From 1b1cd27a90cfdeab5ca2d141c603a8f4591425f1 Mon Sep 17 00:00:00 2001 From: Nadav Amit Date: Wed, 29 Nov 2017 16:11:33 -0800 Subject: [PATCH] fs/hugetlbfs/inode.c: change put_page/unlock_page order in hugetlbfs_fallocate() hugetlfs_fallocate() currently performs put_page() before unlock_page(). This scenario opens a small time window, from the time the page is added to the page cache, until it is unlocked, in which the page might be removed from the page-cache by another core. If the page is removed during this time windows, it might cause a memory corruption, as the wrong page will be unlocked. It is arguable whether this scenario can happen in a real system, and there are several mitigating factors. The issue was found by code inspection (actually grep), and not by actually triggering the flow. Yet, since putting the page before unlocking is incorrect it should be fixed, if only to prevent future breakage or someone copy-pasting this code. Mike said: "I am of the opinion that this does not need to be sent to stable. Although the ordering is current code is incorrect, there is no way for this to be a problem with current locking. In addition, I verified that the perhaps bigger issue with sys_fadvise64(POSIX_FADV_DONTNEED) for hugetlbfs and other filesystems is addressed in f03c89d5a742 ("mm: fadvise: avoid fadvise for fs without backing device")" Link: http://lkml.kernel.org/r/20170826191124.51642-1-namit@vmware.com Fixes: 9c6bed61be5df ("hugetlbfs: add hugetlbfs_fallocate()") Signed-off-by: Nadav Amit Reviewed-by: Mike Kravetz Acked-by: Michal Hocko Cc: Eric Biggers Cc: Mike Kravetz Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/hugetlbfs/inode.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 1e76730aac0de..8a85f3f534465 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -639,11 +639,11 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset, mutex_unlock(&hugetlb_fault_mutex_table[hash]); /* - * page_put due to reference from alloc_huge_page() * unlock_page because locked by add_to_page_cache() + * page_put due to reference from alloc_huge_page() */ - put_page(page); unlock_page(page); + put_page(page); } if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size) -- 2.39.5