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SubjectRe: [PATCH v2] signal: add procfd_signal() syscall
On Sat, Dec 01, 2018 at 09:28:47AM -0600, Eric W. Biederman wrote:
>
> It just occurs to me that the simple way to implement
> procfd_sigqueueinfo info is like:
>
> int copy_siginfo_from_user_any(kernel_siginfo_t *info, siginfo_t *uinfo)
> {
> #ifdef CONFIG_COMPAT
> if (in_compat_syscall)
> return copy_siginfo_from_user32(info, uinfo);

Right, though that would require a cast afaict.

static int __copy_siginfo_from_user_generic(int signo, kernel_siginfo_t *kinfo,
siginfo_t *info)
{
#ifdef CONFIG_COMPAT
if (in_compat_syscall())
return __copy_siginfo_from_user32(
signo, kinfo, (struct compat_siginfo __user *)info);
#endif
return __copy_siginfo_from_user(signo, kinfo, info);
}

It seems that a cast to (compat_siginfo __user *) should be safe in this
context? I've at least seen similar things done for __sys_sendmsg().

> #endif
> return copy_siginfo_from_user(info, uinfo);
> }
>
> long procfd_sigqueueinfo(int fd, siginfo_t *uinfo)

**bikeshedding**
Not a fan of that name. I'm going to go with procfd_send_signal().
sigqueue gives non-native speakers a lot of room for spelling errors and
it always seemed opaque to me what this function is doing without
consulting the manpage. :)

> {
> kernel_siginfo info;
>
> if (copy_siginfo_from_user_any(&info, uinfo))
> return -EFAULT;
> ...;
> }
>
> It looks like there is already a place in ptrace.c that already
> hand rolls copy_siginfo_from_user_any.
>
> So while I would love to figure out the subset of siginfo_t tha we can
> just pass through, as I think that would make a better more forward
> compatible copy_siginfo_from_user32. I think for this use case we just
> add the in_compat_syscall test and then we just need to ensure this new
> system call is placed in the proper places in the syscall table.
>
> Because we will need 3 call sights: x86_64, x32 and ia32. As the layout
> changes between those three subarchitecuters.
>
> Eric
>

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