On Tue, Nov 18, 2014 at 3:12 PM, Mathias Krause <minipli@xxxxxxxxxxxxxx> wrote: > On 18 November 2014 01:45, Kees Cook <keescook@xxxxxxxxxxxx> wrote: >> On Mon, Nov 17, 2014 at 3:20 PM, Mathias Krause <minipli@xxxxxxxxxxxxxx> wrote: >>> On 17 November 2014 21:02, Kees Cook <keescook@xxxxxxxxxxxx> wrote: >>>> This prefixes all crypto module loading with "crypto-" so we never run >>>> the risk of exposing module auto-loading to userspace via a crypto API, >>>> as demonstrated by Mathias Krause: >>>> >>>> https://lkml.org/lkml/2013/3/4/70 >>>> >>>> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> >>>> --- >>>> v2: >>>> - added missing #include, thanks to minipli >>>> - built with allmodconfig >>>> [...snip...] >>>> diff --git a/include/linux/crypto.h b/include/linux/crypto.h >>>> index d45e949699ea..d14230f6e977 100644 >>>> --- a/include/linux/crypto.h >>>> +++ b/include/linux/crypto.h >>>> @@ -26,6 +26,13 @@ >>>> #include <linux/uaccess.h> >>>> >>>> /* >>>> + * Autoloaded crypto modules should only use a prefixed name to avoid allowing >>>> + * arbitrary modules to be loaded. >>>> + */ >>>> +#define MODULE_ALIAS_CRYPTO(name) \ >>>> + MODULE_ALIAS("crypto-" name) >>> >>> This would break userland relying on the old aliases, e.g. 'modprobe >>> aes' no longer works. >>> >>> Why not have both aliases, one with the "crypto-" prefix for on-demand >>> loading within the crypto API and one without for manual loading from >>> userland? E.g., something like this: >>> >>> #define MODULE_ALIAS_CRYPTO(name) \ >>> MODULE_ALIAS(name); \ >>> MODULE_ALIAS("crypto-" name) >>> >>> That would prevent the userland breakage and still achieves the goal >>> of restricting the request_module() call offered by the means of the >>> AF_ALG API. >> >> That was my intention originally, and I should go back to it. The >> trouble is with the use of __UNIQUE_ID in the MODULE_ALIAS macro. It >> uses __LINE__ to produce the id, so the suggested macro expansion >> (which is what I started with) won't work on non-gcc compilers. >> >> I haven't found any solutions for C89 version of gcc's __COUNTER__, >> and I haven't found any C89 ways to force a macro to be expanded as >> being multi-line. > > Well, clang should support it as well, according to [1]. But still, a > compiler independent solution would be nice. > Anyway, the __COUNTER__ support is gcc >= 4.3 only. So, according to > Documentation/Changes, stating gcc 3.2 is the minimum supported > version for compiling the kernel, this would be a no-go, too. > > [1] http://clang.llvm.org/docs/LanguageExtensions.html#builtin-macros Yeah, it's the avr32 auto builder that throws the warnings, so I assume it's using a pre-4.3 gcc. >> I'd like to avoid having to open-code both MODULE_ALIAS and >> MODULE_ALIAS_CRYPTO in each module's source. >> >> Anyone see some sneaky way to accomplish this? > > Unfortunately, I do not ... beside this, maybe: > > #define MODULE_ALIAS_CRYPTO(name) \ > __MODULE_INFO(alias, alias_userland, name); \ > __MODULE_INFO(alias, alias_crypto, "crypto-" name) > > Looks ugly, but works. ;) AAh! Yes, that's perfect! I will spin it this way. Thank you thank you! -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
