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]> --- 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 _______________________________________________ Devel mailing list [email protected] https://openvz.org/mailman/listinfo/devel
