On Sat, Aug 26, 2017 at 12:11:24PM -0700, 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.
>
> Fixes: 70c3547e36f5c ("hugetlbfs: add hugetlbfs_fallocate()")
>
> cc: Eric Biggers <[email protected]>
> cc: Mike Kravetz <[email protected]>
>
> Signed-off-by: Nadav Amit <[email protected]>
> ---
> 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)
> --
This patch wasn't ever applied. Nadia, do you take patches for hugetlbfs, or
does this need to go through Andrew Morton?
Eric
