From: Eric W. Biederman ebiederm@xmission.com
commit 24f6008564183aa120d07c03d9289519c2fe02af upstream.
The cgroup release_agent is called with call_usermodehelper. The function call_usermodehelper starts the release_agent with a full set fo capabilities. Therefore require capabilities when setting the release_agaent.
Reported-by: Tabitha Sable tabitha.c.sable@gmail.com Tested-by: Tabitha Sable tabitha.c.sable@gmail.com Fixes: 81a6a5cdd2c5 ("Task Control Groups: automatic userspace notification of idle cgroups") Cc: stable@vger.kernel.org # v2.6.24+ Signed-off-by: "Eric W. Biederman" ebiederm@xmission.com Signed-off-by: Tejun Heo tj@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/cgroup/cgroup-v1.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)
--- a/kernel/cgroup/cgroup-v1.c +++ b/kernel/cgroup/cgroup-v1.c @@ -549,6 +549,14 @@ static ssize_t cgroup_release_agent_writ
BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
+ /* + * Release agent gets called with all capabilities, + * require capabilities to set release agent. + */ + if ((of->file->f_cred->user_ns != &init_user_ns) || + !capable(CAP_SYS_ADMIN)) + return -EPERM; + cgrp = cgroup_kn_lock_live(of->kn, false); if (!cgrp) return -ENODEV; @@ -961,6 +969,12 @@ int cgroup1_parse_param(struct fs_contex /* Specifying two release agents is forbidden */ if (ctx->release_agent) return cg_invalf(fc, "cgroup1: release_agent respecified"); + /* + * Release agent gets called with all capabilities, + * require capabilities to set release agent. + */ + if ((fc->user_ns != &init_user_ns) || !capable(CAP_SYS_ADMIN)) + return cg_invalf(fc, "cgroup1: Setting release_agent not allowed"); ctx->release_agent = param->string; param->string = NULL; break;