vhost: stick to -errno error return convention

[PATCH 05/10] vhost-backend: avoid overflow on memslots_limit

Posted by Roman Kagan 4 years, 3 months ago

Fix the (hypothetical) potential problem when the value parsed out of
the vhost module parameter in sysfs overflows the return value from
vhost_kernel_memslots_limit.

Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru>
---
 hw/virtio/vhost-backend.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
index b65f8f7e97..44f7dbb243 100644
--- a/hw/virtio/vhost-backend.c
+++ b/hw/virtio/vhost-backend.c
@@ -58,7 +58,7 @@ static int vhost_kernel_memslots_limit(struct vhost_dev *dev)
     if (g_file_get_contents("/sys/module/vhost/parameters/max_mem_regions",
                             &s, NULL, NULL)) {
         uint64_t val = g_ascii_strtoull(s, NULL, 10);
-        if (!((val == G_MAXUINT64 || !val) && errno)) {
+        if (val < INT_MAX && val > 0) {
             g_free(s);
             return val;
         }
-- 
2.33.1

Re: [PATCH 05/10] vhost-backend: avoid overflow on memslots_limit

Posted by Philippe Mathieu-Daudé 4 years, 3 months ago

On 11/11/21 16:33, Roman Kagan wrote:
> Fix the (hypothetical) potential problem when the value parsed out of
> the vhost module parameter in sysfs overflows the return value from
> vhost_kernel_memslots_limit.
> 
> Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru>
> ---
>  hw/virtio/vhost-backend.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
> index b65f8f7e97..44f7dbb243 100644
> --- a/hw/virtio/vhost-backend.c
> +++ b/hw/virtio/vhost-backend.c
> @@ -58,7 +58,7 @@ static int vhost_kernel_memslots_limit(struct vhost_dev *dev)
>      if (g_file_get_contents("/sys/module/vhost/parameters/max_mem_regions",
>                              &s, NULL, NULL)) {
>          uint64_t val = g_ascii_strtoull(s, NULL, 10);

Would using qemu_strtou64() simplify this?

> -        if (!((val == G_MAXUINT64 || !val) && errno)) {
> +        if (val < INT_MAX && val > 0) {
>              g_free(s);
>              return val;
>          }
>

Re: [PATCH 05/10] vhost-backend: avoid overflow on memslots_limit

Posted by Roman Kagan 4 years, 3 months ago

On Thu, Nov 11, 2021 at 06:59:43PM +0100, Philippe Mathieu-Daudé wrote:
> On 11/11/21 16:33, Roman Kagan wrote:
> > Fix the (hypothetical) potential problem when the value parsed out of
> > the vhost module parameter in sysfs overflows the return value from
> > vhost_kernel_memslots_limit.
> > 
> > Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru>
> > ---
> >  hw/virtio/vhost-backend.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
> > index b65f8f7e97..44f7dbb243 100644
> > --- a/hw/virtio/vhost-backend.c
> > +++ b/hw/virtio/vhost-backend.c
> > @@ -58,7 +58,7 @@ static int vhost_kernel_memslots_limit(struct vhost_dev *dev)
> >      if (g_file_get_contents("/sys/module/vhost/parameters/max_mem_regions",
> >                              &s, NULL, NULL)) {
> >          uint64_t val = g_ascii_strtoull(s, NULL, 10);
> 
> Would using qemu_strtou64() simplify this?

I'm afraid not.  None of the existing strtoXX converting functions has
the desired output range (0 < retval < INT_MAX), so the following
condition will remain necessary anyway; then it doesn't seem to matter
which particular parser is used to extract the value which is in the
range, so I left the one that was already there to reduce churn.

> 
> > -        if (!((val == G_MAXUINT64 || !val) && errno)) {
> > +        if (val < INT_MAX && val > 0) {
> >              g_free(s);
> >              return val;
> >          }

Thanks,
Roman.

