Re: [RHEL7 qemu-kvm PATCH 2/3] s390x: Fix vm name copy length

[Miroslav Rezanina <mrezanin@redhat.com>]

----- Original Message -----
> From: "Thomas Huth" <thuth@redhat.com>
> To: "Miroslav Rezanina" <mrezanin@redhat.com>
> Cc: "qemu-s390x" <qemu-s390x@nongnu.org>, "Philippe Mathieu-Daudé" <philmd@redhat.com>, qemu-devel@nongnu.org
> Sent: Monday, January 11, 2021 1:54:06 PM
> Subject: Re: [RHEL7 qemu-kvm PATCH 2/3] s390x: Fix vm name copy length
> 
> On 11/01/2021 13.42, Miroslav Rezanina wrote:
> > 
> > 
> > ----- Original Message -----
> >> From: "Thomas Huth" <thuth@redhat.com>
> >> To: "Philippe Mathieu-Daudé" <philmd@redhat.com>, mrezanin@redhat.com,
> >> qemu-devel@nongnu.org, "qemu-s390x"
> >> <qemu-s390x@nongnu.org>
> >> Sent: Monday, January 11, 2021 1:24:57 PM
> >> Subject: Re: [RHEL7 qemu-kvm PATCH 2/3] s390x: Fix vm name copy length
> >>
> >> On 11/01/2021 13.10, Philippe Mathieu-Daudé wrote:
> >>> Hi Miroslav,
> >>>
> >>> On 1/11/21 12:30 PM, mrezanin@redhat.com wrote:
> >>>> From: Miroslav Rezanina <mrezanin@redhat.com>
> >>>>
> >>>> There are two cases when vm name is copied but closing \0 can be lost
> >>>> in case name is too long (>=256 characters).
> >>>>
> >>>> Updating length to copy so there is space for closing \0.
> >>>>
> >>>> Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
> >>>> ---
> >>>>    target/s390x/kvm.c         | 2 +-
> >>>>    target/s390x/misc_helper.c | 4 +++-
> >>>>    2 files changed, 4 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> >>>> index b8385e6b95..2313b5727e 100644
> >>>> --- a/target/s390x/kvm.c
> >>>> +++ b/target/s390x/kvm.c
> >>>> @@ -1918,7 +1918,7 @@ static void insert_stsi_3_2_2(S390CPU *cpu, __u64
> >>>> addr, uint8_t ar)
> >>>>         */
> >>>>        if (qemu_name) {
> >>>>            strncpy((char *)sysib.ext_names[0], qemu_name,
> >>>> -                sizeof(sysib.ext_names[0]));
> >>>> +                sizeof(sysib.ext_names[0]) - 1);
> >>>>        } else {
> >>>>            strcpy((char *)sysib.ext_names[0], "KVMguest");
> >>>>        }
> >>>
> >>> What about using strpadcpy() instead?
> >>
> >> Yes, strpadcpy is the better way here - this field has to be padded with
> >> zeroes, so doing "- 1" is wrong here.
> > 
> > Hi Thomas,
> > 
> > as I wrote in reply to Phillipe - the array is memset to zeroes before the
> > if so we
> > are sure it's padded with zeroes (in this occurrence, not true for second
> > one).
> 
> Ok, but dropping the last character is still wrong here. The ext_names do
> not need to be terminated with a \0 if they have the full length.

Oh, they do not have to end with \0??? I did not know it. In that case we
probably have to use strpadcpy to get rid of the compiler warning.

Mirek
> 
>   Thomas
> 

-- 
Miroslav Rezanina
Software Engineer - Virtualization Team Maintainer