[Xen-devel] [PATCH for-4.13] xen/xsm: flask: Prevent NULL deference in flask_assign_{, dt}device()

[Xen-devel] [PATCH for-4.13] xen/xsm: flask: Prevent NULL deference in flask_assign_{, dt}device()

[Julien Grall]

flask_assign_{, dt}device() may be used to check whether you can test if
a device is assigned. In this case, the domain will be NULL.

However, flask_iommu_resource_use_perm() will be called and may end up
to deference a NULL pointer. This can be prevented by moving the call
after we check the validity for the domain pointer.

Coverity-ID: 1486741
Fixes: 71e617a6b8 ('use is_iommu_enabled() where appropriate...')
Signed-off-by: Julien Grall <julien.grall@arm.com>
---
 xen/xsm/flask/hooks.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
index 3b30827764..cf7f25cda2 100644
--- a/xen/xsm/flask/hooks.c
+++ b/xen/xsm/flask/hooks.c
@@ -1296,11 +1296,13 @@ static int flask_assign_device(struct domain *d, uint32_t machine_bdf)
     u32 dsid, rsid;
     int rc = -EPERM;
     struct avc_audit_data ad;
-    u32 dperm = flask_iommu_resource_use_perm(d);
+    u32 dperm;
 
     if ( !d )
         return flask_test_assign_device(machine_bdf);
 
+    dperm = flask_iommu_resource_use_perm(d);
+
     rc = current_has_perm(d, SECCLASS_RESOURCE, RESOURCE__ADD);
     if ( rc )
         return rc;
@@ -1355,11 +1357,13 @@ static int flask_assign_dtdevice(struct domain *d, const char *dtpath)
     u32 dsid, rsid;
     int rc = -EPERM;
     struct avc_audit_data ad;
-    u32 dperm = flask_iommu_resource_use_perm(d);
+    u32 dperm;
 
     if ( !d )
         return flask_test_assign_dtdevice(dtpath);
 
+    dperm = flask_iommu_resource_use_perm(d);
+
     rc = current_has_perm(d, SECCLASS_RESOURCE, RESOURCE__ADD);
     if ( rc )
         return rc;
-- 
2.11.0


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Re: [Xen-devel] [PATCH for-4.13] xen/xsm: flask: Prevent NULL deference in flask_assign_{, dt}device()

[Daniel De Graaf]

On 10/4/19 12:42 PM, Julien Grall wrote:
> flask_assign_{, dt}device() may be used to check whether you can test if
> a device is assigned. In this case, the domain will be NULL.
> 
> However, flask_iommu_resource_use_perm() will be called and may end up
> to deference a NULL pointer. This can be prevented by moving the call
> after we check the validity for the domain pointer.
> 
> Coverity-ID: 1486741
> Fixes: 71e617a6b8 ('use is_iommu_enabled() where appropriate...')
> Signed-off-by: Julien Grall <julien.grall@arm.com>

Acked-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>

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Re: [Xen-devel] [PATCH for-4.13] xen/xsm: flask: Prevent NULL deference in flask_assign_{, dt}device()

[Paul Durrant]

On Fri, 4 Oct 2019 at 17:42, Julien Grall <julien.grall@arm.com> wrote:
>
> flask_assign_{, dt}device() may be used to check whether you can test if
> a device is assigned. In this case, the domain will be NULL.
>
> However, flask_iommu_resource_use_perm() will be called and may end up
> to deference a NULL pointer. This can be prevented by moving the call
> after we check the validity for the domain pointer.
>
> Coverity-ID: 1486741
> Fixes: 71e617a6b8 ('use is_iommu_enabled() where appropriate...')
> Signed-off-by: Julien Grall <julien.grall@arm.com>

Reviewed-by: Paul Durrant <paul@xen.org>

> ---
>  xen/xsm/flask/hooks.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
> index 3b30827764..cf7f25cda2 100644
> --- a/xen/xsm/flask/hooks.c
> +++ b/xen/xsm/flask/hooks.c
> @@ -1296,11 +1296,13 @@ static int flask_assign_device(struct domain *d, uint32_t machine_bdf)
>      u32 dsid, rsid;
>      int rc = -EPERM;
>      struct avc_audit_data ad;
> -    u32 dperm = flask_iommu_resource_use_perm(d);
> +    u32 dperm;
>
>      if ( !d )
>          return flask_test_assign_device(machine_bdf);
>
> +    dperm = flask_iommu_resource_use_perm(d);
> +
>      rc = current_has_perm(d, SECCLASS_RESOURCE, RESOURCE__ADD);
>      if ( rc )
>          return rc;
> @@ -1355,11 +1357,13 @@ static int flask_assign_dtdevice(struct domain *d, const char *dtpath)
>      u32 dsid, rsid;
>      int rc = -EPERM;
>      struct avc_audit_data ad;
> -    u32 dperm = flask_iommu_resource_use_perm(d);
> +    u32 dperm;
>
>      if ( !d )
>          return flask_test_assign_dtdevice(dtpath);
>
> +    dperm = flask_iommu_resource_use_perm(d);
> +
>      rc = current_has_perm(d, SECCLASS_RESOURCE, RESOURCE__ADD);
>      if ( rc )
>          return rc;
> --
> 2.11.0
>

