On Wed, Aug 23, 2023 at 04:00:13PM -0700, Kees Cook wrote: > On Wed, Aug 23, 2023 at 03:49:34PM -0700, Justin Stitt wrote: > > On Wed, Aug 23, 2023 at 4:07 AM Andy Shevchenko > > <andy.shevchenko@xxxxxxxxx> wrote: > > > > > > On Wed, Aug 23, 2023 at 1:32 AM Justin Stitt <justinstitt@xxxxxxxxxx> wrote: > > > > > > > > Both `strncpy` and `strcpy` are deprecated for use on NUL-terminated > > > > destination strings [1]. > > > > > > > > A suitable replacement is `strscpy` [2] due to the fact that it > > > > guarantees NUL-termination on its destination buffer argument which is > > > > _not_ the case for `strncpy` or `strcpy`! > > > > > > > > In this case, we can drop both the forced NUL-termination and the `... -1` from: > > > > | strncpy(arg, val, ACTION_LEN - 1); > > > > as `strscpy` implicitly has this behavior. > > > > > > ... > > > > > > > char arg[ACTION_LEN], *p; > > > > > > > > /* (remove possible '\n') */ > > > > - strncpy(arg, val, ACTION_LEN - 1); > > > > - arg[ACTION_LEN - 1] = '\0'; > > > > + strscpy(arg, val, ACTION_LEN); > > > > p = strchr(arg, '\n'); > > > > if (p) > > > > *p = '\0'; > > > > > > https://lore.kernel.org/all/202212091545310085328@xxxxxxxxxx/ > > > > > > ... > > > > > > > + strscpy(uv_nmi_action, arg, strlen(uv_nmi_action)); > > > > > > strlen() on the destination?! The original code for the above (strcpy()), copies strlen(arg) assuming null termination, so strlen(uv_nmi_action) is not correct for this case. You probably want to use sizeof of the destination. > > > > > > ... > > > > > > > - strncpy(uv_nmi_action, "dump", strlen(uv_nmi_action)); > > > > + strscpy(uv_nmi_action, "dump", strlen(uv_nmi_action)); > > > > > > Again, this is weird. > > > > This is a common pattern with `strxcpy` and `sizeof` if you `$ rg > > "strncpy\(.*sizeof"`. Do you recommend I switch the strlen(dest) to > > strlen(src)? I only kept as-is because that's what was there > > originally and I assumed some greater purpose of it. > > It's best to avoid any assumptions. If it can't be answered through code > inspection, the next best thing would be to ask for clarification. In > looking I see uv_nmi_action is a string: > > arch/x86/platform/uv/uv_nmi.c:193:typedef char action_t[ACTION_LEN]; > > arch/x86/platform/uv/uv_nmi.c: strcpy(uv_nmi_action, arg); > arch/x86/platform/uv/uv_nmi.c:module_param_named(action, uv_nmi_action, action, 0644); > arch/x86/platform/uv/uv_nmi.c: return (strncmp(uv_nmi_action, action, strlen(action)) == 0); > arch/x86/platform/uv/uv_nmi.c: strncpy(uv_nmi_action, "dump", strlen(uv_nmi_action)); > > using strlen() here seems "accidentally safe", as it's overwriting > "kdump": > > if (uv_nmi_action_is("kdump")) { > uv_nmi_kdump(cpu, master, regs); > > /* Unexpected return, revert action to "dump" */ > if (master) > strncpy(uv_nmi_action, "dump", strlen(uv_nmi_action)); > > anyway, a simple "sizeof" should be used AFAICT. > I agree.
