Commit 8c03ebd7 authored by Baoquan He's avatar Baoquan He Committed by Andrew Morton
Browse files

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: default avatarBaoquan He <bhe@redhat.com>
Fixes: fe673d3f ("mm: gup: make fault_in_safe_writeable() use fixup_user_fault()")
Reviewed-by: default avatarOscar Salvador <osalvador@suse.de>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Yanjun.Zhu <yanjun.zhu@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 86fba612

mm/gup.c

+2 −2
Original line number Diff line number Diff line
@@ -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);