linux-kernel - Re: [PATCH 07/13] kexec: Implementation of new syscall kexec_file

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Date:	Fri, 6 Jun 2014 14:56:05 +0800
From:	WANG Chao <chaowang@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	ebiederm@...ssion.com, hpa@...or.com, mjg59@...f.ucam.org,
	greg@...ah.com, bp@...en8.de, jkosina@...e.cz, dyoung@...hat.com,
	bhe@...hat.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 07/13] kexec: Implementation of new syscall
 kexec_file_load

On 06/03/14 at 09:06am, Vivek Goyal wrote:
> Previous patch provided the interface definition and this patch prvides
> implementation of new syscall.
> 
> Previously segment list was prepared in user space. Now user space just
> passes kernel fd, initrd fd and command line and kernel will create a
> segment list internally.
> 
> This patch contains generic part of the code. Actual segment preparation
> and loading is done by arch and image specific loader. Which comes in
> next patch.
> 
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>

[..]
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index a3044e6..1ad4d60 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c

> +static int kimage_file_prepare_segments(struct kimage *image, int kernel_fd,
> +		int initrd_fd, const char __user *cmdline_ptr,
> +		unsigned long cmdline_len)
> +{
> +	int ret = 0;
> +	void *ldata;
> +
> +	ret = copy_file_from_fd(kernel_fd, &image->kernel_buf,
> +					&image->kernel_buf_len);
> +	if (ret)
> +		return ret;
> +
> +	/* Call arch image probe handlers */
> +	ret = arch_kexec_kernel_image_probe(image, image->kernel_buf,
> +						image->kernel_buf_len);
> +
> +	if (ret)
> +		goto out;
> +
> +	ret = copy_file_from_fd(initrd_fd, &image->initrd_buf,
> +					&image->initrd_buf_len);
> +	if (ret)
> +		goto out;
> +
> +	image->cmdline_buf = vzalloc(cmdline_len);

You should validate the upper/lower boundary of cmdline_len before
calling vzalloc. When cmdline_len is 0 or too large, vmalloc failure
message would be fired.

> +	if (!image->cmdline_buf)
> +		goto out;
> +
> +	ret = copy_from_user(image->cmdline_buf, cmdline_ptr, cmdline_len);
> +	if (ret) {
> +		ret = -EFAULT;
> +		goto out;
> +	}
> +
> +	image->cmdline_buf_len = cmdline_len;
> +
> +	/* command line should be a string with last byte null */
> +	if (image->cmdline_buf[cmdline_len - 1] != '\0') {
> +		ret = -EINVAL;
> +		goto out;
> +	}

Given the fact that command line is optional as well as initrd, I think
above chunk of code needs to update a bit for the case cmdline_len is 0
or cmdline_buf is pointing NULL?

Thanks
WANG Chao
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