FAILED: patch "[PATCH] s390/mm: fix BUG_ON in crst_table_upgrade" failed to apply to 4.12-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 8ab867cb0806a8e195de161fd8883a0578d1d050 Mon Sep 17 00:00:00 2001
From: Martin Schwidefsky <schwidefsky@de.ibm.com>
Date: Thu, 31 Aug 2017 13:18:22 +0200
Subject: [PATCH] s390/mm: fix BUG_ON in crst_table_upgrade

A 31-bit compat process can force a BUG_ON in crst_table_upgrade
with specific, invalid mmap calls, e.g.

   mmap((void*) 0x7fff8000, 0x10000, 3, 32, -1, 0)

The arch_get_unmapped_area[_topdown] functions miss an if condition
in the decision to do a page table upgrade.

Fixes: 9b11c7912d00 ("s390/mm: simplify arch_get_unmapped_area[_topdown]")
Cc: <stable@vger.kernel.org>  # v4.12+
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
index 2e10d2b8ad35..5bea139517a2 100644
--- a/arch/s390/mm/mmap.c
+++ b/arch/s390/mm/mmap.c
@@ -119,7 +119,8 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
 		return addr;
 
 check_asce_limit:
-	if (addr + len > current->mm->context.asce_limit) {
+	if (addr + len > current->mm->context.asce_limit &&
+	    addr + len <= TASK_SIZE) {
 		rc = crst_table_upgrade(mm, addr + len);
 		if (rc)
 			return (unsigned long) rc;
@@ -183,7 +184,8 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 	}
 
 check_asce_limit:
-	if (addr + len > current->mm->context.asce_limit) {
+	if (addr + len > current->mm->context.asce_limit &&
+	    addr + len <= TASK_SIZE) {
 		rc = crst_table_upgrade(mm, addr + len);
 		if (rc)
 			return (unsigned long) rc;