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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id j12sm6494689pjw.52.2021.06.25.20.42.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Jun 2021 20:42:07 -0700 (PDT) Date: Fri, 25 Jun 2021 20:42:06 -0700 From: Kees Cook To: "Eric W. Biederman" Cc: Linus Torvalds , Al Viro , Michael Schmitz , linux-arch , Jens Axboe , Oleg Nesterov , Linux Kernel Mailing List , Richard Henderson , Ivan Kokshaysky , Matt Turner , alpha , Geert Uytterhoeven , linux-m68k , Arnd Bergmann , Tejun Heo Subject: Re: [PATCH 6/9] signal: Fold do_group_exit into get_signal fixing io_uring threads Message-ID: <202106252038.389B963B6F@keescook> References: <87a6njf0ia.fsf@disp2133> <87tulpbp19.fsf@disp2133> <87zgvgabw1.fsf@disp2133> <875yy3850g.fsf_-_@disp2133> <874kdn6q87.fsf_-_@disp2133> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <874kdn6q87.fsf_-_@disp2133> Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Thu, Jun 24, 2021 at 02:02:16PM -0500, Eric W. Biederman wrote: > > Forld do_group_exit into get_signal as it is the last caller. > > Move the group_exit logic above the PF_IO_WORKER exit, ensuring > that if an PF_IO_WORKER catches SIGKILL every thread in > the thread group will exit not just the the PF_IO_WORKER. > > Now that the information is easily available only set PF_SIGNALED > when it was a signal that caused the exit. > > Signed-off-by: "Eric W. Biederman" > --- > include/linux/sched/task.h | 1 - > kernel/exit.c | 31 ------------------------------- > kernel/signal.c | 35 +++++++++++++++++++++++++---------- > 3 files changed, 25 insertions(+), 42 deletions(-) > > diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h > index ef02be869cf2..45525512e3d0 100644 > --- a/include/linux/sched/task.h > +++ b/include/linux/sched/task.h > @@ -77,7 +77,6 @@ static inline void exit_thread(struct task_struct *tsk) > { > } > #endif > -extern void do_group_exit(int); > > extern void exit_files(struct task_struct *); > extern void exit_itimers(struct signal_struct *); > diff --git a/kernel/exit.c b/kernel/exit.c > index 921519d80b56..635f434122b7 100644 > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -892,37 +892,6 @@ SYSCALL_DEFINE1(exit, int, error_code) > do_exit((error_code&0xff)<<8); > } > > -/* > - * Take down every thread in the group. This is called by fatal signals > - * as well as by sys_exit_group (below). > - */ > -void > -do_group_exit(int exit_code) > -{ > - struct signal_struct *sig = current->signal; > - > - BUG_ON(exit_code & 0x80); /* core dumps don't get here */ > - > - if (signal_group_exit(sig)) > - exit_code = sig->group_exit_code; > - else if (!thread_group_empty(current)) { > - struct sighand_struct *const sighand = current->sighand; > - > - spin_lock_irq(&sighand->siglock); > - if (signal_group_exit(sig)) > - /* Another thread got here before we took the lock. */ > - exit_code = sig->group_exit_code; > - else { > - sig->group_exit_code = exit_code; > - sig->flags = SIGNAL_GROUP_EXIT; > - zap_other_threads(current); Oh, now I see it: the "new code" in start_group_exit() is an open-coded zap_other_threads()? That wasn't clear to me, but makes sense now. > - } > - spin_unlock_irq(&sighand->siglock); > - } > - > - do_exit(exit_code); > - /* NOTREACHED */ > -} > > /* > * this kills every thread in the thread group. Note that any externally > diff --git a/kernel/signal.c b/kernel/signal.c > index c79c010ca5f3..95a076af600a 100644 > --- a/kernel/signal.c > +++ b/kernel/signal.c > @@ -2646,6 +2646,7 @@ bool get_signal(struct ksignal *ksig) > { > struct sighand_struct *sighand = current->sighand; > struct signal_struct *signal = current->signal; > + int exit_code; > int signr; > > if (unlikely(current->task_works)) > @@ -2848,8 +2849,6 @@ bool get_signal(struct ksignal *ksig) > /* > * Anything else is fatal, maybe with a core dump. > */ > - current->flags |= PF_SIGNALED; > - > if (sig_kernel_coredump(signr)) { > if (print_fatal_signals) > print_fatal_signal(ksig->info.si_signo); > @@ -2857,14 +2856,33 @@ bool get_signal(struct ksignal *ksig) > /* > * If it was able to dump core, this kills all > * other threads in the group and synchronizes with > - * their demise. If we lost the race with another > - * thread getting here, it set group_exit_code > - * first and our do_group_exit call below will use > - * that value and ignore the one we pass it. > + * their demise. If another thread makes it > + * to do_coredump first, it will set group_exit_code > + * which will be passed to do_exit. > */ > do_coredump(&ksig->info); > } > > + /* > + * Death signals, no core dump. > + */ > + exit_code = signr; > + if (signal_group_exit(signal)) { > + exit_code = signal->group_exit_code; > + } else { > + spin_lock_irq(&sighand->siglock); > + if (signal_group_exit(signal)) { > + /* Another thread got here before we took the lock. */ > + exit_code = signal->group_exit_code; > + } else { > + start_group_exit_locked(signal, exit_code); And here's the "if we didn't already do start_group_exit(), do it here". And that state is entirely captured via the SIGNAL_GROUP_EXIT flag. Cool. > + } > + spin_unlock_irq(&sighand->siglock); > + } > + > + if (exit_code & 0x7f) > + current->flags |= PF_SIGNALED; > + > /* > * PF_IO_WORKER threads will catch and exit on fatal signals > * themselves. They have cleanup that must be performed, so > @@ -2873,10 +2891,7 @@ bool get_signal(struct ksignal *ksig) > if (current->flags & PF_IO_WORKER) > goto out; > > - /* > - * Death signals, no core dump. > - */ > - do_group_exit(ksig->info.si_signo); > + do_exit(exit_code); > /* NOTREACHED */ > } > spin_unlock_irq(&sighand->siglock); > -- > 2.20.1 > -- Kees Cook