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.