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usercopy: Make usercopy resilient against ridiculously large copies

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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@infradead.org>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Tested-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220612213227.3881769-4-willy@infradead.org
This commit is contained in:
Matthew Wilcox (Oracle) 2022-06-12 22:32:27 +01:00 committed by Kees Cook
parent 35fb9ae4aa
commit 1dfbe9fcda
1 changed files with 9 additions and 10 deletions
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19
mm/usercopy.c
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@ -162,27 +162,26 @@ 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);
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;
}
@ -195,8 +194,8 @@ 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);
}
}