[PATCH 0/1] selinux: fix double free

[PATCH 0/1] selinux: fix double free

[trix]

From: Tom Rix <trix@redhat.com>

Repo: linux-next
Tag: next-20200609

Running clang scan-view over linux-next uncovers many problem only a
few are memory related, this one looked like the most serious.

Tom Rix (1):
  selinux: fix double free

 security/selinux/ss/services.c | 4 ++++
 1 file changed, 4 insertions(+)

-- 
2.18.1

[PATCH 1/1] selinux: fix double free

[trix]

From: Tom Rix <trix@redhat.com>

Clang's static analysis tool reports these double free memory errors.

security/selinux/ss/services.c:2987:4: warning: Attempt to free released memory [unix.Malloc]
                        kfree(bnames[i]);
                        ^~~~~~~~~~~~~~~~
security/selinux/ss/services.c:2990:2: warning: Attempt to free released memory [unix.Malloc]
        kfree(bvalues);
        ^~~~~~~~~~~~~~

So improve the security_get_bools error handling by freeing these variables
and setting their return pointers to NULL and the return len to 0

Signed-off-by: Tom Rix <trix@redhat.com>
---
 security/selinux/ss/services.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 313919bd42f8..2dffae1feaff 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -2888,8 +2888,12 @@ int security_get_bools(struct selinux_state *state,
 	if (*names) {
 		for (i = 0; i < *len; i++)
 			kfree((*names)[i]);
+		kfree(names);
 	}
 	kfree(*values);
+	*len = 0;
+	*names = NULL;
+	*values = NULL;
 	goto out;
 }
 
-- 
2.18.1

Re: [PATCH 1/1] selinux: fix double free

[Stephen Smalley]

On Wed, Jun 10, 2020 at 2:10 PM <trix@redhat.com> wrote:
>
> From: Tom Rix <trix@redhat.com>
>
> Clang's static analysis tool reports these double free memory errors.
>
> security/selinux/ss/services.c:2987:4: warning: Attempt to free released memory [unix.Malloc]
>                         kfree(bnames[i]);
>                         ^~~~~~~~~~~~~~~~
> security/selinux/ss/services.c:2990:2: warning: Attempt to free released memory [unix.Malloc]
>         kfree(bvalues);
>         ^~~~~~~~~~~~~~
>
> So improve the security_get_bools error handling by freeing these variables
> and setting their return pointers to NULL and the return len to 0
>
> Signed-off-by: Tom Rix <trix@redhat.com>
> ---
>  security/selinux/ss/services.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> index 313919bd42f8..2dffae1feaff 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -2888,8 +2888,12 @@ int security_get_bools(struct selinux_state *state,
>         if (*names) {
>                 for (i = 0; i < *len; i++)
>                         kfree((*names)[i]);
> +               kfree(names);

kfree(*names)?

>         }
>         kfree(*values);
> +       *len = 0;
> +       *names = NULL;
> +       *values = NULL;
>         goto out;
>  }

Wondering if the caller handling ought to be changed too even though
this should avoid the problem.

Re: [PATCH 1/1] selinux: fix double free

[Tom Rix]

>> +++ b/security/selinux/ss/services.c
>> @@ -2888,8 +2888,12 @@ int security_get_bools(struct selinux_state *state,
>>         if (*names) {
>>                 for (i = 0; i < *len; i++)
>>                         kfree((*names)[i]);
>> +               kfree(names);
> kfree(*names)?

Yes.

> kfree(*values);
>> +       *len = 0;
>> +       *names = NULL;
>> +       *values = NULL;
>>         goto out;
>>  }
> Wondering if the caller handling ought to be changed too even though
> this should avoid the problem.
>
The poisoning of the returns avoids this.