[Cc linux-api] On Thu 10-10-19 15:35:17, Christian Brauner wrote: > 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 <oleg@xxxxxxxxxx> > Cc: Florian Weimer <fweimer@xxxxxxxxxx> > Cc: libc-alpha@xxxxxxxxxxxxxx > Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx> > --- > include/uapi/linux/sched.h | 3 +++ > kernel/fork.c | 11 ++++++++++- > 2 files changed, 13 insertions(+), 1 deletion(-) > > 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..661f8d1f3881 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; > } > > @@ -2567,7 +2572,7 @@ 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) > + if (kargs->flags & ~(CLONE_LEGACY_FLAGS | CLONE3_CLEAR_SIGHAND)) > return false; > > /* > @@ -2577,6 +2582,10 @@ 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; > -- > 2.23.0 -- Michal Hocko SUSE Labs
