[PATCH] selinux: fix residual uses of current_security() for the SELinux blob

[Stephen Smalley]

On 9/4/19 10:32 AM, Stephen Smalley wrote:
> We need to use selinux_cred() to fetch the SELinux cred blob instead
> of directly using current->security or current_security().  There
> were a couple of lingering uses of current_security() in the SELinux code
> that were apparently missed during the earlier conversions. IIUC, this
> would only manifest as a bug if multiple security modules including
> SELinux are enabled and SELinux is not first in the lsm order.

To further qualify that, it would only manifest as a bug if multiple 
non-exclusive security modules that use the cred security blob are 
enabled and SELinux is not first.  I don't think that is possible today 
in existing upstream kernels since the cred blob-using modules are 
currently all exclusive and tomoyo switched to using the task security 
blob instead.  Obviously that will change if/when the stacking for AA 
support lands and may already be an issue in Ubuntu depending on what 
stacking patchsets and what lsm order it is using.

> After
> this change, there appear to be no other users of current_security()
> in-tree; perhaps we should remove it altogether.
> 
> Fixes: bbd3662a8348 ("Infrastructure management of the cred security blob")
> Signed-off-by: Stephen Smalley <sds at tycho.nsa.gov>
> ---
>   security/selinux/hooks.c          |  2 +-
>   security/selinux/include/objsec.h | 20 ++++++++++----------
>   2 files changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index d55571c585ff..f1b763eceef9 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3435,7 +3435,7 @@ static int selinux_inode_copy_up_xattr(const char *name)
>   static int selinux_kernfs_init_security(struct kernfs_node *kn_dir,
>   					struct kernfs_node *kn)
>   {
> -	const struct task_security_struct *tsec = current_security();
> +	const struct task_security_struct *tsec = selinux_cred(current_cred());
>   	u32 parent_sid, newsid, clen;
>   	int rc;
>   	char *context;
> diff --git a/security/selinux/include/objsec.h b/security/selinux/include/objsec.h
> index 231262d8eac9..d2e00c7595dd 100644
> --- a/security/selinux/include/objsec.h
> +++ b/security/selinux/include/objsec.h
> @@ -40,16 +40,6 @@ struct task_security_struct {
>   	u32 sockcreate_sid;	/* fscreate SID */
>   };
>   
> -/*
> - * get the subjective security ID of the current task
> - */
> -static inline u32 current_sid(void)
> -{
> -	const struct task_security_struct *tsec = current_security();
> -
> -	return tsec->sid;
> -}
> -
>   enum label_initialized {
>   	LABEL_INVALID,		/* invalid or not initialized */
>   	LABEL_INITIALIZED,	/* initialized */
> @@ -188,4 +178,14 @@ static inline struct ipc_security_struct *selinux_ipc(
>   	return ipc->security + selinux_blob_sizes.lbs_ipc;
>   }
>   
> +/*
> + * get the subjective security ID of the current task
> + */
> +static inline u32 current_sid(void)
> +{
> +	const struct task_security_struct *tsec = selinux_cred(current_cred());
> +
> +	return tsec->sid;
> +}
> +
>   #endif /* _SELINUX_OBJSEC_H_ */
>