[PATCH] audit: return on memory error to avoid null pointer dereference

[PATCH] audit: return on memory error to avoid null pointer dereference

[Richard Guy Briggs]

If there is a memory allocation error when trying to change an audit
kernel feature value, the ignored allocation error will trigger a NULL
pointer dereference oops on subsequent use of that pointer.  Return
instead.

Passes audit-testsuite.
See: https://github.com/linux-audit/audit-kernel/issues/76
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
---
 kernel/audit.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/audit.c b/kernel/audit.c
index 5c25449..2de74be 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1059,6 +1059,8 @@ static void audit_log_feature_change(int which, u32 old_feature, u32 new_feature
 		return;
 
 	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_FEATURE_CHANGE);
+	if (!ab)
+		return;
 	audit_log_task_info(ab, current);
 	audit_log_format(ab, " feature=%s old=%u new=%u old_lock=%u new_lock=%u res=%d",
 			 audit_feature_names[which], !!old_feature, !!new_feature,
-- 
1.8.3.1

Re: [PATCH] audit: return on memory error to avoid null pointer dereference

[Paul Moore]

On Wed, Feb 21, 2018 at 4:30 AM, Richard Guy Briggs <rgb@redhat.com> wrote:
> If there is a memory allocation error when trying to change an audit
> kernel feature value, the ignored allocation error will trigger a NULL
> pointer dereference oops on subsequent use of that pointer.  Return
> instead.
>
> Passes audit-testsuite.
> See: https://github.com/linux-audit/audit-kernel/issues/76
> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> ---
>  kernel/audit.c | 2 ++
>  1 file changed, 2 insertions(+)

Thanks, merged.

In the future a "[PATCH v2]" prefix would be appreciated for patches
like this, it makes things a little easier in my inbox.

> diff --git a/kernel/audit.c b/kernel/audit.c
> index 5c25449..2de74be 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -1059,6 +1059,8 @@ static void audit_log_feature_change(int which, u32 old_feature, u32 new_feature
>                 return;
>
>         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_FEATURE_CHANGE);
> +       if (!ab)
> +               return;
>         audit_log_task_info(ab, current);
>         audit_log_format(ab, " feature=%s old=%u new=%u old_lock=%u new_lock=%u res=%d",
>                          audit_feature_names[which], !!old_feature, !!new_feature,
> --
> 1.8.3.1

-- 
paul moore
www.paul-moore.com

Re: [PATCH] audit: return on memory error to avoid null pointer dereference

[Paul Moore]

On Wed, Feb 21, 2018 at 6:49 PM, Paul Moore <paul@paul-moore.com> wrote:
> On Wed, Feb 21, 2018 at 4:30 AM, Richard Guy Briggs <rgb@redhat.com> wrote:
>> If there is a memory allocation error when trying to change an audit
>> kernel feature value, the ignored allocation error will trigger a NULL
>> pointer dereference oops on subsequent use of that pointer.  Return
>> instead.
>>
>> Passes audit-testsuite.
>> See: https://github.com/linux-audit/audit-kernel/issues/76
>> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
>> ---
>>  kernel/audit.c | 2 ++
>>  1 file changed, 2 insertions(+)
>
> Thanks, merged.
>
> In the future a "[PATCH v2]" prefix would be appreciated for patches
> like this, it makes things a little easier in my inbox.

After merging this I went through all the other callers to see if they
suffered the same mistake and everyone except for IMA was checking the
returned pointer for NULL.  Upon looking at the IMA code, and the
audit code which is called, I realized we are actually "ok" as
audit_log_task_info(), audit_log_format(), audit_log_end(), and others
all check for a NULL audit_buffer at the very top of the functions.
I'm going to leave this patch merged, it's a good practice after all,
but I don't believe that unpatched systems are in any danger of
oops'ing here.

