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From:   agordeev@linux.ibm.com
To:     linux-kernel@vger.kernel.org
Cc:     linux-mm@kvack.org, Alexander Gordeev <agordeev@linux.ibm.com>
Subject: [PATCH 1/2] mm/mmap.c: add more sanity checks to get_unmapped_area()
Date:   Mon, 23 Mar 2020 14:29:28 +0100
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From: 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.

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 d681a20eb4ea..a0fcb5ca0e06 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2168,12 +2168,13 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
 	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;
@@ -2194,7 +2195,7 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
 	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;
-- 
2.23.0