share_pool: Adjust the position of do_mmap checker

ascend inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4EUVI
CVE: NA

-------------------------------------------------

do_mmap checker should be put before MAP_FIXED.
Signed-off-by: NTang Yizhou <tangyizhou@huawei.com>
Reviewed-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

mm/mmap.c

@@ -2351,12 +2351,12 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	if (len > TASK_SIZE - mmap_min_addr)
 		return -ENOMEM;
 
-	if (flags & MAP_FIXED)
-		return addr;
-
 	if (sp_check_mmap_addr(addr, flags))
 		return -EINVAL;
 
+	if (flags & MAP_FIXED)
+		return addr;
+
 	if (addr) {
 		addr = PAGE_ALIGN(addr);
 
@@ -2405,12 +2405,12 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 	if (len > TASK_SIZE - mmap_min_addr)
 		return -ENOMEM;
 
-	if (flags & MAP_FIXED)
-		return addr;
-
 	if (sp_check_mmap_addr(addr, flags))
 		return -EINVAL;
 
+	if (flags & MAP_FIXED)
+		return addr;
+
 	/* requesting a specific address */
 	if (addr) {
 		addr = PAGE_ALIGN(addr);