Fix prlimit64 for suid/sgid processes

Since check_prlimit_permission always fails in the case of SUID/GUID
processes, such processes are not able to read or set their own limits.
This commit changes this by assuming that process can always read/change
its own limits.
Signed-off-by: Kacper Kornet <kornet@camk.edu.pl>
Acked-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sys.c

@@ -1385,7 +1385,8 @@ static int check_prlimit_permission(struct task_struct *task)
 	const struct cred *cred = current_cred(), *tcred;
 
 	tcred = __task_cred(task);
-	if ((cred->uid != tcred->euid ||
+	if (current != task &&
+	    (cred->uid != tcred->euid ||
 	     cred->uid != tcred->suid ||
 	     cred->uid != tcred->uid  ||
 	     cred->gid != tcred->egid ||