>> diff --git a/kernel/audit.c b/kernel/audit.c
>> index 5c25449..2de74be 100644
>> --- a/kernel/audit.c
>> +++ b/kernel/audit.c
>> @@ -1059,6 +1059,8 @@ static void audit_log_feature_change(int which, u32 old_feature, u32 new_feature
>>                 return;
>>
>>         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_FEATURE_CHANGE);
>> +       if (!ab)
>> +               return;
>>         audit_log_task_info(ab, current);
>>         audit_log_format(ab, " feature=%s old=%u new=%u old_lock=%u new_lock=%u res=%d",
>>                          audit_feature_names[which], !!old_feature, !!new_feature,
>> --
>> 1.8.3.1

-- 
paul moore
www.paul-moore.com

Re: [PATCH] audit: return on memory error to avoid null pointer dereference

[Eric Paris]

I think if we went back and looked at history we'd see that all of the
code originally had none of the if(!ab) checks after allocation and
they just sorta slowly crept in over time. I prefer this pattern, but
it used to be the opposite everywhere.


On Wed, 2018-02-21 at 19:02 -0500, Paul Moore wrote:
> On Wed, Feb 21, 2018 at 6:49 PM, Paul Moore <paul@paul-moore.com>
> wrote:
> > On Wed, Feb 21, 2018 at 4:30 AM, Richard Guy Briggs <rgb@redhat.com
> > > wrote:
> > > If there is a memory allocation error when trying to change an
> > > audit
> > > kernel feature value, the ignored allocation error will trigger a
> > > NULL
> > > pointer dereference oops on subsequent use of that
> > > pointer.  Return
> > > instead.
> > > 
> > > Passes audit-testsuite.
> > > See: https://github.com/linux-audit/audit-kernel/issues/76
> > > Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> > > ---
> > >  kernel/audit.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > 
> > Thanks, merged.
> > 
> > In the future a "[PATCH v2]" prefix would be appreciated for
> > patches
> > like this, it makes things a little easier in my inbox.
> 
> After merging this I went through all the other callers to see if
> they
> suffered the same mistake and everyone except for IMA was checking
> the
> returned pointer for NULL.  Upon looking at the IMA code, and the
> audit code which is called, I realized we are actually "ok" as
> audit_log_task_info(), audit_log_format(), audit_log_end(), and
> others
> all check for a NULL audit_buffer at the very top of the functions.
> I'm going to leave this patch merged, it's a good practice after all,
> but I don't believe that unpatched systems are in any danger of
> oops'ing here.
> 
> > > diff --git a/kernel/audit.c b/kernel/audit.c
> > > index 5c25449..2de74be 100644
> > > --- a/kernel/audit.c
> > > +++ b/kernel/audit.c
> > > @@ -1059,6 +1059,8 @@ static void audit_log_feature_change(int
> > > which, u32 old_feature, u32 new_feature
> > >                 return;
> > > 
> > >         ab = audit_log_start(NULL, GFP_KERNEL,
> > > AUDIT_FEATURE_CHANGE);
> > > +       if (!ab)
> > > +               return;
> > >         audit_log_task_info(ab, current);
> > >         audit_log_format(ab, " feature=%s old=%u new=%u
> > > old_lock=%u new_lock=%u res=%d",
> > >                          audit_feature_names[which],
> > > !!old_feature, !!new_feature,
> > > --
> > > 1.8.3.1
> 
> 

Re: [PATCH] audit: return on memory error to avoid null pointer dereference

[Richard Guy Briggs]

On 2018-02-21 19:02, Paul Moore wrote:
> On Wed, Feb 21, 2018 at 6:49 PM, Paul Moore <paul@paul-moore.com> wrote:
> > On Wed, Feb 21, 2018 at 4:30 AM, Richard Guy Briggs <rgb@redhat.com> wrote:
> >> If there is a memory allocation error when trying to change an audit
> >> kernel feature value, the ignored allocation error will trigger a NULL
> >> pointer dereference oops on subsequent use of that pointer.  Return
> >> instead.
> >>
> >> Passes audit-testsuite.
> >> See: https://github.com/linux-audit/audit-kernel/issues/76
> >> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> >> ---
> >>  kernel/audit.c | 2 ++
> >>  1 file changed, 2 insertions(+)
> >
> > Thanks, merged.
> >
> > In the future a "[PATCH v2]" prefix would be appreciated for patches
> > like this, it makes things a little easier in my inbox.

