[PATCH v4 1/4] mm/gup: fix wrongly calculated returned value in fault_in_safe_writeable()

Baoquan He
2025-04-10T03:57:36Z

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@redhat.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