Re: [PATCH v3] audit: Add generic compat syscall support
Catalin and audit maintainers,
On 01/23/2014 11:51 PM, Catalin Marinas wrote:
On Fri, Jan 17, 2014 at 08:03:15AM +0000, AKASHI Takahiro wrote:
> lib/audit.c provides a generic definition for auditing system calls.
> This patch extends it for compat syscall support on bi-architectures
> (32/64-bit) by adding lib/compat_audit.c when CONFIG_COMPAT enabled.
>
> Each architecture that wants to use this must define audit_is_compat()
> in asm/audit.h.
>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi(a)linaro.org>
I'm not familiar with the audit subsystem but I have some (cosmetic)
comments below.
> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index bf1ef22..3d71949 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -78,6 +78,15 @@ extern int is_audit_feature_set(int which);
> extern int __init audit_register_class(int class, unsigned *list);
> extern int audit_classify_syscall(int abi, unsigned syscall);
> extern int audit_classify_arch(int arch);
> +#if defined(CONFIG_AUDIT_GENERIC) && defined(CONFIG_COMPAT)
> +extern unsigned compat_write_class[];
> +extern unsigned compat_read_class[];
> +extern unsigned compat_dir_class[];
> +extern unsigned compat_chattr_class[];
> +extern unsigned compat_signal_class[];
> +
> +extern int audit_classify_compat_syscall(int abi, unsigned syscall);
> +#endif
>
> /* audit_names->type values */
> #define AUDIT_TYPE_UNKNOWN 0 /* we don't know yet */
> diff --git a/lib/Makefile b/lib/Makefile
> index a459c31..73ea908 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -93,6 +93,9 @@ obj-$(CONFIG_TEXTSEARCH_BM) += ts_bm.o
> obj-$(CONFIG_TEXTSEARCH_FSM) += ts_fsm.o
> obj-$(CONFIG_SMP) += percpu_counter.o
> obj-$(CONFIG_AUDIT_GENERIC) += audit.o
> +ifeq ($(CONFIG_COMPAT),y)
> +obj-$(CONFIG_AUDIT_GENERIC) += compat_audit.o
> +endif
You could use a CONFIG_AUDIT_COMPAT_GENERIC and simplify other #ifdefs
as well.
I will add the following in lib/Kconfig:
config AUDIT_COMPAT_GENERIC
depends on AUDIT_GENERIC & COMPAT
default y
> --- a/lib/audit.c
> +++ b/lib/audit.c
> @@ -1,6 +1,7 @@
> #include <linux/init.h>
> #include <linux/types.h>
> #include <linux/audit.h>
> +#include <asm/audit.h>
> #include <asm/unistd.h>
>
> static unsigned dir_class[] = {
> @@ -30,11 +31,20 @@ static unsigned signal_class[] = {
>
> int audit_classify_arch(int arch)
> {
> +#ifdef CONFIG_COMPAT
> + if (audit_is_compat(arch))
> + return 1;
> +#endif
> return 0;
> }
Here and in other places, just define a default audit_is_compat()
functions which returns false when !CONFIG_COMPAT to avoid the #ifdefs.
OK. With Richard's comment, the definition below will be added
to uapi/linux/audit.h:
#ifdef CONFIG_COMPAT
#define audit_is_compat(arch) (!!((arch) & __AUDIT_ARCH_64BIT))
#else
#define audit_is_compat(arch) false
#endif
> diff --git a/lib/compat_audit.c b/lib/compat_audit.c
> new file mode 100644
> index 0000000..94f6480
> --- /dev/null
> +++ b/lib/compat_audit.c
> @@ -0,0 +1,51 @@
> +#include <linux/init.h>
> +#include <linux/types.h>
> +/* FIXME: this might be architecture dependent */
> +#include <asm/unistd_32.h>
It most likely is architecture dependent.
I'm wondering what name is the most appropriate in this case.
Most archictures have __NR_xyz definitions in "unistd_32.h",
but arm64 doesn't have it, instead "unistd32." which contains
only __SYSCALL(xyz, NO). Confusing?
> +int audit_classify_compat_syscall(int abi, unsigned syscall)
> +{
> + switch (syscall) {
> +#ifdef __NR_open
> + case __NR_open:
> + return 2;
> +#endif
> +#ifdef __NR_openat
> + case __NR_openat:
> + return 3;
> +#endif
> +#ifdef __NR_socketcall
> + case __NR_socketcall:
> + return 4;
> +#endif
> + case __NR_execve:
> + return 5;
> + default:
> + return 1;
> + }
> +}
BTW, since they aren't many, you could get the arch code to define
__NR_compat_open etc. explicitly and use these. On arm64 we have a few
of these defined to avoid name collision in signal handling code.
Again, most architecture have their own unistd32.h for compat system calls,
and use __NR_open-like naming.
It's unlikely for these archs to migrate to "generic compat" auditing,
but I believe that '__NR_open'-like naming is better because we may be able to
avoid
arch-specific changes even for future(?) syscall-related enhancements in audit.
But, anyway, it's up to audit maintainer's preference.
Thanks,
-Takahiro AKASHI