CHROMIUM: remove Android's cgroup generic permissions checks

The implementation is utterly broken, resulting in all processes being
allows to move tasks between sets (as long as they have access to the
"tasks" attribute), and upstream is heading towards checking only
capability anyway, so let's get rid of this code.

BUG=b:31790445,chromium:647994
TEST=Boot android container, examine logcat

Change-Id: I2f780a5992c34e52a8f2d0b3557fc9d490da2779
Signed-off-by: Dmitry Torokhov <dtor@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/394967
Reviewed-by: Ricky Zhou <rickyz@chromium.org>
Reviewed-by: John Stultz <john.stultz@linaro.org>

2 files changed, 2 insertions, 58 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index bd541053efc2..371ee5a827e0 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2663,45 +2663,6 @@ static int cgroup_attach_task(struct cgroup *dst_cgrp,
 	return ret;
 }
 
-int subsys_cgroup_allow_attach(struct cgroup_taskset *tset)
-{
-	const struct cred *cred = current_cred(), *tcred;
-	struct task_struct *task;
-	struct cgroup_subsys_state *css;
-
-	if (capable(CAP_SYS_NICE))
-		return 0;
-
-	cgroup_taskset_for_each(task, css, tset) {
-		tcred = __task_cred(task);
-
-		if (current != task && !uid_eq(cred->euid, tcred->uid) &&
-		    !uid_eq(cred->euid, tcred->suid))
-			return -EACCES;
-	}
-
-	return 0;
-}
-
-static int cgroup_allow_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
-{
-	struct cgroup_subsys_state *css;
-	int i;
-	int ret;
-
-	for_each_css(css, i, cgrp) {
-		if (css->ss->allow_attach) {
-			ret = css->ss->allow_attach(tset);
-			if (ret)
-				return ret;
-		} else {
-			return -EACCES;
-		}
-	}
-
-	return 0;
-}
-
 static int cgroup_procs_write_permission(struct task_struct *task,
 					 struct cgroup *dst_cgrp,
 					 struct kernfs_open_file *of)
@@ -2716,24 +2677,8 @@ static int cgroup_procs_write_permission(struct task_struct *task,
 	 */
 	if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
 	    !uid_eq(cred->euid, tcred->uid) &&
-	    !uid_eq(cred->euid, tcred->suid)) {
-		/*
-		 * if the default permission check fails, give each
-		 * cgroup a chance to extend the permission check
-		 */
-		struct cgroup_taskset tset = {
-			.src_csets = LIST_HEAD_INIT(tset.src_csets),
-			.dst_csets = LIST_HEAD_INIT(tset.dst_csets),
-			.csets = &tset.src_csets,
-		};
-		struct css_set *cset;
-		cset = task_css_set(task);
-		list_add(&cset->mg_node, &tset.src_csets);
-		ret = cgroup_allow_attach(dst_cgrp, &tset);
-		list_del(&tset.src_csets);
-		if (ret)
-			ret = -EACCES;
-	}
+	    !uid_eq(cred->euid, tcred->suid))
+		ret = -EACCES;
 
 	if (!ret && cgroup_on_dfl(dst_cgrp)) {
 		struct super_block *sb = of->file->f_path.dentry->d_sb;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c90bfb620981..471094bfbcc6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8935,7 +8935,6 @@ struct cgroup_subsys cpu_cgrp_subsys = {
 	.fork		= cpu_cgroup_fork,
 	.can_attach	= cpu_cgroup_can_attach,
 	.attach		= cpu_cgroup_attach,
-	.allow_attach   = subsys_cgroup_allow_attach,
 	.legacy_cftypes	= cpu_files,
 	.early_init	= 1,
 };