Re: [PATCH v3 3/4] add kexec_cmdline used to ima

[Mimi Zohar <zohar@linux.ibm.com>]

On Mon, 2019-04-29 at 14:47 -0700, Prakhar Srivastava wrote:
> From: Prakhar Srivastava <prsriva02@gmail.com>
> 
> prepend the kernel file name to kexec_cmdline 
> before measuring the buffer.
> 

kexec doesn't really know or care about IMA.  Other than the IMA call,
itself, nothing should be added to kexec files.  As mentioned in 1/4,
the IMA hook would be named something like ima_kexec_cmdline().

Mimi

> Signed-off-by: Prakhar Srivastava <prsriva02@gmail.com>
> ---
>  kernel/kexec_core.c | 57 +++++++++++++++++++++++++++++++++++++++++++++
>  kernel/kexec_file.c | 14 +++++++++++
>  2 files changed, 71 insertions(+)
> 
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index d7140447be75..4667f03d406e 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -1213,3 +1213,60 @@ void __weak arch_kexec_protect_crashkres(void)
>  
>  void __weak arch_kexec_unprotect_crashkres(void)
>  {}
> +
> +/**
> + * kexec_cmdline_prepend_img_name - prepare the buffer with cmdline
> + * that needs to be measured
> + * @outbuf - out buffer that contains the formated string
> + * @kernel_fd - the file identifier for the kerenel image
> + * @cmdline_ptr - ptr to the cmdline buffer
> + * @cmdline_len - len of the buffer.
> + *
> + * This generates a buffer in the format Kerenelfilename::cmdline
> + *
> + * On success return 0.
> + * On failure return -EINVAL.
> + */
> +int kexec_cmdline_prepend_img_name(char **outbuf, int kernel_fd,
> +				const char *cmdline_ptr,
> +				unsigned long cmdline_len)
> +{
> +	int ret = -EINVAL;
> +	struct fd f = {};
> +	int size = 0;
> +	char *buf = NULL;
> +	char delimiter[] = "::";
> +
> +	if (!outbuf || !cmdline_ptr)
> +		goto out;
> +
> +	f = fdget(kernel_fd);
> +	if (!f.file)
> +		goto out;
> +
> +	size = (f.file->f_path.dentry->d_name.len + cmdline_len - 1+
> +			ARRAY_SIZE(delimiter)) - 1;
> +
> +	buf = kzalloc(size, GFP_KERNEL);
> +	if (!buf)
> +		goto out;
> +
> +	memcpy(buf, f.file->f_path.dentry->d_name.name,
> +		f.file->f_path.dentry->d_name.len);
> +	memcpy(buf + f.file->f_path.dentry->d_name.len,
> +		delimiter, ARRAY_SIZE(delimiter) - 1);
> +	memcpy(buf + f.file->f_path.dentry->d_name.len +
> +		ARRAY_SIZE(delimiter) - 1,
> +		cmdline_ptr, cmdline_len - 1);
> +
> +	*outbuf = buf;
> +	ret = size;
> +
> +	pr_debug("kexec cmdline buff: %s\n", buf);
> +
> +out:
> +	if (f.file)
> +		fdput(f);
> +
> +	return ret;
> +}
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index f1d0e00a3971..d287e139085c 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -191,6 +191,8 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
>  	int ret = 0;
>  	void *ldata;
>  	loff_t size;
> +	char *buff_to_measure = NULL;
> +	int buff_to_measure_size = 0;
>  
>  	ret = kernel_read_file_from_fd(kernel_fd, &image->kernel_buf,
>  				       &size, INT_MAX, READING_KEXEC_IMAGE);
> @@ -241,6 +243,16 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
>  			ret = -EINVAL;
>  			goto out;
>  		}
> +
> +		/* IMA measures the cmdline args passed to the next kernel*/
> +		buff_to_measure_size =
> +			kexec_cmdline_prepend_img_name(&buff_to_measure,
> +			kernel_fd, image->cmdline_buf, image->cmdline_buf_len);
> +
> +		ima_buffer_check(buff_to_measure, buff_to_measure_size,
> +					"kexec_cmdline");
> +
> +
>  	}
>  
>  	/* Call arch image load handlers */
> @@ -253,7 +265,9 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
>  
>  	image->image_loader_data = ldata;
>  out:
> +
>  	/* In case of error, free up all allocated memory in this function */
> +	kfree(buff_to_measure);
>  	if (ret)
>  		kimage_file_post_load_cleanup(image);
>  	return ret;