Re: [PATCH 05/10] vhost-backend: avoid overflow on memslots_limit

Posted by Daniel P. Berrangé 4 years, 3 months ago

On Fri, Nov 12, 2021 at 10:46:46AM +0300, Roman Kagan wrote:
> On Thu, Nov 11, 2021 at 06:59:43PM +0100, Philippe Mathieu-Daudé wrote:
> > On 11/11/21 16:33, Roman Kagan wrote:
> > > Fix the (hypothetical) potential problem when the value parsed out of
> > > the vhost module parameter in sysfs overflows the return value from
> > > vhost_kernel_memslots_limit.
> > > 
> > > Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru>
> > > ---
> > >  hw/virtio/vhost-backend.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
> > > index b65f8f7e97..44f7dbb243 100644
> > > --- a/hw/virtio/vhost-backend.c
> > > +++ b/hw/virtio/vhost-backend.c
> > > @@ -58,7 +58,7 @@ static int vhost_kernel_memslots_limit(struct vhost_dev *dev)
> > >      if (g_file_get_contents("/sys/module/vhost/parameters/max_mem_regions",
> > >                              &s, NULL, NULL)) {
> > >          uint64_t val = g_ascii_strtoull(s, NULL, 10);
> > 
> > Would using qemu_strtou64() simplify this?
> 
> I'm afraid not.  None of the existing strtoXX converting functions has
> the desired output range (0 < retval < INT_MAX), so the following
> condition will remain necessary anyway; then it doesn't seem to matter
> which particular parser is used to extract the value which is in the
> range, so I left the one that was already there to reduce churn.

If  qemu_strtou64() can't handle all values in (0 < retval < INT_MAX)
isn't that a bug in qemu_strtou64 ?


Regards,
Daniel
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Re: [PATCH 05/10] vhost-backend: avoid overflow on memslots_limit

Posted by Roman Kagan 4 years, 3 months ago

On Fri, Nov 12, 2021 at 09:56:17AM +0000, Daniel P. Berrangé wrote:
> On Fri, Nov 12, 2021 at 10:46:46AM +0300, Roman Kagan wrote:
> > On Thu, Nov 11, 2021 at 06:59:43PM +0100, Philippe Mathieu-Daudé wrote:
> > > On 11/11/21 16:33, Roman Kagan wrote:
> > > > Fix the (hypothetical) potential problem when the value parsed out of
> > > > the vhost module parameter in sysfs overflows the return value from
> > > > vhost_kernel_memslots_limit.
> > > > 
> > > > Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru>
> > > > ---
> > > >  hw/virtio/vhost-backend.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
> > > > index b65f8f7e97..44f7dbb243 100644
> > > > --- a/hw/virtio/vhost-backend.c
> > > > +++ b/hw/virtio/vhost-backend.c
> > > > @@ -58,7 +58,7 @@ static int vhost_kernel_memslots_limit(struct vhost_dev *dev)
> > > >      if (g_file_get_contents("/sys/module/vhost/parameters/max_mem_regions",
> > > >                              &s, NULL, NULL)) {
> > > >          uint64_t val = g_ascii_strtoull(s, NULL, 10);
> > > 
> > > Would using qemu_strtou64() simplify this?
> > 
> > I'm afraid not.  None of the existing strtoXX converting functions has
> > the desired output range (0 < retval < INT_MAX), so the following
> > condition will remain necessary anyway; then it doesn't seem to matter
> > which particular parser is used to extract the value which is in the
> > range, so I left the one that was already there to reduce churn.
> 
> If  qemu_strtou64() can't handle all values in (0 < retval < INT_MAX)
> isn't that a bug in qemu_strtou64 ?

I must have been unclear.  It sure can handle all values in this range;
the point is that the range check after it would still be needed, so
switching from g_ascii_strtoull to qemu_strtoXX saves nothing, therefore
I left it as it was.

Thanks,
Roman.