Re: CVS commit: src/sys/kern

[Rin Okuyama <rokuyama.rk%gmail.com@localhost>]

On 2020/11/04 22:52, Paul Goyette wrote:
> On Wed, 4 Nov 2020, Rin Okuyama wrote:
>
> > > ptrace_common_{init,fini} are called from the ptrace_common module's
> > > modcmd routine in kern/sys_ptrace_common.c.  The modcmd routine in
> > > turn is called at module initialization time.  In the case of a
> > > built-in module, it will be called by module_init via init_main; if
> > > the module is loaded (or auto-loaded) module_load will call the
> > > modcmd routine.
> > >
> > > The module will be built-in if either ``options PTRACE'' or ``file-
> > > system PROCFS'' is set in the kernel configuration file.
> >
> > Oops, sorry, I meant ptrace_{init,fini}(). These functions are not called
> > at all since this commit, which forbids ptrace(2) for non-root users.
>
> If the module is built-in (``options PTRACE'' selected in the config
> file), then the module will already have been initialized.
>
> If the module is not built-in, then a privileged user will need to
> modload(8) the module.
>
> Prior to this change, the built-in ptrace_common module was calling
> the ptrace module's init/fini routine.  Quite likely ptrace_common
> was built-in (due to inclusion of file-system PROCFS), so the init
> was handled during init_main().  This change ensures that the ptrace
> init/fini routines are called ONLY if the ptrace module itself (not
> the ptrace_common) routine is built-in.
>
> Please check to make sure that ``options PTRACE'' is included in
> your kernel config.

Yes:

$ config -x netbsd.gdb | grep PTRACE
###> options    PTRACE          # Include ptrace(2) syscall
###> options    PTRACE_HOOKS    # Include ptrace hooks

The problem is that ptrace_{init,fini}() are not called from
ptrace_modcmd():

https://nxr.netbsd.org/xref/src/sys/kern/sys_ptrace.c#184

    184 static int
    185 ptrace_modcmd(modcmd_t cmd, void *arg)
    186 {
    187 	int error;
    188
    189 	switch (cmd) {
    190 	case MODULE_CMD_INIT:
    191 		error = syscall_establish(&emul_netbsd, ptrace_syscalls);
    192 		break;
    193 	case MODULE_CMD_FINI:
    194 		error = syscall_disestablish(&emul_netbsd, ptrace_syscalls);
    195 		break;
    196 	default:
    197 		error = ENOTTY;
    198 		break;
    199 	}
    200 	return error;
    201 }

Can you easily confirm that ktrace(2) is unusable for non-privileged
users on 9.99.75 kernel:

$ gdb echo
GNU gdb (GDB) 8.3
...
(gdb) b main
Breakpoint 1 at 0x950: file /usr/src/bin/echo/echo.c, line 58.
(gdb) r
Starting program: /bin/echo
warning: Could not trace the inferior process.
Error:
warning: ptrace: Operation not permitted
terminate called after throwing an instance of 'gdb_exception_RETURN_MASK_ERROR'
[1]   Abort trap (core dumped) gdb echo

Also, ptrace_{init,fini} should be moved from sys_ptrace_common.c to
sys_ptrace.c, IMO.

Thanks,
rin