From 8c03ebd7cdc06bd0d2fecb4d1a609ef1dbb7d0aa Mon Sep 17 00:00:00 2001 From: Baoquan He Date: Thu, 10 Apr 2025 11:57:14 +0800 Subject: [PATCH] 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 calculates the size of the handled range with 'uaddr - start'. Fix it here. Andreas said: : In gfs2, fault_in_iov_iter_writeable() is used in : gfs2_file_direct_read() and gfs2_file_read_iter(), so this potentially : affects buffered as well as direct reads. This bug could cause those : gfs2 functions to spin in a loop. Link: https://lkml.kernel.org/r/20250410035717.473207-1-bhe@redhat.com Link: https://lkml.kernel.org/r/20250410035717.473207-2-bhe@redhat.com Signed-off-by: Baoquan He Fixes: fe673d3f5bf1 ("mm: gup: make fault_in_safe_writeable() use fixup_user_fault()") Reviewed-by: Oscar Salvador Acked-by: David Hildenbrand Cc: Andreas Gruenbacher Cc: Yanjun.Zhu Cc: Signed-off-by: Andrew Morton --- 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); -- 2.49.0