| Message ID | 20230911-strncpy-arch-x86-xen-efi-c-v1-1-96ab2bba2feb@google.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 1e9b56f53f8acd9fa594e9109108af5f03bcd1ff |
| Headers | show |
| Series | xen/efi: refactor deprecated strncpy | expand |
On Mon, Sep 11, 2023 at 06:59:31PM +0000, Justin Stitt wrote: > `strncpy` is deprecated for use on NUL-terminated destination strings [1]. > > `efi_loader_signature` has space for 4 bytes. We are copying "Xen" (3 bytes) > plus a NUL-byte which makes 4 total bytes. With that being said, there is > currently not a bug with the current `strncpy()` implementation in terms of > buffer overreads but we should favor a more robust string interface > either way. Yeah, this will work. Since this is a u32 destination, I do wonder if strtomem_pad() would be better since we're not really writing a string? But since this is all hard-coded, it doesn't matter. :) Reviewed-by: Kees Cook <keescook@chromium.org> -Kees > > A suitable replacement is `strscpy` [2] due to the fact that it guarantees > NUL-termination on the destination buffer while being functionally the > same in this case. > > 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://github.com/KSPP/linux/issues/90 > Cc: linux-hardening@vger.kernel.org > Cc: Kees Cook <keescook@chromium.org> > Signed-off-by: Justin Stitt <justinstitt@google.com> > --- > Note: build-tested > --- > arch/x86/xen/efi.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/xen/efi.c b/arch/x86/xen/efi.c > index 863d0d6b3edc..7250d0e0e1a9 100644 > --- a/arch/x86/xen/efi.c > +++ b/arch/x86/xen/efi.c > @@ -138,7 +138,7 @@ void __init xen_efi_init(struct boot_params *boot_params) > if (efi_systab_xen == NULL) > return; > > - strncpy((char *)&boot_params->efi_info.efi_loader_signature, "Xen", > + strscpy((char *)&boot_params->efi_info.efi_loader_signature, "Xen", > sizeof(boot_params->efi_info.efi_loader_signature)); > boot_params->efi_info.efi_systab = (__u32)__pa(efi_systab_xen); > boot_params->efi_info.efi_systab_hi = (__u32)(__pa(efi_systab_xen) >> 32); > > --- > base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c > change-id: 20230911-strncpy-arch-x86-xen-efi-c-14292f5a79ee > > Best regards, > -- > Justin Stitt <justinstitt@google.com> >
On 11.09.23 20:59, Justin Stitt wrote: > `strncpy` is deprecated for use on NUL-terminated destination strings [1]. > > `efi_loader_signature` has space for 4 bytes. We are copying "Xen" (3 bytes) > plus a NUL-byte which makes 4 total bytes. With that being said, there is > currently not a bug with the current `strncpy()` implementation in terms of > buffer overreads but we should favor a more robust string interface > either way. > > A suitable replacement is `strscpy` [2] due to the fact that it guarantees > NUL-termination on the destination buffer while being functionally the > same in this case. > > 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://github.com/KSPP/linux/issues/90 > Cc: linux-hardening@vger.kernel.org > Cc: Kees Cook <keescook@chromium.org> > Signed-off-by: Justin Stitt <justinstitt@google.com> Pushed to xen/tip.git for-linus-6.6a Juergen
diff --git a/arch/x86/xen/efi.c b/arch/x86/xen/efi.c index 863d0d6b3edc..7250d0e0e1a9 100644 --- a/arch/x86/xen/efi.c +++ b/arch/x86/xen/efi.c @@ -138,7 +138,7 @@ void __init xen_efi_init(struct boot_params *boot_params) if (efi_systab_xen == NULL) return; - strncpy((char *)&boot_params->efi_info.efi_loader_signature, "Xen", + strscpy((char *)&boot_params->efi_info.efi_loader_signature, "Xen", sizeof(boot_params->efi_info.efi_loader_signature)); boot_params->efi_info.efi_systab = (__u32)__pa(efi_systab_xen); boot_params->efi_info.efi_systab_hi = (__u32)(__pa(efi_systab_xen) >> 32);
`strncpy` is deprecated for use on NUL-terminated destination strings [1]. `efi_loader_signature` has space for 4 bytes. We are copying "Xen" (3 bytes) plus a NUL-byte which makes 4 total bytes. With that being said, there is currently not a bug with the current `strncpy()` implementation in terms of buffer overreads but we should favor a more robust string interface either way. A suitable replacement is `strscpy` [2] due to the fact that it guarantees NUL-termination on the destination buffer while being functionally the same in this case. 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://github.com/KSPP/linux/issues/90 Cc: linux-hardening@vger.kernel.org Cc: Kees Cook <keescook@chromium.org> Signed-off-by: Justin Stitt <justinstitt@google.com> --- Note: build-tested --- arch/x86/xen/efi.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c change-id: 20230911-strncpy-arch-x86-xen-efi-c-14292f5a79ee Best regards, -- Justin Stitt <justinstitt@google.com>