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 2e10d2b8ad359607981ce381e27c3bf22e2e184d..5bea139517a2edc21dc50074d2c2e9a94dabb19e 100644 (file)
--- 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;