On Thu, Mar 19, 2009 at 04:16:15PM -0500, Serge E. Hallyn wrote: > In a kernel compiled with CONFIG_USER_SCHED=y, cpu shares are > allocated according to uid. Shares are specifiable under > /sys/kernel/uids/<uid>/ > > In a kernel compiled with CONFIG_USER_NS=y, clone(2) with the > CLONE_NEWUSER flag creates a new user namespace, and the newly > cloned task will belong to uid 0 in the new user namespace. > > Without this patch, if uid 500 calls clone(CLONE_NEWUSER) (which > is possible using a program with the cap_sys_admin,cap_setuid,cap_setgid=pe > file capabilities), then the new task will get the cpu shares of > uid 0. > > After this patch, if uid 500 calls clone(CLONE_NEWUSER), then even > though it is uid 0 in the new user namespace, it will be restricted to > the cpu shares of uid 500. > > Currently there is no way to set shares for uids in user namespaces > other than the initial one. That will be trivial to add when > sysfs tagging (or its functional equivalent, also needed to > expose network devices in network namespaces other than init) > becomes available. > > Until cross-user-namespace file accesses are enforced, nothing > stops uid 0 in a child namespace from simply writing new values > into /sys/kernel/uids/500. > > Here are results of some testing with and without the patch. > > Cpu shares are initialized as follows:: > user root: 2048 > user hallyn: 1024 > user serge: 512 > > Results are the 'real' part of time make -j4 > o 2>&1, > each time after a make clean. > > ================================================================= > UNPATCHED > User 1: user serge creates a child user_ns and runs as user root > User 2: hallyn runs as user hallyn > ================================================================= > User 1 User 2 > run 1: 2m58.834s 3m0.609s > run 2: 2m59.248s 2m59.457s > > ============================================================= > PATCHED > User 1: user serge > User 2: user hallyn > ============================================================= > > User 1 User 2 > run 1: 3m6.337s 2m22.681s > run 2: 3m6.323s 2m21.855s > > ============================================================= > PATCHED > User 1: user serge setuid to user root > User 2: hallyn > ============================================================= > > User 1 User 2 > run 1: 2m17.782s 3m3.947s > run 2: 2m18.497s 3m7.961s > > ========================================================== > PATCHED > User 1: user root inside userns created by userid serge > User 2: hallyn > ========================================================== > > User 1 User 2 > run 1: 3m9.876s 2m8.428s > run 2: 3m8.539s 2m6.356s > > Signed-off-by: Serge E. Hallyn <serue@xxxxxxxxxx> > Signed-off-by: Dhaval Giani <dhaval@xxxxxxxxxxxxxxxxxx> > Cc: mingo@xxxxxxx > Cc: Bharata B Rao <bharata@xxxxxxxxxxxxxxxxxx> > Cc: peterz@xxxxxxxxxxxxx > --- > kernel/user.c | 12 +++++++++--- > kernel/user_namespace.c | 2 +- > 2 files changed, 10 insertions(+), 4 deletions(-) > > diff --git a/kernel/user.c b/kernel/user.c > index 850e0ba..53aeea2 100644 > --- a/kernel/user.c > +++ b/kernel/user.c > @@ -101,7 +101,12 @@ static int sched_create_user(struct user_struct *up) > { > int rc = 0; > > - up->tg = sched_create_group(&root_task_group); > + struct task_group *parent = &root_task_group; > + > + if (up->user_ns != &init_user_ns) > + parent = up->user_ns->creator->tg; > + > + up->tg = sched_create_group(parent); > if (IS_ERR(up->tg)) > rc = -ENOMEM; > > @@ -434,11 +439,11 @@ struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid) > new->uid = uid; > atomic_set(&new->__count, 1); > > + new->user_ns = get_user_ns(ns); > + > if (sched_create_user(new) < 0) > goto out_free_user; > > - new->user_ns = get_user_ns(ns); > - > if (uids_user_create(new)) > goto out_destoy_sched; > > @@ -472,6 +477,7 @@ out_destoy_sched: > sched_destroy_user(new); > put_user_ns(new->user_ns); Shouldn't this put_user_ns(new->user_ns) be removed? It looks like two references to new->user_ns are being dropped if anything fails after sched_create_user(new) succeeds yet as far as I can tell the patch does not introduce any new references to new->user_ns. Otherwise looks good to me. Cheers, -Matt Helsley _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers