
 	retval = -EPERM;
-	if (capable(CAP_SETUID)) {
+	if (nsown_capable(CAP_SETUID)) {
 		new->suid = new->uid = uid;
 		if (uid != old->uid) {
 			retval = set_user(new);
@@ -706,7 +718,7 @@ SYSCALL_DEFINE3(setresuid, uid_t, ruid, uid_t, euid, uid_t, suid)
 	old = current_cred();
 
 	retval = -EPERM;
-	if (!capable(CAP_SETUID)) {
+	if (!nsown_capable(CAP_SETUID)) {
 		if (ruid != (uid_t) -1 && ruid != old->uid &&
 		    ruid != old->euid  && ruid != old->suid)
 			goto error;
@@ -770,7 +782,7 @@ SYSCALL_DEFINE3(setresgid, gid_t, rgid, gid_t, egid, gid_t, sgid)
 	old = current_cred();
 
 	retval = -EPERM;
-	if (!capable(CAP_SETGID)) {
+	if (!nsown_capable(CAP_SETGID)) {
 		if (rgid != (gid_t) -1 && rgid != old->gid &&
 		    rgid != old->egid  && rgid != old->sgid)
 			goto error;
@@ -830,7 +842,7 @@ SYSCALL_DEFINE1(setfsuid, uid_t, uid)
 
 	if (uid == old->uid  || uid == old->euid  ||
 	    uid == old->suid || uid == old->fsuid ||
-	    capable(CAP_SETUID)) {
+	    nsown_capable(CAP_SETUID)) {
 		if (uid != old_fsuid) {
 			new->fsuid = uid;
 			if (security_task_fix_setuid(new, old, LSM_SETID_FS) == 0)
@@ -863,7 +875,7 @@ SYSCALL_DEFINE1(setfsgid, gid_t, gid)
 
 	if (gid == old->gid  || gid == old->egid  ||
 	    gid == old->sgid || gid == old->fsgid ||
-	    capable(CAP_SETGID)) {
+	    nsown_capable(CAP_SETGID)) {
 		if (gid != old_fsgid) {
 			new->fsgid = gid;
 			goto change_okay;
@@ -1220,7 +1232,7 @@ SYSCALL_DEFINE2(setdomainname, char __user *, name, int, len)
 	int errno;
 	char tmp[__NEW_UTS_LEN];
 
-	if (!capable(CAP_SYS_ADMIN))
+	if (!ns_capable(current->nsproxy->uts_ns->user_ns, CAP_SYS_ADMIN))
 		return -EPERM;
 	if (len < 0 || len > __NEW_UTS_LEN)
 		return -EINVAL;
@@ -1335,6 +1347,8 @@ int do_prlimit(struct task_struct *tsk, unsigned int resource,
 	rlim = tsk->signal->rlim + resource;
 	task_lock(tsk->group_leader);
 	if (new_rlim) {
+		/* Keep the capable check against init_user_ns until
+		   cgroups can contain all limits */
 		if (new_rlim->rlim_max > rlim->rlim_max &&
 				!capable(CAP_SYS_RESOURCE))
 			retval = -EPERM;
@@ -1379,17 +1393,18 @@ static int check_prlimit_permission(struct task_struct *task)
 	const struct cred *cred = current_cred(), *tcred;
 
 	tcred = __task_cred(task);
-	if ((cred->uid != tcred->euid ||
-	     cred->uid != tcred->suid ||
-	     cred->uid != tcred->uid  ||
-	     cred->gid != tcred->egid ||
-	     cred->gid != tcred->sgid ||
-	     cred->gid != tcred->gid) &&
-	     !capable(CAP_SYS_RESOURCE)) {
-		return -EPERM;
-	}
-
-	return 0;
+	if (cred->user->user_ns == tcred->user->user_ns &&
+	    (cred->uid == tcred->euid &&
+	     cred->uid == tcred->suid &&
+	     cred->uid == tcred->uid  &&
+	     cred->gid == tcred->egid &&
+	     cred->gid == tcred->sgid &&
+	     cred->gid == tcred->gid))
+		return 0;
+	if (ns_capable(tcred->user->user_ns, CAP_SYS_RESOURCE))
+		return 0;
+
+	return -EPERM;
 }
 
 SYSCALL_DEFINE4(prlimit64, pid_t, pid, unsigned int, resource,
-- 
1.7.0.4