On 10/21/2024 4:39 PM, Paul Moore wrote:
> On Oct 14, 2024 Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
>> Verify that the LSM releasing the secctx is the LSM that
>> allocated it. This was not necessary when only one LSM could
>> create a secctx, but once there can be more than one it is.
>>
>> Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
>> ---
>> security/apparmor/secid.c | 10 ++--------
>> security/selinux/hooks.c | 10 ++--------
>> 2 files changed, 4 insertions(+), 16 deletions(-)
>>
>> diff --git a/security/apparmor/secid.c b/security/apparmor/secid.c
>> index 5d92fc3ab8b4..974f802cbe5a 100644
>> --- a/security/apparmor/secid.c
>> +++ b/security/apparmor/secid.c
>> @@ -122,14 +122,8 @@ int apparmor_secctx_to_secid(const char *secdata, u32 seclen, u32 *secid)
>>
>> void apparmor_release_secctx(struct lsm_context *cp)
>> {
>> - /*
>> - * stacking scaffolding:
>> - * When it is possible for more than one LSM to provide a
>> - * release hook, do this check:
>> - * if (cp->id == LSM_ID_APPARMOR || cp->id == LSM_ID_UNDEF)
>> - */
>> -
>> - kfree(cp->context);
>> + if (cp->id == LSM_ID_APPARMOR)
>> + kfree(cp->context);
> Should we set cp->context to NULL too? One could argue that it's an
> unecessary assignment, given the cp->id checks, and they wouldn't be
> wrong, but considering the potential for a BPF LSM to do things with
> a lsm_context, I wonder if resetting the pointer to NULL is the
> smart thing to do.
Wouldn't hurt. I'll go ahead and add that. If a BPF LSM does anything
with a lsm_context we're likely to hear about the many issues quite
quickly.
>
> This obviously applies to the SELinux code (below) too.
>
>> }
>>
>> /**
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index 79776a5e651d..b9286c2c5efe 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -6640,14 +6640,8 @@ static int selinux_secctx_to_secid(const char *secdata, u32 seclen, u32 *secid)
>>
>> static void selinux_release_secctx(struct lsm_context *cp)
>> {
>> - /*
>> - * stacking scaffolding:
>> - * When it is possible for more than one LSM to provide a
>> - * release hook, do this check:
>> - * if (cp->id == LSM_ID_SELINUX || cp->id == LSM_ID_UNDEF)
>> - */
>> -
>> - kfree(cp->context);
>> + if (cp->id == LSM_ID_SELINUX)
>> + kfree(cp->context);
>> }
>>
>> static void selinux_inode_invalidate_secctx(struct inode *inode)
> --
> paul-moore.com
>
