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From:   Thiago Jung Bauermann <bauerman@linux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Cc:     zohar@linux.ibm.com, dmitry.kasatkin@gmail.com,
        ebiederm@xmission.com, gregkh@linuxfoundation.org,
        sashal@kernel.org, tyhicks@linux.microsoft.com,
        linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 1/2] ima: Free IMA measurement buffer on error
In-reply-to: <20210121173003.18324-1-nramas@linux.microsoft.com>
Date:   Fri, 22 Jan 2021 19:30:20 -0300
Message-ID: <87eeic1u6b.fsf@manicouagan.localdomain>
MIME-Version: 1.0
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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.

-- 
Thiago Jung Bauermann
IBM Linux Technology Center