Quoting Oren Laadan ([email protected]): > Ghost (and dead) tasks exit as soon as they find their checkpoint_ctx. > That may occur before other tasks even enter sys_restart(). If a ghost > child dies before its child enters the syscall, the child will receive > the death_signal which is set by userspace (in non-container restart). > > This signal was supposedly skipped in reparent_thread() for restarting > task, but the PF_RESTARTING flag was tested on the child instead of > the parent; And the child was not in sys_restart, so .. bad luck. > > This patch fixes reparent_threads() to test the parent's flag instead. > > Also, if restart fails after some tasks have restore their state, then > the death_signal of such tasks is likely to have been reset. To ensure > proper cleanup in case of a failure, the coordinator tasks will force- > kill all those descendants whose checkpoint_ctx matches that of the > coordinator. > > (To avoid a potential security issue here, prepare_descendants() was > modified to only allow setting the checkpoint_task of a descendant if > the coordinator has PTRACE_MODE_ATTACH permissions over it). > > Signed-off-by: Oren Laadan <[email protected]>
Acked-by: Serge Hallyn <[email protected]> > --- > checkpoint/restart.c | 32 ++++++++++++++++++++++++++------ > kernel/exit.c | 2 +- > 2 files changed, 27 insertions(+), 7 deletions(-) > > diff --git a/checkpoint/restart.c b/checkpoint/restart.c > index c021eaf..258e9eb 100644 > --- a/checkpoint/restart.c > +++ b/checkpoint/restart.c > @@ -810,6 +810,11 @@ static int __prepare_descendants(struct task_struct > *task, void *data) > > ckpt_debug("consider task %d\n", task_pid_vnr(task)); > > + if (!ptrace_may_access(task, PTRACE_MODE_ATTACH)) { > + ckpt_debug("stranger task %d\n", task_pid_vnr(task)); > + return -EPERM; > + } > + > if (task_ptrace(task) & PT_PTRACED) { > ckpt_debug("ptraced task %d\n", task_pid_vnr(task)); > return -EBUSY; > @@ -935,6 +940,21 @@ static int init_restart_ctx(struct ckpt_ctx *ctx, pid_t > pid) > return 0; > } > > +static int __destroy_descendants(struct task_struct *task, void *data) > +{ > + struct ckpt_ctx *ctx = (struct ckpt_ctx *) data; > + > + if (task->checkpoint_ctx == ctx) > + force_sig(SIGKILL, task); > + > + return 0; > +} > + > +static void destroy_descendants(struct ckpt_ctx *ctx) > +{ > + walk_task_subtree(ctx->root_task, __destroy_descendants, ctx); > +} > + > static int do_restore_coord(struct ckpt_ctx *ctx, pid_t pid) > { > int ret; > @@ -972,8 +992,8 @@ static int do_restore_coord(struct ckpt_ctx *ctx, pid_t > pid) > > /* > * From now on we are committed to the restart. If anything > - * fails, we'll wipe out the entire subtree below us, to > - * ensure proper cleanup. > + * fails, we'll cleanup (that is, kill) those tasks in our > + * subtree that we marked for restart - see below. > */ > > if (ctx->uflags & RESTART_TASKSELF) { > @@ -1009,13 +1029,13 @@ static int do_restore_coord(struct ckpt_ctx *ctx, > pid_t pid) > ckpt_debug("freezing restart tasks ... %d\n", ret); > } > out: > - if (ret < 0) > + if (ret < 0) { > ckpt_set_ctx_error(ctx, ret); > - else > + destroy_descendants(ctx); > + } else { > ckpt_set_ctx_success(ctx); > - > - if (!(ctx->uflags & RESTART_TASKSELF)) > wake_up_all(&ctx->waitq); > + } > > set_task_ctx(current, NULL); > return ret; > diff --git a/kernel/exit.c b/kernel/exit.c > index 41ac4cf..cfb0f34 100644 > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -744,7 +744,7 @@ static void reparent_thread(struct task_struct *father, > struct task_struct *p, > struct list_head *dead) > { > /* restarting zombie doesn't trigger signals */ > - if (p->pdeath_signal && !(p->flags & PF_RESTARTING)) > + if (p->pdeath_signal && !(father->flags & PF_RESTARTING)) > group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p); > > list_move_tail(&p->sibling, &p->real_parent->children); > -- > 1.6.0.4 > > _______________________________________________ > Containers mailing list > [email protected] > https://lists.linux-foundation.org/mailman/listinfo/containers _______________________________________________ Containers mailing list [email protected] https://lists.linux-foundation.org/mailman/listinfo/containers _______________________________________________ Devel mailing list [email protected] https://openvz.org/mailman/listinfo/devel
