From patchwork Fri Oct 11 10:25:36 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Brauner X-Patchwork-Id: 34915 Received: (qmail 99787 invoked by alias); 11 Oct 2019 10:25:51 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 99670 invoked by uid 89); 11 Oct 2019 10:25:51 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-20.6 required=5.0 tests=AWL, BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, KAM_SHORT autolearn=ham version=3.3.1 spammy= X-HELO: youngberry.canonical.com From: Christian Brauner To: linux-kernel@vger.kernel.org, Oleg Nesterov , Florian Weimer , libc-alpha@sourceware.org Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Shuah Khan , Andrew Morton , Michal Hocko , Elena Reshetova , Thomas Gleixner , Roman Gushchin , Andrea Arcangeli , Al Viro , Aleksa Sarai , "Dmitry V. Levin" , linux-kselftest@vger.kernel.org, Christian Brauner , linux-api@vger.kernel.org Subject: [PATCH v2 1/2] clone3: add CLONE3_CLEAR_SIGHAND Date: Fri, 11 Oct 2019 12:25:36 +0200 Message-Id: <20191011102537.27502-1-christian.brauner@ubuntu.com> MIME-Version: 1.0 Reset all signal handlers of the child not set to SIG_IGN to SIG_DFL. Mutually exclusive with CLONE_SIGHAND to not disturb other thread's signal handler. In the spirit of closer cooperation between glibc developers and kernel developers (cf. [2]) this patchset came out of a discussion on the glibc mailing list for improving posix_spawn() (cf. [1], [3], [4]). Kernel support for this feature has been explicitly requested by glibc and I see no reason not to help them with this. The child helper process on Linux posix_spawn must ensure that no signal handlers are enabled, so the signal disposition must be either SIG_DFL or SIG_IGN. However, it requires a sigprocmask to obtain the current signal mask and at least _NSIG sigaction calls to reset the signal handlers for each posix_spawn call or complex state tracking that might lead to data corruption in glibc. Adding this flags lets glibc avoid these problems. [1]: https://www.sourceware.org/ml/libc-alpha/2019-10/msg00149.html [3]: https://www.sourceware.org/ml/libc-alpha/2019-10/msg00158.html [4]: https://www.sourceware.org/ml/libc-alpha/2019-10/msg00160.html [2]: https://lwn.net/Articles/799331/ '[...] by asking for better cooperation with the C-library projects in general. They should be copied on patches containing ABI changes, for example. I noted that there are often times where C-library developers wish the kernel community had done things differently; how could those be avoided in the future? Members of the audience suggested that more glibc developers should perhaps join the linux-api list. The other suggestion was to "copy Florian on everything".' Cc: Oleg Nesterov Cc: Florian Weimer Cc: libc-alpha@sourceware.org Cc: linux-api@vger.kernel.org Signed-off-by: Christian Brauner --- /* v1 */ Link: https://lore.kernel.org/r/20191010133518.5420-1-christian.brauner@ubuntu.com /* v2 */ - Florian Weimer : - update comment in clone3_args_valid() --- include/uapi/linux/sched.h | 3 +++ kernel/fork.c | 16 +++++++++++----- 2 files changed, 14 insertions(+), 5 deletions(-) diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h index 99335e1f4a27..c583720f689f 100644 --- a/include/uapi/linux/sched.h +++ b/include/uapi/linux/sched.h @@ -33,6 +33,9 @@ #define CLONE_NEWNET 0x40000000 /* New network namespace */ #define CLONE_IO 0x80000000 /* Clone io context */ +/* Flags for the clone3() syscall */ +#define CLONE3_CLEAR_SIGHAND 0x100000000ULL /* Clear any signal handler and reset to SIG_DFL. */ + #ifndef __ASSEMBLY__ /** * struct clone_args - arguments for the clone3 syscall diff --git a/kernel/fork.c b/kernel/fork.c index 1f6c45f6a734..0a0269cb2c18 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1517,6 +1517,11 @@ static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk) spin_lock_irq(¤t->sighand->siglock); memcpy(sig->action, current->sighand->action, sizeof(sig->action)); spin_unlock_irq(¤t->sighand->siglock); + + /* Reset all signal handler not set to SIG_IGN to SIG_DFL. */ + if (clone_flags & CLONE3_CLEAR_SIGHAND) + flush_signal_handlers(tsk, 0); + return 0; } @@ -2563,11 +2568,8 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs, static bool clone3_args_valid(const struct kernel_clone_args *kargs) { - /* - * All lower bits of the flag word are taken. - * Verify that no other unknown flags are passed along. - */ - if (kargs->flags & ~CLONE_LEGACY_FLAGS) + /* Verify that no unknown flags are passed along. */ + if (kargs->flags & ~(CLONE_LEGACY_FLAGS | CLONE3_CLEAR_SIGHAND)) return false; /* @@ -2577,6 +2579,10 @@ static bool clone3_args_valid(const struct kernel_clone_args *kargs) if (kargs->flags & (CLONE_DETACHED | CSIGNAL)) return false; + if ((kargs->flags & (CLONE_SIGHAND | CLONE3_CLEAR_SIGHAND)) == + (CLONE_SIGHAND | CLONE3_CLEAR_SIGHAND)) + return false; + if ((kargs->flags & (CLONE_THREAD | CLONE_PARENT)) && kargs->exit_signal) return false;