Re: [PATCH 1/1] clk: tegra: tegra124-emc: Fix possible memory leak

[Leizhen (ThunderTown)]

On 2021/6/26 7:31, Stephen Boyd wrote:
> Quoting Zhen Lei (2021-06-17 01:27:59)
>> When krealloc() fails to expand the memory and returns NULL, the original
>> memory is not released. In this case, the original "timings" scale should
>> be maintained.
>>
>> Fixes: 888ca40e2843 ("clk: tegra: emc: Support multiple RAM codes")
>> Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
>> ---
> 
> Looks correct, but when does krealloc() return NULL? My read of the
> kerneldoc is that it would return the original memory if the new
> allocation "failed".

That must be the wrong description in the document. For example, the original
100-byte memory needs to be expanded to 200 bytes. If the memory allocation fails,
a non-null pointer is returned. People must think they've applied for it and
continue to use it, the end result is memory crashed.

I don't think the kernel needs to be different from libc's realloc().

The implementation of __do_krealloc() illustrates this as well:
        /* If the object still fits, repoison it precisely. */
        if (ks >= new_size) {
                p = kasan_krealloc((void *)p, new_size, flags);
                return (void *)p;
        }

        ret = kmalloc_track_caller(new_size, flags);			//enlarge, allocate new memory
	if (ret && p) {
                memcpy(ret, kasan_reset_tag(p), ks);			//copy the old content from 'p' to new memory 'ret'
        }

	return ret;							//ret may be NULL, if kmalloc_track_caller() failed



> 
> Reviewed-by: Stephen Boyd <sboyd@xxxxxxxxxx>
> 
> .
>