[PATCH RESEND 1/2] mm/mmap.c: add more sanity checks to get_unmapped_area()

[Alexander Gordeev <agordeev@linux.ibm.com>]

Generic get_unmapped_area() function does sanity checks
of address and length of the area to be mapped. Yet, it
lacks checking against mmap_min_addr and mmap_end limits.

At the same time the default implementation of functions
arch_get_unmapped_area[_topdown]() and some architecture
callbacks do mmap_min_addr and mmap_end checks on its own.

Put additional checks into the generic code and do not let
architecture callbacks to get away with a possible area
outside of the allowed limits.

That could also relieve arch_get_unmapped_area[_topdown]()
callbacks of own address and length sanity checks.

CC: linux-mm@kvack.org
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
---
 mm/mmap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 0681bd5..5b22d47 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2208,12 +2208,13 @@ unsigned long vm_unmapped_area(struct vm_unmapped_area_info *info)
 	unsigned long (*get_area)(struct file *, unsigned long,
 				  unsigned long, unsigned long, unsigned long);
 
+	const unsigned long mmap_end = arch_get_mmap_end(addr);
 	unsigned long error = arch_mmap_check(addr, len, flags);
 	if (error)
 		return error;
 
 	/* Careful about overflows.. */
-	if (len > TASK_SIZE)
+	if (len > mmap_end - mmap_min_addr)
 		return -ENOMEM;
 
 	get_area = current->mm->get_unmapped_area;
@@ -2234,7 +2235,7 @@ unsigned long vm_unmapped_area(struct vm_unmapped_area_info *info)
 	if (IS_ERR_VALUE(addr))
 		return addr;
 
-	if (addr > TASK_SIZE - len)
+	if ((addr < mmap_min_addr) || (addr > mmap_end - len))
 		return -ENOMEM;
 	if (offset_in_page(addr))
 		return -EINVAL;
-- 
1.8.3.1