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.

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

[Stephen Smalley]

On Wed, Jun 10, 2020 at 2:10 PM  wrote:
>
> From: Tom Rix 
>
> 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 
> ---
>  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.

[PATCH 1/1] selinux: fix double free

[trix]

From: Tom Rix 

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 
---
 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