[PATCH] selinux,smack: fix subjective/objective credential use mixups

[Casey Schaufler]

On 9/23/2021 8:47 AM, Paul Moore wrote:
> Jann Horn reported a problem with commit eb1231f73c4d ("selinux:
> clarify task subjective and objective credentials") where some LSM
> hooks were attempting to access the subjective credentials of a task
> other than the current task.  Generally speaking, it is not safe to
> access another task's subjective credentials and doing so can cause
> a number of problems.
>
> Further, while looking into the problem, I realized that Smack was
> suffering from a similar problem brought about by a similar commit
> 1fb057dcde11 ("smack: differentiate between subjective and objective
> task credentials").
>
> This patch addresses this problem by restoring the use of the task's
> objective credentials in those cases where the task is other than the
> current executing task.  Not only does this resolve the problem
> reported by Jann, it is arguably the correct thing to do in these
> cases.
>
> Cc: stable at vger.kernel.org
> Fixes: eb1231f73c4d ("selinux: clarify task subjective and objective credentials")
> Fixes: 1fb057dcde11 ("smack: differentiate between subjective and objective task credentials")
> Reported-by: Jann Horn <jannh at google.com>
> Acked-by: Eric W. Biederman <ebiederm at xmission.com>
> Signed-off-by: Paul Moore <paul at paul-moore.com>

Acked-by: Casey Schaufler <casey at schaufler-ca.com>

> ---
>  security/selinux/hooks.c   |    4 ++--
>  security/smack/smack_lsm.c |    4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 6517f221d52c..e7ebd45ca345 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2157,7 +2157,7 @@ static int selinux_ptrace_access_check(struct task_struct *child,
>  static int selinux_ptrace_traceme(struct task_struct *parent)
>  {
>  	return avc_has_perm(&selinux_state,
> -			    task_sid_subj(parent), task_sid_obj(current),
> +			    task_sid_obj(parent), task_sid_obj(current),
>  			    SECCLASS_PROCESS, PROCESS__PTRACE, NULL);
>  }
>  
> @@ -6222,7 +6222,7 @@ static int selinux_msg_queue_msgrcv(struct kern_ipc_perm *msq, struct msg_msg *m
>  	struct ipc_security_struct *isec;
>  	struct msg_security_struct *msec;
>  	struct common_audit_data ad;
> -	u32 sid = task_sid_subj(target);
> +	u32 sid = task_sid_obj(target);
>  	int rc;
>  
>  	isec = selinux_ipc(msq);
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index cacbe7518519..21a0e7c3b8de 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -2016,7 +2016,7 @@ static int smk_curacc_on_task(struct task_struct *p, int access,
>  				const char *caller)
>  {
>  	struct smk_audit_info ad;
> -	struct smack_known *skp = smk_of_task_struct_subj(p);
> +	struct smack_known *skp = smk_of_task_struct_obj(p);
>  	int rc;
>  
>  	smk_ad_init(&ad, caller, LSM_AUDIT_DATA_TASK);
> @@ -3480,7 +3480,7 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
>   */
>  static int smack_getprocattr(struct task_struct *p, char *name, char **value)
>  {
> -	struct smack_known *skp = smk_of_task_struct_subj(p);
> +	struct smack_known *skp = smk_of_task_struct_obj(p);
>  	char *cp;
>  	int slen;
>  
>