Re: [Qemu-devel] [for-2.11 PATCH 03/26] spapr_iommu: use g_strdup_printf() instead of snprintf()

[Greg Kurz <groug@kaod.org>]

[-- Attachment #1: Type: text/plain, Size: 2877 bytes --]

On Wed, 26 Jul 2017 13:37:03 +1000
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> On 26/07/17 03:58, Greg Kurz wrote:
> > Passing a stack allocated buffer of arbitrary length to snprintf()
> > without checking the return value can cause the resultant strings
> > to be silently truncated.  
> 
> The strings it is touching cannot be silently truncated as
> "tce-iommu-XXXXXXXX" are shorter than 32 chars.
> 

True but if the string was to be changed (unlikely, I admit) then we should
ensure the array is large enough. And anyway, this means we waste stack space,
which is suboptimal. As noted by David, it is a common practice in QEMU to use
g_strdup_printf().

> 
> > 
> > Signed-off-by: Greg Kurz <groug@kaod.org>
> > ---
> >  hw/ppc/spapr_iommu.c |   13 ++++++++-----
> >  1 file changed, 8 insertions(+), 5 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr_iommu.c b/hw/ppc/spapr_iommu.c
> > index e614621a8317..740d42608b61 100644
> > --- a/hw/ppc/spapr_iommu.c
> > +++ b/hw/ppc/spapr_iommu.c
> > @@ -252,17 +252,19 @@ static int spapr_tce_table_realize(DeviceState *dev)
> >  {
> >      sPAPRTCETable *tcet = SPAPR_TCE_TABLE(dev);
> >      Object *tcetobj = OBJECT(tcet);
> > -    char tmp[32];
> > +    gchar *tmp;
> >  
> >      tcet->fd = -1;
> >      tcet->need_vfio = false;
> > -    snprintf(tmp, sizeof(tmp), "tce-root-%x", tcet->liobn);
> > +    tmp = g_strdup_printf("tce-root-%x", tcet->liobn);
> >      memory_region_init(&tcet->root, tcetobj, tmp, UINT64_MAX);
> > +    g_free(tmp);
> >  
> > -    snprintf(tmp, sizeof(tmp), "tce-iommu-%x", tcet->liobn);
> > +    tmp = g_strdup_printf("tce-iommu-%x", tcet->liobn);
> >      memory_region_init_iommu(&tcet->iommu, sizeof(tcet->iommu),
> >                               TYPE_SPAPR_IOMMU_MEMORY_REGION,
> >                               tcetobj, tmp, 0);
> > +    g_free(tmp);
> >  
> >      QLIST_INSERT_HEAD(&spapr_tce_tables, tcet, list);
> >  
> > @@ -307,7 +309,7 @@ void spapr_tce_set_need_vfio(sPAPRTCETable *tcet, bool need_vfio)
> >  sPAPRTCETable *spapr_tce_new_table(DeviceState *owner, uint32_t liobn)
> >  {
> >      sPAPRTCETable *tcet;
> > -    char tmp[32];
> > +    gchar *tmp;
> >  
> >      if (spapr_tce_find_by_liobn(liobn)) {
> >          error_report("Attempted to create TCE table with duplicate"
> > @@ -318,8 +320,9 @@ sPAPRTCETable *spapr_tce_new_table(DeviceState *owner, uint32_t liobn)
> >      tcet = SPAPR_TCE_TABLE(object_new(TYPE_SPAPR_TCE_TABLE));
> >      tcet->liobn = liobn;
> >  
> > -    snprintf(tmp, sizeof(tmp), "tce-table-%x", liobn);
> > +    tmp = g_strdup_printf("tce-table-%x", liobn);
> >      object_property_add_child(OBJECT(owner), tmp, OBJECT(tcet), NULL);
> > +    g_free(tmp);
> >  
> >      object_property_set_bool(OBJECT(tcet), true, "realized", NULL);
> >  
> > 
> >   
> 
> 


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 181 bytes --]