userns: user namespaces: convert all capable checks in kernel/sys.c

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.
	Feb 15: allow prlimit to current (was regression in previous version)
	Feb 23: remove debugging printks, uninline set_one_prio_perm and
		make it bool, and document its return value.
Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Daniel Lezcano <daniel.lezcano@free.fr>
Acked-by: David Howells <dhowells@redhat.com>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sys.c

@@ -119,17 +119,34 @@ EXPORT_SYMBOL(cad_pid);
 
 void (*pm_power_off_prepare)(void);
 
+/*
+ * Returns true if current's euid is same as p's uid or euid,
+ * or has CAP_SYS_NICE to p's user_ns.
+ *
+ * Called with rcu_read_lock, creds are safe
+ */
+static bool 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 true;
+	if (ns_capable(pcred->user->user_ns, CAP_SYS_NICE))
+		return true;
+	return false;
+}
+
 /*
  * 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;
 
-	if (pcred->uid  != cred->euid &&
-	    pcred->euid != cred->euid && !capable(CAP_SYS_NICE)) {
+	if (!set_one_prio_perm(p)) {
 		error = -EPERM;
 		goto out;
 	}
@@ -506,7 +523,7 @@ 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;
@@ -515,7 +532,7 @@ 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;
@@ -550,7 +567,7 @@ 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;
@@ -617,7 +634,7 @@ 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;
 	}
 
@@ -626,7 +643,7 @@ 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;
 	}
 
@@ -674,7 +691,7 @@ 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);
@@ -716,7 +733,7 @@ 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;
@@ -780,7 +797,7 @@ 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;
@@ -840,7 +857,7 @@ 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)
@@ -873,7 +890,7 @@ 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;
@@ -1183,6 +1200,7 @@ SYSCALL_DEFINE2(sethostname, char __user *, name, int, len)
 
 	if (!ns_capable(current->nsproxy->uts_ns->user_ns, CAP_SYS_ADMIN))
 		return -EPERM;
+
 	if (len < 0 || len > __NEW_UTS_LEN)
 		return -EINVAL;
 	down_write(&uts_sem);
@@ -1230,7 +1248,7 @@ 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;
@@ -1345,6 +1363,8 @@ 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;
@@ -1388,19 +1408,22 @@ static int check_prlimit_permission(struct task_struct *task)
 {
 	const struct cred *cred = current_cred(), *tcred;
 
-	tcred = __task_cred(task);
-	if (current != task &&
-	    (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;
-	}
+	if (current == task)
+		return 0;
 
-	return 0;
+	tcred = __task_cred(task);
+	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,