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

[Lakshmi Ramasubramanian]

On 1/22/21 2:30 PM, Thiago Jung Bauermann wrote:
> Hi Lakshmi,
>
> Lakshmi Ramasubramanian <nramas@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx>
> > Suggested-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx>
> > 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