2020-06-10 20:18:05

by Tom Rix

Subject: [PATCH 0/1] selinux: fix double free

From: Tom Rix <[email protected]>

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

2020-06-10 20:19:03

by Tom Rix

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

From: Tom Rix <[email protected]>

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 <[email protected]>
---
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

2020-06-10 20:20:07

by Stephen Smalley

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

On Wed, Jun 10, 2020 at 2:10 PM <[email protected]> wrote:
>
> From: Tom Rix <[email protected]>
>
> 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 <[email protected]>
> ---
> 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.

2020-06-10 20:22:03

by Tom Rix

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

>> +++ 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.