[PATCH] selinux: tracer SID fix

Fix SELinux to not reset the tracer SID when the child is already being
traced, since selinux_ptrace is also called by proc for access checking
outside of the context of a ptrace attach.

Signed-off-by:  Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: James Morris <jmorris@namei.org>
Acked-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

security/selinux/hooks.c

@@ -1262,7 +1262,7 @@ static int selinux_ptrace(struct task_struct *parent, struct task_struct *child)
 
 	rc = task_has_perm(parent, child, PROCESS__PTRACE);
 	/* Save the SID of the tracing process for later use in apply_creds. */
-	if (!rc)
+	if (!(child->ptrace & PT_PTRACED) && !rc)
 		csec->ptrace_sid = psec->sid;
 	return rc;
 }