selinux,smack: fix subjective/objective credential use mixups

Jann Horn reported a problem with commit eb1231f ("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
1fb057d ("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: [email protected]
Fixes: eb1231f ("selinux: clarify task subjective and objective credentials")
Fixes: 1fb057d ("smack: differentiate between subjective and objective task credentials")
Reported-by: Jann Horn <[email protected]>
Acked-by: Eric W. Biederman <[email protected]>
Acked-by: Casey Schaufler <[email protected]>
Signed-off-by: Paul Moore <[email protected]>

Author: pcmoore

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);

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;