[PATCH] mm, vmalloc: Fix a potential overflow bug in alloc_vmap_area

[Zhang Yanfei]

When searching a vmap area in the vmalloc space, we use
(addr + size - 1) to check if the value is less than addr, which
is an overflow. But we assign (addr + size) to vmap_area->va_end.

So if we come across the  below case:

(addr + size - 1) : not overflow
(addr + size)     : overflow

we will assign an overflow value (e.g 0) to vmap_area->va_end,
And this will trigger BUG in __insert_vmap_area, causing system
panic.

So using (addr + size) to check the overflow should be the correct
behaviour, not (addr + size - 1).

Reported-by: Ghennadi Procopciuc <unix140@xxxxxxxxx>
Signed-off-by: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx>
---
 mm/vmalloc.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d365724..d456560 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -388,12 +388,12 @@ nocache:
 		addr = ALIGN(first->va_end, align);
 		if (addr < vstart)
 			goto nocache;
-		if (addr + size - 1 < addr)
+		if (addr + size < addr)
 			goto overflow;
 
 	} else {
 		addr = ALIGN(vstart, align);
-		if (addr + size - 1 < addr)
+		if (addr + size < addr)
 			goto overflow;
 
 		n = vmap_area_root.rb_node;
@@ -420,7 +420,7 @@ nocache:
 		if (addr + cached_hole_size < first->va_start)
 			cached_hole_size = first->va_start - addr;
 		addr = ALIGN(first->va_end, align);
-		if (addr + size - 1 < addr)
+		if (addr + size < addr)
 			goto overflow;
 
 		if (list_is_last(&first->list, &vmap_area_list))
-- 
1.7.1


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