(Sorry, forgot in haste to get that fixed one out...)

> After merging this I went through all the other callers to see if they
> suffered the same mistake and everyone except for IMA was checking the
> returned pointer for NULL.  Upon looking at the IMA code, and the
> audit code which is called, I realized we are actually "ok" as
> audit_log_task_info(), audit_log_format(), audit_log_end(), and others
> all check for a NULL audit_buffer at the very top of the functions.
> I'm going to leave this patch merged, it's a good practice after all,
> but I don't believe that unpatched systems are in any danger of
> oops'ing here.

On review, agreed.  My ctags/cscope DBs need regeneration, so I hadn't
noticed that the functions to which I was led weren't the ones I was
seeking, and while these three do check, not all functions that
accept a struct audit_buffer pointer parameter don't check for NULL.
Now that I check, I only find audit_expand (whose callers are all
protected) and audit_log_d_path (whose callers all appear to be
protected), the latter of which I've spent a bit of time staring at of
late (ghak8, ghak21...).

We're ok.

> >> diff --git a/kernel/audit.c b/kernel/audit.c
> >> index 5c25449..2de74be 100644
> >> --- a/kernel/audit.c
> >> +++ b/kernel/audit.c
> >> @@ -1059,6 +1059,8 @@ static void audit_log_feature_change(int which, u32 old_feature, u32 new_feature
> >>                 return;
> >>
> >>         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_FEATURE_CHANGE);
> >> +       if (!ab)
> >> +               return;
> >>         audit_log_task_info(ab, current);
> >>         audit_log_format(ab, " feature=%s old=%u new=%u old_lock=%u new_lock=%u res=%d",
> >>                          audit_feature_names[which], !!old_feature, !!new_feature,
> >> --
> >> 1.8.3.1
> 
> -- 
> paul moore
> www.paul-moore.com

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635

[PATCH] audit: return on memory error to avoid null pointer dereference

[Richard Guy Briggs]

If there is a memory allocation error when trying to change an audit
kernel feature value, the ignored allocation error will trigger a NULL
pointer dereference oops on subsequent use of that pointer.  Return
instead.

See: https://github.com/linux-audit/audit-kernel/issues/76
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
---
 kernel/audit.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/audit.c b/kernel/audit.c
index 196d327..31cb11d 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1063,6 +1063,8 @@ static void audit_log_feature_change(int which, u32 old_feature, u32 new_feature
 		return;
 
 	ab = audit_log_start(context, GFP_KERNEL, AUDIT_FEATURE_CHANGE);
+	if (!ab)
+		return;
 	audit_log_task_info(ab, current);
 	audit_log_format(ab, " feature=%s old=%u new=%u old_lock=%u new_lock=%u res=%d",
 			 audit_feature_names[which], !!old_feature, !!new_feature,
-- 
1.8.3.1

Re: [PATCH] audit: return on memory error to avoid null pointer dereference

[Richard Guy Briggs]

On 2018-02-21 01:47, Richard Guy Briggs wrote:
> If there is a memory allocation error when trying to change an audit
> kernel feature value, the ignored allocation error will trigger a NULL
> pointer dereference oops on subsequent use of that pointer.  Return
> instead.
> 
> See: https://github.com/linux-audit/audit-kernel/issues/76
> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>

Self-NACK.  It was based on local development and won't compile on
upstream.  Fix pending.

> ---
>  kernel/audit.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 196d327..31cb11d 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -1063,6 +1063,8 @@ static void audit_log_feature_change(int which, u32 old_feature, u32 new_feature
>  		return;
>  
>  	ab = audit_log_start(context, GFP_KERNEL, AUDIT_FEATURE_CHANGE);
> +	if (!ab)
> +		return;
>  	audit_log_task_info(ab, current);
>  	audit_log_format(ab, " feature=%s old=%u new=%u old_lock=%u new_lock=%u res=%d",
>  			 audit_feature_names[which], !!old_feature, !!new_feature,
> -- 
> 1.8.3.1
> 

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635