linux-kernel - [PATCH v4 1/4] mm/gup: fix wrongly calculated returned value in fault_in_safe

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Message-ID: <20250410035717.473207-2-bhe@redhat.com>
Date: Thu, 10 Apr 2025 11:57:14 +0800
From: Baoquan He <bhe@...hat.com>
To: linux-mm@...ck.org
Cc: akpm@...ux-foundation.org,
	david@...hat.com,
	osalvador@...e.de,
	yanjun.zhu@...ux.dev,
	linux-kernel@...r.kernel.org,
	Baoquan He <bhe@...hat.com>
Subject: [PATCH v4 1/4] mm/gup: fix wrongly calculated returned value in fault_in_safe_writeable()

Not like fault_in_readable() or fault_in_writeable(), in
fault_in_safe_writeable() local variable 'start' is increased page
by page to loop till the whole address range is handled. However,
it mistakenly calcalates the size of handled range with 'uaddr - start'.

Fix it here.

Signed-off-by: Baoquan He <bhe@...hat.com>
Fixes: fe673d3f5bf1 ("mm: gup: make fault_in_safe_writeable() use fixup_user_fault()")
---
 mm/gup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 92351e2fa876..84461d384ae2 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2207,8 +2207,8 @@ size_t fault_in_safe_writeable(const char __user *uaddr, size_t size)
 	} while (start != end);
 	mmap_read_unlock(mm);
 
-	if (size > (unsigned long)uaddr - start)
-		return size - ((unsigned long)uaddr - start);
+	if (size > start - (unsigned long)uaddr)
+		return size - (start - (unsigned long)uaddr);
 	return 0;
 }
 EXPORT_SYMBOL(fault_in_safe_writeable);
-- 
2.41.0