From 181104628653c6c66c9c3bb5b937153987228e63 Mon Sep 17 00:00:00 2001 From: Colin Cross Date: Tue, 12 Jul 2011 19:53:24 -0700 Subject: [PATCH] cgroup: Add generic cgroup subsystem permission checks Rather than using explicit euid == 0 checks when trying to move tasks into a cgroup via CFS, move permission checks into each specific cgroup subsystem. If a subsystem does not specify a 'allow_attach' handler, then we fall back to doing our checks the old way. Use the 'allow_attach' handler for the 'cpu' cgroup to allow non-root processes to add arbitrary processes to a 'cpu' cgroup if it has the CAP_SYS_NICE capability set. This version of the patch adds a 'allow_attach' handler instead of reusing the 'can_attach' handler. If the 'can_attach' handler is reused, a new cgroup that implements 'can_attach' but not the permission checks could end up with no permission checks at all. Change-Id: Icfa950aa9321d1ceba362061d32dc7dfa2c64f0c Original-Author: San Mehat Signed-off-by: Colin Cross --- Documentation/cgroups/cgroups.txt | 9 ++++++++ include/linux/cgroup-defs.h | 2 ++ kernel/cgroup.c | 38 +++++++++++++++++++++++++++++-- 3 files changed, 47 insertions(+), 2 deletions(-) diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt index c6256ae9885b..2d984e20783b 100644 --- a/Documentation/cgroups/cgroups.txt +++ b/Documentation/cgroups/cgroups.txt @@ -578,6 +578,15 @@ is completely unused; @cgrp->parent is still valid. (Note - can also be called for a newly-created cgroup if an error occurs after this subsystem's create() method has been called for the new cgroup). +int allow_attach(struct cgroup *cgrp, struct cgroup_taskset *tset) +(cgroup_mutex held by caller) + +Called prior to moving a task into a cgroup; if the subsystem +returns an error, this will abort the attach operation. Used +to extend the permission checks - if all subsystems in a cgroup +return 0, the attach will be allowed to proceed, even if the +default permission check (root or same user) fails. + int can_attach(struct cgroup *cgrp, struct cgroup_taskset *tset) (cgroup_mutex held by caller) diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index 06b77f9dd3f2..f3425da070e1 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -422,6 +422,8 @@ struct cgroup_subsys { void (*css_reset)(struct cgroup_subsys_state *css); void (*css_e_css_changed)(struct cgroup_subsys_state *css); + int (*allow_attach)(struct cgroup_subsys_state *css, + struct cgroup_taskset *tset); int (*can_attach)(struct cgroup_taskset *tset); void (*cancel_attach)(struct cgroup_taskset *tset); void (*attach)(struct cgroup_taskset *tset); diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 35591b841db2..de6515d19279 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2682,6 +2682,25 @@ int subsys_cgroup_allow_attach(struct cgroup_subsys_state *css, struct cgroup_ta 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(css, 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) @@ -2696,8 +2715,23 @@ 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)) - ret = -EACCES; + !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); + if (ret) + ret = -EACCES; + } if (!ret && cgroup_on_dfl(dst_cgrp)) { struct super_block *sb = of->file->f_path.dentry->d_sb; -- 2.34.1