[patch 23/54] mm/mmap.c: add more sanity checks to get_unmapped_area()

[Andrew Morton <akpm@linux-foundation.org>]

From: Alexander Gordeev <agordeev@linux.ibm.com>
Subject: mm/mmap.c: add more sanity checks to get_unmapped_area()

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 their 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.

Link: http://lkml.kernel.org/r/d14f2cff3c891ef2c4b0337d737c6f04beacb124.1584958099.git.agordeev@linux.ibm.com
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mmap.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/mm/mmap.c~mm-mmapc-add-more-sanity-checks-to-get_unmapped_area
+++ a/mm/mmap.c
@@ -2193,12 +2193,13 @@ get_unmapped_area(struct file *file, uns
 	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;
@@ -2219,7 +2220,7 @@ get_unmapped_area(struct file *file, uns
 	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;
_