On Thu, Feb 02, 2023 at 10:38:49PM -0800, Andrew Morton wrote:
> This patch was dropped because it was merged into the mm-stable branch
> of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
I pick the worst time to find bugs in my own code.
>From cf8f62107c965eafc2fa9ad0f839269fcb11991d Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Date: Fri, 3 Feb 2023 16:28:40 -0500
Subject: [PATCH] mm: Fix memcpy_from_file_folio() integer underflow
If we have a HIGHMEM system with a large folio, 'offset' may be larger
than PAGE_SIZE, and so min_t will cap at 'len' instead of the intended
end-of-page. That can overflow into the next page which is likely to
be unmapped and fault, but could theoretically copy the wrong data.
Fixes: [no commit ID yet] ("mm: add memcpy_from_file_folio()")
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
include/linux/highmem.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 348701dae77f..b06254e76d99 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -431,9 +431,10 @@ static inline size_t memcpy_from_file_folio(char *to, struct folio *folio,
size_t offset = offset_in_folio(folio, pos);
char *from = kmap_local_folio(folio, offset);
- if (folio_test_highmem(folio))
+ if (folio_test_highmem(folio)) {
+ offset = offset_in_page(offset);
len = min_t(size_t, len, PAGE_SIZE - offset);
- else
+ } else
len = min(len, folio_size(folio) - offset);
memcpy(to, from, len);
--
2.35.1
