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[1/2] ima: Free IMA measurement buffer on error

Message ID 20210121173003.18324-1-nramas@linux.microsoft.com
State Not Applicable
Headers show
Series [1/2] ima: Free IMA measurement buffer on error | expand

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Context Check Description
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snowpatch_ozlabs/checkpatch success total: 0 errors, 0 warnings, 0 checks, 14 lines checked
snowpatch_ozlabs/apply_patch success Successfully applied on branch powerpc/merge (41d8cb7ece7c81e4eb897ed7ec7d3c3d72fd0af4)

Commit Message

Lakshmi Ramasubramanian Jan. 21, 2021, 5:30 p.m. UTC
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@linux.microsoft.com>
Suggested-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Fixes: 7b8589cc29e7 ("ima: on soft reboot, save the measurement list")
---
 security/integrity/ima/ima_kexec.c | 2 ++
 1 file changed, 2 insertions(+)

Comments

Tyler Hicks Jan. 21, 2021, 5:35 p.m. UTC | #1
On 2021-01-21 09:30:02, Lakshmi Ramasubramanian wrote:
> 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@linux.microsoft.com>
> Suggested-by: Tyler Hicks <tyhicks@linux.microsoft.com>
> Fixes: 7b8589cc29e7 ("ima: on soft reboot, save the measurement list")

Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com>

Tyler

> ---
>  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;
>  	}
>  
>  	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;
>  	}
>  
> -- 
> 2.30.0
>
Thiago Jung Bauermann Jan. 22, 2021, 10:30 p.m. UTC | #2
Hi Lakshmi,

Lakshmi Ramasubramanian <nramas@linux.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@linux.microsoft.com>
> Suggested-by: Tyler Hicks <tyhicks@linux.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.

>  
>  	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.
Lakshmi Ramasubramanian Feb. 3, 2021, 5:47 p.m. UTC | #3
On 1/22/21 2:30 PM, Thiago Jung Bauermann wrote:
> 
> Hi Lakshmi,
> 
> Lakshmi Ramasubramanian <nramas@linux.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@linux.microsoft.com>
>> Suggested-by: Tyler Hicks <tyhicks@linux.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
diff mbox series

Patch

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;
 	}
 
 	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;
 	}