The core codepaths to check whether a process can be attached to a cgroup are the same for threads and thread-group leaders. Only a small piece of code verifying that source and destination cgroup are in the same domain differentiates the thread permission checking from thread-group leader permission checking. Since cgroup_migrate_vet_dst() only matters cgroup2 - it is a noop on cgroup1 - we can move it out of cgroup_attach_task(). All checks can now be consolidated into a new helper cgroup_attach_permissions() callable from both cgroup_procs_write() and cgroup_threads_write(). Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: Li Zefan <lizefan@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: cgroups@xxxxxxxxxxxxxxx Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx> --- /* v1 */ Link: https://lore.kernel.org/r/20191218173516.7875-2-christian.brauner@xxxxxxxxxx /* v2 */ Link: https://lore.kernel.org/r/20191223061504.28716-2-christian.brauner@xxxxxxxxxx - Christian Brauner <christian.brauner@xxxxxxxxxx>: - Fix return value of cgroup_attach_permissions. It used to return 0 when it should've returned -EOPNOTSUPP. - Fix call to cgroup_attach_permissions() in cgroup_procs_write(). It accidently specified that a thread was moved causing an additional check for domain-group equality to be executed that is not needed. /* v3 */ Link: https://lore.kernel.org/r/20200117002143.15559-2-christian.brauner@xxxxxxxxxx unchanged /* v4 */ unchanged --- kernel/cgroup/cgroup.c | 46 +++++++++++++++++++++++++++++------------- 1 file changed, 32 insertions(+), 14 deletions(-) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 735af8f15f95..ad1f9fea5c14 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -2719,11 +2719,7 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader, { DEFINE_CGROUP_MGCTX(mgctx); struct task_struct *task; - int ret; - - ret = cgroup_migrate_vet_dst(dst_cgrp); - if (ret) - return ret; + int ret = 0; /* look up all src csets */ spin_lock_irq(&css_set_lock); @@ -4690,6 +4686,33 @@ static int cgroup_procs_write_permission(struct cgroup *src_cgrp, return 0; } +static inline bool cgroup_same_domain(const struct cgroup *src_cgrp, + const struct cgroup *dst_cgrp) +{ + return src_cgrp->dom_cgrp == dst_cgrp->dom_cgrp; +} + +static int cgroup_attach_permissions(struct cgroup *src_cgrp, + struct cgroup *dst_cgrp, + struct super_block *sb, bool thread) +{ + int ret = 0; + + ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp, sb); + if (ret) + return ret; + + ret = cgroup_migrate_vet_dst(dst_cgrp); + if (ret) + return ret; + + if (thread && + !cgroup_same_domain(src_cgrp->dom_cgrp, dst_cgrp->dom_cgrp)) + ret = -EOPNOTSUPP; + + return ret; +} + static ssize_t cgroup_procs_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off) { @@ -4712,8 +4735,8 @@ 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); - ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp, - of->file->f_path.dentry->d_sb); + ret = cgroup_attach_permissions(src_cgrp, dst_cgrp, + of->file->f_path.dentry->d_sb, false); if (ret) goto out_finish; @@ -4757,16 +4780,11 @@ static ssize_t cgroup_threads_write(struct kernfs_open_file *of, spin_unlock_irq(&css_set_lock); /* thread migrations follow the cgroup.procs delegation rule */ - ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp, - of->file->f_path.dentry->d_sb); + ret = cgroup_attach_permissions(src_cgrp, dst_cgrp, + of->file->f_path.dentry->d_sb, true); if (ret) goto out_finish; - /* and must be contained in the same domain */ - ret = -EOPNOTSUPP; - if (src_cgrp->dom_cgrp != dst_cgrp->dom_cgrp) - goto out_finish; - ret = cgroup_attach_task(dst_cgrp, task, false); out_finish: -- 2.25.0