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Re: [Xen-devel] [PATCH for-4.13] xen/xsm: flask: Prevent NULL deference in flask_assign_{, dt}device()

[Jürgen Groß]

On 04.10.19 18:42, Julien Grall wrote:
> flask_assign_{, dt}device() may be used to check whether you can test if
> a device is assigned. In this case, the domain will be NULL.
> 
> However, flask_iommu_resource_use_perm() will be called and may end up
> to deference a NULL pointer. This can be prevented by moving the call
> after we check the validity for the domain pointer.
> 
> Coverity-ID: 1486741
> Fixes: 71e617a6b8 ('use is_iommu_enabled() where appropriate...')
> Signed-off-by: Julien Grall <julien.grall@arm.com>

Release-acked-by: Juergen Gross <jgross@suse.com>


Juergen

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Re: [Xen-devel] [PATCH for-4.13] xen/xsm: flask: Prevent NULL deference in flask_assign_{, dt}device()

[Artem Mygaiev]

Hi Julien

On Fri, 2019-10-04 at 17:42 +0100, Julien Grall wrote:
> flask_assign_{, dt}device() may be used to check whether you can test
> if
> a device is assigned. In this case, the domain will be NULL.
> 
> However, flask_iommu_resource_use_perm() will be called and may end
> up
> to deference a NULL pointer. This can be prevented by moving the call
> after we check the validity for the domain pointer.
> 
> Coverity-ID: 1486741

The correct CID is 1486742

> Fixes: 71e617a6b8 ('use is_iommu_enabled() where appropriate...')
> Signed-off-by: Julien Grall <
> julien.grall@arm.com
> >
> ---
>  xen/xsm/flask/hooks.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
> index 3b30827764..cf7f25cda2 100644
> --- a/xen/xsm/flask/hooks.c
> +++ b/xen/xsm/flask/hooks.c
> @@ -1296,11 +1296,13 @@ static int flask_assign_device(struct domain
> *d, uint32_t machine_bdf)
>      u32 dsid, rsid;
>      int rc = -EPERM;
>      struct avc_audit_data ad;
> -    u32 dperm = flask_iommu_resource_use_perm(d);
> +    u32 dperm;
>  
>      if ( !d )
>          return flask_test_assign_device(machine_bdf);
>  
> +    dperm = flask_iommu_resource_use_perm(d);
> +
>      rc = current_has_perm(d, SECCLASS_RESOURCE, RESOURCE__ADD);
>      if ( rc )
>          return rc;
> @@ -1355,11 +1357,13 @@ static int flask_assign_dtdevice(struct
> domain *d, const char *dtpath)
>      u32 dsid, rsid;
>      int rc = -EPERM;
>      struct avc_audit_data ad;
> -    u32 dperm = flask_iommu_resource_use_perm(d);
> +    u32 dperm;
>  
>      if ( !d )
>          return flask_test_assign_dtdevice(dtpath);
>  
> +    dperm = flask_iommu_resource_use_perm(d);
> +
>      rc = current_has_perm(d, SECCLASS_RESOURCE, RESOURCE__ADD);
>      if ( rc )
>          return rc;
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Re: [Xen-devel] [PATCH for-4.13] xen/xsm: flask: Prevent NULL deference in flask_assign_{, dt}device()

[Julien Grall]

On 09/10/2019 12:57, Artem Mygaiev wrote:
> Hi Julien

Hi,

> On Fri, 2019-10-04 at 17:42 +0100, Julien Grall wrote:
>> flask_assign_{, dt}device() may be used to check whether you can test
>> if
>> a device is assigned. In this case, the domain will be NULL.
>>
>> However, flask_iommu_resource_use_perm() will be called and may end
>> up
>> to deference a NULL pointer. This can be prevented by moving the call
>> after we check the validity for the domain pointer.
>>
>> Coverity-ID: 1486741
> 
> The correct CID is 1486742

Hmmm yes. The coverity report e-mail is a bit confusing to read.

However, I have already committed the patch so we will have to leave with it :(.

Cheers,

-- 
Julien Grall

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Re: [Xen-devel] [PATCH for-4.13] xen/xsm: flask: Prevent NULL deference in flask_assign_{, dt}device()

[Artem Mygaiev]

Hi,

On Thu, 2019-10-10 at 15:48 +0100, Julien Grall wrote:
> 
> On 09/10/2019 12:57, Artem Mygaiev wrote:
> > Hi Julien
> 
> Hi,
> 
> > On Fri, 2019-10-04 at 17:42 +0100, Julien Grall wrote:
> > > flask_assign_{, dt}device() may be used to check whether you can test
> > > if
> > > a device is assigned. In this case, the domain will be NULL.
> > > 
> > > However, flask_iommu_resource_use_perm() will be called and may end
> > > up
> > > to deference a NULL pointer. This can be prevented by moving the call
> > > after we check the validity for the domain pointer.
> > > 
> > > Coverity-ID: 1486741
> > 
> > The correct CID is 1486742
> 
> Hmmm yes. The coverity report e-mail is a bit confusing to read.
> 
> However, I have already committed the patch so we will have to leave with it :(.
> 

I guess the solution could be to fix another one and make a proper
commit comment with cross-reference :)

> Cheers,
> 
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