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Re: [Xen-devel] [PATCH v5 12/17] xen/libxc: sched: DOMCTL_*vcpuaffinity works with hard and soft affinity

On 12/03/2013 10:06 AM, Jan Beulich wrote:
On 03.12.13 at 11:02, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
On 02.12.13 at 19:29, Dario Faggioli <dario.faggioli@xxxxxxxxxx> wrote:
+                goto setvcpuaffinity_out;
+            /*
+             * We both set a new affinity and report back to the caller what
+             * the scheduler will be effectively using.
+             */
+            if ( vcpuaff->flags & XEN_VCPUAFFINITY_HARD )
+            {
+                ret = xenctl_bitmap_to_bitmap(cpumask_bits(new_affinity),
+                                              &vcpuaff->cpumap_hard,
+                                              vcpuaff->cpumap_hard.nr_bits);

There's no code above range checking vcpuaff->cpumap_hard.nr_bits,
yet xenctl_bitmap_to_bitmap() uses the passed in value to write into
the array pointed to by the first argument. Why is this not
xenctl_bitmap_to_cpumask() in the first place?

And just to make it explicit - with fundamental flaws like this, I'm
not certain anymore whether we really ought to rush this series
in for 4.4.

I'm certainly getting nervous about the prospect. However, the above bug would only be triggered by bad input from domain 0, right? I suppose even that would be a potential security issue in a highly disaggregated environment.

Other bugs in this patch would be similar. This path is taken on domain creation IIUC; so bugs in this particular patch would probably either be unexpected behavior of the affinities, or failure to handle unusual input from a trusted source (domain 0).


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