Re: [Xen-devel] [PATCH] tools: Fix wild memory allocations from c/s 250f0b4 and 85d78b4

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 18/05/15 15:00, Boris Ostrovsky wrote:
> On 05/18/2015 08:57 AM, Andrew Cooper wrote:
>> These changesets cause the respective libxc functions to unconditonally
>> dereference their max_cpus/nodes parameters as part of initial memory
>> allocations.  It will fail at obtaining the correct number of
>> cpus/nodes from
>> Xen, as the guest handles will not be NULL.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
>> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
>> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
>> CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
>>
>> ---
>> Spotted by XenServers Coverity run.
>> ---
>>   tools/libxl/libxl.c               |    4 ++--
>>   tools/misc/xenpm.c                |    4 ++--
>>   tools/python/xen/lowlevel/xc/xc.c |    4 ++--
>>   3 files changed, 6 insertions(+), 6 deletions(-)
>
> xenpm bug is already fixed (commit
> b315cd9cce5b6da7ca89b2d7bad3fb01e7716044 n the staging tree).
>
> I am not sure I understand why Coverity complains about other spots.
> For example, in libxl_get_cpu_topology() num_cpus can be left
> uninitialized only if xc_cputopoinfo(ctx->xch, &num_cpus, NULL) fails,
> in which case we go to 'GC_FREE;  return ret;', so it's not ever used.

xc_cputopoinfo(ctx->xch, &num_cpus, NULL) unconditionally dereferences
and reads &num_cpus, and performs a memory allocation based on the result.

~Andrew

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