linux-kernel - Re: [PATCH 1/2] ima: Free IMA measurement buffer on error

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Date:   Wed, 3 Feb 2021 09:47:53 -0800
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Cc:     zohar@...ux.ibm.com, dmitry.kasatkin@...il.com,
        ebiederm@...ssion.com, gregkh@...uxfoundation.org,
        sashal@...nel.org, tyhicks@...ux.microsoft.com,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 1/2] ima: Free IMA measurement buffer on error

On 1/22/21 2:30 PM, Thiago Jung Bauermann wrote:
> 
> Hi Lakshmi,
> 
> Lakshmi Ramasubramanian <nramas@...ux.microsoft.com> writes:
> 
>> IMA allocates kernel virtual memory to carry forward the measurement
>> list, from the current kernel to the next kernel on kexec system call,
>> in ima_add_kexec_buffer() function.  In error code paths this memory
>> is not freed resulting in memory leak.
>>
>> Free the memory allocated for the IMA measurement list in
>> the error code paths in ima_add_kexec_buffer() function.
>>
>> Signed-off-by: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
>> Suggested-by: Tyler Hicks <tyhicks@...ux.microsoft.com>
>> Fixes: 7b8589cc29e7 ("ima: on soft reboot, save the measurement list")
>> ---
>>   security/integrity/ima/ima_kexec.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
>> index 121de3e04af2..212145008a01 100644
>> --- a/security/integrity/ima/ima_kexec.c
>> +++ b/security/integrity/ima/ima_kexec.c
>> @@ -119,12 +119,14 @@ void ima_add_kexec_buffer(struct kimage *image)
>>   	ret = kexec_add_buffer(&kbuf);
>>   	if (ret) {
>>   		pr_err("Error passing over kexec measurement buffer.\n");
>> +		vfree(kexec_buffer);
>>   		return;
>>   	}
> 
> This is a good catch.

Thanks.

> 
>>   
>>   	ret = arch_ima_add_kexec_buffer(image, kbuf.mem, kexec_segment_size);
>>   	if (ret) {
>>   		pr_err("Error passing over kexec measurement buffer.\n");
>> +		vfree(kexec_buffer);
>>   		return;
>>   	}
> 
> But this would cause problems, because the buffer is still there in the
> kimage and would cause kimage_load_segment() to access invalid memory.
> 
> There's no function to undo a kexec_add_buffer() to avoid this problem,
> so I'd suggest just accepting the leak in this case. Fortunately, the
> current implementations of arch_ima_add_kexec_buffer() are very simple
> and cannot fail, so this is a theoretical problem.
> 

Agreed. I'll post a new patch with the above change removed.

thanks,
  -lakshmi