cgroup: cgroup.{procs,threads} factor out common parts

mainline inclusion
from mainline-v5.12-rc1
commit da70862e
bugzilla: 186050 https://gitee.com/openeuler/kernel/issues/I4DDEL
CVE: CVE-2021-4197

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=da70862efe0065bada33d67a903270cdbbaf07d9

--------------------------------

The functions cgroup_threads_write and cgroup_procs_write are almost
identical. In order to reduce duplication, factor out the common code in
similar fashion we already do for other threadgroup/task functions. No
functional changes are intended.
Suggested-by: NHao Lee <haolee.swjtu@gmail.com>
Signed-off-by: NMichal Koutný <mkoutny@suse.com>
Reviewed-by: NDaniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NLu Jialin <lujialin4@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

kernel/cgroup/cgroup.c

@@ -4835,8 +4835,8 @@ static int cgroup_attach_permissions(struct cgroup *src_cgrp,
 	return ret;
 }
 
-static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
-				  char *buf, size_t nbytes, loff_t off)
+static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
+				    bool threadgroup)
 {
 	struct cgroup *src_cgrp, *dst_cgrp;
 	struct task_struct *task;
@@ -4847,7 +4847,7 @@ static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
 	if (!dst_cgrp)
 		return -ENODEV;
 
-	task = cgroup_procs_write_start(buf, true, &locked);
+	task = cgroup_procs_write_start(buf, threadgroup, &locked);
 	ret = PTR_ERR_OR_ZERO(task);
 	if (ret)
 		goto out_unlock;
@@ -4857,19 +4857,26 @@ static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
 	src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
 	spin_unlock_irq(&css_set_lock);
 
+	/* process and thread migrations follow same delegation rule */
 	ret = cgroup_attach_permissions(src_cgrp, dst_cgrp,
-					of->file->f_path.dentry->d_sb, true);
+					of->file->f_path.dentry->d_sb, threadgroup);
 	if (ret)
 		goto out_finish;
 
-	ret = cgroup_attach_task(dst_cgrp, task, true);
+	ret = cgroup_attach_task(dst_cgrp, task, threadgroup);
 
 out_finish:
 	cgroup_procs_write_finish(task, locked);
 out_unlock:
 	cgroup_kn_unlock(of->kn);
 
-	return ret ?: nbytes;
+	return ret;
+}
+
+static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
+				  char *buf, size_t nbytes, loff_t off)
+{
+	return __cgroup_procs_write(of, buf, true) ?: nbytes;
 }
 
 static void *cgroup_threads_start(struct seq_file *s, loff_t *pos)
@@ -4880,41 +4887,7 @@ static void *cgroup_threads_start(struct seq_file *s, loff_t *pos)
 static ssize_t cgroup_threads_write(struct kernfs_open_file *of,
 				    char *buf, size_t nbytes, loff_t off)
 {
-	struct cgroup *src_cgrp, *dst_cgrp;
-	struct task_struct *task;
-	ssize_t ret;
-	bool locked;
-
-	buf = strstrip(buf);
-
-	dst_cgrp = cgroup_kn_lock_live(of->kn, false);
-	if (!dst_cgrp)
-		return -ENODEV;
-
-	task = cgroup_procs_write_start(buf, false, &locked);
-	ret = PTR_ERR_OR_ZERO(task);
-	if (ret)
-		goto out_unlock;
-
-	/* find the source cgroup */
-	spin_lock_irq(&css_set_lock);
-	src_cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
-	spin_unlock_irq(&css_set_lock);
-
-	/* thread migrations follow the cgroup.procs delegation rule */
-	ret = cgroup_attach_permissions(src_cgrp, dst_cgrp,
-					of->file->f_path.dentry->d_sb, false);
-	if (ret)
-		goto out_finish;
-
-	ret = cgroup_attach_task(dst_cgrp, task, false);
-
-out_finish:
-	cgroup_procs_write_finish(task, locked);
-out_unlock:
-	cgroup_kn_unlock(of->kn);
-
-	return ret ?: nbytes;
+	return __cgroup_procs_write(of, buf, false) ?: nbytes;
 }
 
 /* cgroup core interface files for the default hierarchy */