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. Also include slight refactor to code removing possible new-line chars as per Yang Yang's work at [3]. This reduces code size and complexity by using more robust and better understood interfaces. Link: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings[1] Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2] Link: https://lore.kernel.org/all/202212091545310085328@xxxxxxxxxx/ [3] Link: https://github.com/KSPP/linux/issues/90 Cc: linux-hardening@xxxxxxxxxxxxxxx Co-developed-by: Yang Yang <yang.yang29@xxxxxxxxxx> Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx> --- Changes in v2: - use `sizeof` on destination string instead of `strlen` (thanks Andy, Kees and Dimitri) - refactor code to remove potential new-line chars (thanks Yang Yang and Andy) - Link to v1: https://lore.kernel.org/r/20230822-strncpy-arch-x86-platform-uv-uv_nmi-v1-1-931f2943de0d@xxxxxxxxxx --- Note: build-tested only Another thing, Yang Yang's patch [3] had some review from Andy regarding the use of `-1` and `+1` in and around the strnchrnul invocation. I believe Yang Yang's original implementation is correct but let's also just use sizeof(arg) instead of ACTION_LEN. Here's a godbolt link detailing some findings around the new-line refactor in response to Andy's feedback: https://godbolt.org/z/K8drG3oq5 --- arch/x86/platform/uv/uv_nmi.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/arch/x86/platform/uv/uv_nmi.c b/arch/x86/platform/uv/uv_nmi.c index a60af0230e27..913347b2b9ab 100644 --- a/arch/x86/platform/uv/uv_nmi.c +++ b/arch/x86/platform/uv/uv_nmi.c @@ -202,21 +202,17 @@ static int param_set_action(const char *val, const struct kernel_param *kp) { int i; int n = ARRAY_SIZE(valid_acts); - char arg[ACTION_LEN], *p; + char arg[ACTION_LEN]; /* (remove possible '\n') */ - strncpy(arg, val, ACTION_LEN - 1); - arg[ACTION_LEN - 1] = '\0'; - p = strchr(arg, '\n'); - if (p) - *p = '\0'; + strscpy(arg, val, strnchrnul(val, sizeof(arg) - 1, '\n') - val + 1); for (i = 0; i < n; i++) if (!strcmp(arg, valid_acts[i].action)) break; if (i < n) { - strcpy(uv_nmi_action, arg); + strscpy(uv_nmi_action, arg, sizeof(uv_nmi_action)); pr_info("UV: New NMI action:%s\n", uv_nmi_action); return 0; } @@ -959,7 +955,7 @@ static int uv_handle_nmi(unsigned int reason, struct pt_regs *regs) /* Unexpected return, revert action to "dump" */ if (master) - strncpy(uv_nmi_action, "dump", strlen(uv_nmi_action)); + strscpy(uv_nmi_action, "dump", sizeof(uv_nmi_action)); } /* Pause as all CPU's enter the NMI handler */ --- base-commit: 706a741595047797872e669b3101429ab8d378ef change-id: 20230822-strncpy-arch-x86-platform-uv-uv_nmi-474e5295c2c1 Best regards, -- Justin Stitt <justinstitt@xxxxxxxxxx>
