From: Oleg Nesterov <oleg@redhat.com> To: Christian Brauner <christian.brauner@ubuntu.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com>, linux-kernel@vger.kernel.org, Linux Containers <containers@lists.linux-foundation.org>, Christof Meerwald <cmeerw@cmeerw.org> Subject: Re: [PATCH] signal: Avoid corrupting si_pid and si_uid in do_notify_parent Date: Tue, 21 Apr 2020 13:11:40 +0200 Message-ID: <20200421111139.GC6787@redhat.com> (raw) In-Reply-To: <20200421102104.6pt34jknxmtu5ygm@wittgenstein> Sorry Christian, I don't understand... On 04/21, Christian Brauner wrote: > > On Tue, Apr 21, 2020 at 11:28:47AM +0200, Oleg Nesterov wrote: > > On 04/21, Christian Brauner wrote: > > > > > > > - __group_send_sig_info(sig, &info, tsk->parent); > > > > + __send_signal(sig, &info, tsk->parent, PIDTYPE_TGID, false); > > > > > > So below you switch to __send_signal() but set the "force" argument to > > > to "false". > > > > it must be false, the signal is generated from the parent's namespace or > > its descendant > > > > > Before that, if the signal was generated from another pid > > > namespace and we fixed up si_pid and si_uid the "force" argument was set > > > to "true", > > > > before that the "force" argument could be falsely true by the same reason, > > task_pid_nr_ns(tsk, tsk->parent) can return 0 because "tsk" no longer have > > pids after __unhash_process(). > > As I said in my mail, looking at the codepath it seems safe. My question > was whether it is _always_ incorrectly false which I do think it is Again, it must be always "false", it can be incorrectly "true" and this too is fixed by Eric's patch. > because child subreapers can't come from outside the pid namespace. If > they could you could create a scenario where the signal is generated > from a sibling pid namespace in which case it would be correctly set to > true. not sure I understand, but probably the answer is "yes"... task and task->parent either live in the same namespace or the child's namespace is the descendant of task->parent's namespace. In both cases task_pid_nr_ns(tsk, tsk->parent) should return the valid pid_nr and "force" must be false. The corner case is release_task() when the last exiting sub-thread sends a signal on behalf of its ->group_leader, and at this point all the tsk's pid pointers are NULL, that is why "force" can be falsely "true". Oleg.
next prev parent reply index Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-04-19 20:13 SIGCHLD signal sometimes sent with si_pid==0 (Linux 5.6.5) Christof Meerwald 2020-04-20 17:05 ` [PATCH] signal: Avoid corrupting si_pid and si_uid in do_notify_parent Eric W. Biederman 2020-04-21 8:30 ` Christian Brauner 2020-04-21 9:28 ` Oleg Nesterov 2020-04-21 10:21 ` Christian Brauner 2020-04-21 11:11 ` Oleg Nesterov [this message] 2020-04-21 11:26 ` Christian Brauner 2020-04-21 12:17 ` Oleg Nesterov 2020-04-21 12:59 ` Christian Brauner 2020-04-21 13:42 ` Eric W. Biederman 2020-04-21 11:28 ` Oleg Nesterov 2020-04-21 11:38 ` Christian Brauner 2020-04-21 10:28 ` Christian Brauner 2020-04-21 14:57 ` Eric W. Biederman 2020-04-21 15:08 ` Christian Brauner 2020-04-21 9:04 ` Oleg Nesterov 2020-04-21 10:19 ` [PATCH] remove the no longer needed pid_alive() check in __task_pid_nr_ns() Oleg Nesterov 2020-04-21 10:50 ` Christian Brauner 2020-04-21 15:05 ` Eric W. Biederman 2020-04-24 18:05 ` Oleg Nesterov 2020-04-24 19:54 ` Eric W. Biederman 2020-04-21 14:59 ` SIGCHLD signal sometimes sent with si_pid==0 (Linux 5.6.5) Eric W. Biederman
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