Messages in this thread |  | | Date | Mon, 28 Aug 2017 15:46:45 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH] hugetlbfs: change put_page/unlock_page order in hugetlbfs_fallocate() |
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[CC Andrew]
On Sat 26-08-17 12:11:24, Nadav Amit wrote: > 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.
Even if this a theoretical problem it is definitely worth fixing because it is a anti-pattern of how the reference counted object should be treated.
> Fixes: 70c3547e36f5c ("hugetlbfs: add hugetlbfs_fallocate()") > > cc: Eric Biggers <ebiggers3@gmail.com> > cc: Mike Kravetz <mike.kravetz@oracle.com> > > Signed-off-by: Nadav Amit <namit@vmware.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Thanks!
> --- > 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 28d2753be094..9475fee79cee 100644 > --- a/fs/hugetlbfs/inode.c > +++ b/fs/hugetlbfs/inode.c > @@ -655,11 +655,11 @@ 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) > -- > 2.11.0
-- Michal Hocko SUSE Labs
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