Re: [Qemu-devel] [PATCH v4] vl: exit if maxcpus is negative

[Philippe Mathieu-Daudé]

Hi Seeteena,

On 08/29/2017 02:45 AM, Seeteena Thoufeek wrote:
> ---Steps to Reproduce---
>
> When passed a negative number to 'maxcpus' parameter, Qemu aborts
> with a core dump.
>
> Run the following command with maxcpus argument as negative number
>
> ppc64-softmmu/qemu-system-ppc64 --nographic -vga none -machine
> pseries,accel=kvm,kvm-type=HV -m size=200g -device virtio-blk-pci,
> drive=rootdisk -drive file=/home/images/pegas-1.0-ppc64le.qcow2,
> if=none,cache=none,id=rootdisk,format=qcow2 -monitor telnet
> :127.0.0.1:1234,server,nowait -net nic,model=virtio -net
> user -redir tcp:2000::22 -device nec-usb-xhci -smp 8,cores=1,
> threads=1,maxcpus=-12
>
> (process:12149): GLib-ERROR **: gmem.c:130: failed to allocate
>   18446744073709550568 bytes
>
> Trace/breakpoint trap
>
> Reported-by: R.Nageswara Sastry <address@hidden>
> Signed-off-by: Seeteena Thoufeek <address@hidden>
> ---
> v1 -> v2:
>    - Fix the error check in vl.c to make it generic.
> v2 -> v3:
>    - Fix coding style pointed out by patchew.
>    - Fix check for "<= 0" instead of just "< 0".
> v3 -> v4:
>    - Fix subject line.
>    - Removed space before ":" from vl.c:1248
>    - Removed Reviewed-by: flag.
> ---
>   vl.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/vl.c b/vl.c
> index 8e247cc..2d9e73d 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -1244,7 +1244,10 @@ static void smp_parse(QemuOpts *opts)
>           }
>   
>           max_cpus = qemu_opt_get_number(opts, "maxcpus", cpus);
> -
> +        if (max_cpus <= 0) {
> +            error_report("Invalid max_cpus: %d", max_cpus);

I disagree with this patch, I think the correct fix is to declare 
max_cpus as unsigned.
Looking at the codebase I can't find any signed use of it.

> +            exit(1);
> +        }
>           if (max_cpus < cpus) {
>               error_report("maxcpus must be equal to or greater than smp");
>               exit(1);

Regards,

Phil.