If 'n' is so large that it's negative, we might wrap around and mistakenly
think that the copy is OK when it's not. Such a copy would probably
crash, but just doing the arithmetic in a more simple way lets us detect
and refuse this case.
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
mm/usercopy.c | 19 +++++++++----------
1 file changed, 9 insertions(+), 10 deletions(-)
diff --git a/mm/usercopy.c b/mm/usercopy.c
index 31deee7dd2f5..ff16083cf1c8 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -162,20 +162,18 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
bool to_user)
{
uintptr_t addr = (uintptr_t)ptr;
+ unsigned long offset;
struct folio *folio;
if (is_kmap_addr(ptr)) {
- unsigned long page_end = addr | (PAGE_SIZE - 1);
-
- if (addr + n - 1 > page_end)
- usercopy_abort("kmap", NULL, to_user,
- offset_in_page(ptr), n);
+ offset = offset_in_page(ptr);
+ if (n > PAGE_SIZE - offset)
+ usercopy_abort("kmap", NULL, to_user, offset, n);
return;
}
if (is_vmalloc_addr(ptr)) {
struct vmap_area *area = find_vmap_area(addr);
- unsigned long offset;
if (!area) {
usercopy_abort("vmalloc", "no area", to_user, 0, n);
@@ -184,9 +182,10 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
/* XXX: We should also abort for free vmap_areas */
- offset = addr - area->va_start;
- if (addr + n > area->va_end)
+ if (n > area->va_end - addr) {
+ offset = addr - area->va_start;
usercopy_abort("vmalloc", NULL, to_user, offset, n);
+ }
return;
}
@@ -199,8 +198,8 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
/* Check slab allocator for flags and size. */
__check_heap_object(ptr, n, folio_slab(folio), to_user);
} else if (folio_test_large(folio)) {
- unsigned long offset = ptr - folio_address(folio);
- if (offset + n > folio_size(folio))
+ offset = ptr - folio_address(folio);
+ if (n > folio_size(folio) - offset)
usercopy_abort("page alloc", NULL, to_user, offset, n);
}
}
--
2.35.1
