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: "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).

Mirek

> 
>   Thomas
> 

-- 
Miroslav Rezanina
Software Engineer - Virtualization Team Maintainer