Re: [PATCH 07/13] kexec: Implementation of new syscall kexec_file_load

[Dave Young]

On 06/06/14 at 02:19pm, Vivek Goyal wrote:
> On Fri, Jun 06, 2014 at 02:56:05PM +0800, WANG Chao wrote:
> > 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@xxxxxxxxxx>
> > 
> > [..]
> > > 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.
> 
> What's the upper length of vzalloc(). I think if it is too big to alloc,
> then vzalloc() should return me an error?

function __vmalloc_node_range:
        if (!size || (size >> PAGE_SHIFT) > totalram_pages)
                goto fail;

So I think only checking cmdline_len == 0 is enough.

For the upper length shouldn't it be stripped to COMMAND_LINE_SIZE?


> > > +	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?
> 
> I agree. I think all this vzalloc(), copy_from_user() etc should be called
> only fir cmdline_len is non-zero. Will fix it.
> 
> Thanks
> Vivek
> 
> 
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