Re: [RFC v2 4/7] modsig: add integrity_module_check hook

[Serge Hallyn <serge.hallyn@canonical.com>]

Quoting Dmitry Kasatkin (dmitry.kasatkin@intel.com):
> IMA measures/appraises modules when modprobe or insmod opens and read them.
> Unfortunately, there are no guarantees between what is read by userspace and
> what is passed to the kernel via load_module system call. This patch adds a
> hook called integrity_module_check() to verify the integrity of the module
> being loaded.
> 
> Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
> ---
>  include/linux/integrity.h |   10 ++++++++++
>  kernel/module.c           |    9 +++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/include/linux/integrity.h b/include/linux/integrity.h
> index 66c5fe9..a80ec06 100644
> --- a/include/linux/integrity.h
> +++ b/include/linux/integrity.h
> @@ -37,4 +37,14 @@ static inline void integrity_inode_free(struct inode *inode)
>  	return;
>  }
>  #endif /* CONFIG_INTEGRITY_H */
> +
> +#ifdef CONFIG_INTEGRITY_MODULES
> +int integrity_module_check(const void *hdr, const unsigned long len);

sadly not bisect-safe, since integrity_module_check() is defined in
the next patch.

> +#else
> +static inline int integrity_module_check(const void *buf, unsigned long len)
> +{
> +	return 0;
> +}
> +#endif
> +
>  #endif /* _LINUX_INTEGRITY_H */
> diff --git a/kernel/module.c b/kernel/module.c
> index 4edbd9c..791da47 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -58,6 +58,7 @@
>  #include <linux/jump_label.h>
>  #include <linux/pfn.h>
>  #include <linux/bsearch.h>
> +#include <linux/integrity.h>
>  
>  #define CREATE_TRACE_POINTS
>  #include <trace/events/module.h>
> @@ -2437,6 +2438,14 @@ static int copy_and_check(struct load_info *info,
>  
>  	info->hdr = hdr;
>  	info->len = len;
> +
> +	err = integrity_module_check(hdr, len);
> +	if (err < 0)
> +		goto free_hdr;
> +
> +	/* cut signature tail */
> +	info->len = err;
> +
>  	return 0;
>  
>  free_hdr:
> -- 
> 1.7.9.5
> 
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