[PATCH] lsm: setfsuid/setgsuid bug fix (4/4)

Patch from Jakub Jelínek <jakub@redhat.com>

Make sure setfsuid/setfsgid return values are right.  Before
include/linux/security.h was added, setfsuid/setfsgid always returned
old_fsuid, no matter if the fsuid was actually changed or not.

With the default security ops it seems to do the same, because both
security_task_setuid and security_task_post_setuid return 0, but these
are hooks which seem to return 0 on success, -errno on failure, so if
some non-default security hook is installed and ever returns -errno in
setfsuid/setfsgid, -errno will be returned from the syscall instead of
the expected old_fsuid.  This makes it hard to distinguish uids
0xfffff001 ..  0xffffffff from errors of security hooks.

kernel/sys.c

@@ -831,13 +831,11 @@ asmlinkage long sys_getresgid(gid_t *rgid, gid_t *egid, gid_t *sgid)
 asmlinkage long sys_setfsuid(uid_t uid)
 {
 	int old_fsuid;
-	int retval;
-
-	retval = security_task_setuid(uid, (uid_t)-1, (uid_t)-1, LSM_SETID_FS);
-	if (retval)
-		return retval;
 
 	old_fsuid = current->fsuid;
+	if (security_task_setuid(uid, (uid_t)-1, (uid_t)-1, LSM_SETID_FS))
+		return old_fsuid;
+
 	if (uid == current->uid || uid == current->euid ||
 	    uid == current->suid || uid == current->fsuid || 
 	    capable(CAP_SETUID))
@@ -850,9 +848,7 @@ asmlinkage long sys_setfsuid(uid_t uid)
 		current->fsuid = uid;
 	}
 
-	retval = security_task_post_setuid(old_fsuid, (uid_t)-1, (uid_t)-1, LSM_SETID_FS);
-	if (retval)
-		return retval;
+	security_task_post_setuid(old_fsuid, (uid_t)-1, (uid_t)-1, LSM_SETID_FS);
 
 	return old_fsuid;
 }
@@ -863,13 +859,11 @@ asmlinkage long sys_setfsuid(uid_t uid)
 asmlinkage long sys_setfsgid(gid_t gid)
 {
 	int old_fsgid;
-	int retval;
-
-	retval = security_task_setgid(gid, (gid_t)-1, (gid_t)-1, LSM_SETID_FS);
-	if (retval)
-		return retval;
 
 	old_fsgid = current->fsgid;
+	if (security_task_setgid(gid, (gid_t)-1, (gid_t)-1, LSM_SETID_FS))
+		return old_fsgid;
+
 	if (gid == current->gid || gid == current->egid ||
 	    gid == current->sgid || gid == current->fsgid || 
 	    capable(CAP_SETGID))