Re: [PATCH] kexec: avoid out of bounds in crash_exclude_mem_range()

[fuqiang wang]

On 2023/11/30 15:44, Baoquan He wrote:
> On 11/27/23 at 10:56am, fuqiang wang wrote:
> > When the split happened, judge whether mem->nr_ranges is equal to
> > mem->max_nr_ranges. If it is true, return -ENOMEM.
> >
> > The advantage of doing this is that it can avoid array bounds caused by
> > some bugs. E.g., Before commit 4831be702b95 ("arm64/kexec: Fix missing
> > extra range for crashkres_low."), reserve both high and low memories for
> > the crashkernel may cause out of bounds.
> >
> > On the other hand, move this code before the split to ensure that the
> > array will not be changed when return error.
> If out of array boundary is caused, means the laoding failed, whether
> the out of boundary happened or not. I don't see how this code change
> makes sense. Do I miss anything?
>
> Thanks
> Baoquan
Hi baoquan,

In some configurations, out of bounds may not cause crash_exclude_mem_range()
returns error, then the load will succeed.

E.g.
There is a cmem before execute crash_exclude_mem_range():

  cmem = {
    max_nr_ranges = 3
    nr_ranges = 2
    ranges = {
       {start = 1,      end = 1000}
       {start = 1001,    end = 2000}
    }
  }

After executing twice crash_exclude_mem_range() with the start/end params
100/200, 300/400 respectively, the cmem will be:

  cmem = {
    max_nr_ranges = 3
    nr_ranges = 4                    <== nr_ranges > max_nr_ranges
    ranges = {
      {start = 1,       end = 99  }
      {start = 201,     end = 299 }
      {start = 401,     end = 1000}
      {start = 1001,    end = 2000}  <== OUT OF BOUNDS
    }
  }

When an out of bounds occurs during the second execution, the function will not
return error.

Additionally, when the function returns error, means the load failed. It seems
meaningless to keep the original data unchanged. But in my opinion, this will
make this function more rigorous and more versatile. (However, I am not sure if
it is self-defeating and I hope to receive more suggestions).

Thanks
fuqiang


> > Signed-off-by: fuqiang wang <fuqiang.wang@xxxxxxxxxxxx>
> > ---
> >   kernel/crash_core.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> > index efe87d501c8c..ffdc246cf425 100644
> > --- a/kernel/crash_core.c
> > +++ b/kernel/crash_core.c
> > @@ -611,6 +611,9 @@ int crash_exclude_mem_range(struct crash_mem *mem,
> >   		}
> >   
> >   		if (p_start > start && p_end < end) {
> > +			/* Split happened */
> > +			if (mem->nr_ranges == mem->max_nr_ranges)
> > +				return -ENOMEM;
> >   			/* Split original range */
> >   			mem->ranges[i].end = p_start - 1;
> >   			temp_range.start = p_end + 1;
> > @@ -626,9 +629,6 @@ int crash_exclude_mem_range(struct crash_mem *mem,
> >   	if (!temp_range.end)
> >   		return 0;
> >   
> > -	/* Split happened */
> > -	if (i == mem->max_nr_ranges - 1)
> > -		return -ENOMEM;
> >   
> >   	/* Location where new range should go */
> >   	j = i + 1;
> > --
> > 2.42.0
> >
> >
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