On Thu, Sep 19, 2019 at 04:01:38PM -0500, Bill O'Donnell wrote:
> Guarantee zeroed memory buffers for cases where potential memory
> leak to disk can occur. In these cases, kmem_alloc is used and
> doesn't zero the buffer, opening the possibility of information
> leakage to disk.
>
> Use existing infrastucture (xfs_buf_allocate_memory) to obtain
> the already zeroed buffer from kernel memory.
>
> This solution avoids the performance issue that would occur if a
> wholesale change to replace kmem_alloc with kmem_zalloc was done.
>
> Signed-off-by: Bill O'Donnell <billodo@xxxxxxxxxx>
> ---
> v4: use __GFP_ZERO as part of gfp_mask (instead of KM_ZERO)
> v3: remove XBF_ZERO flag, and instead use XBF_READ flag only.
> v2: zeroed buffer not required for XBF_READ case. Correct placement
> and rename the XBF_ZERO flag.
>
> fs/xfs/xfs_buf.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 120ef99d09e8..5d0a68de5fa6 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -345,6 +345,15 @@ xfs_buf_allocate_memory(
> unsigned short page_count, i;
> xfs_off_t start, end;
> int error;
> + uint kmflag_mask = 0;
> +
> + /*
> + * assure zeroed buffer for non-read cases.
> + */
> + if (!(flags & XBF_READ)) {
> + kmflag_mask |= KM_ZERO;
> + gfp_mask |= __GFP_ZERO;
> + }
Jeez it feels grody to have to set two different flags variables just to
get __GFP_ZERO consistently but I'll run it through xfstests overnight.
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
>
> /*
> * for buffers that are contained within a single page, just allocate
> @@ -354,7 +363,8 @@ xfs_buf_allocate_memory(
> size = BBTOB(bp->b_length);
> if (size < PAGE_SIZE) {
> int align_mask = xfs_buftarg_dma_alignment(bp->b_target);
> - bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS);
> + bp->b_addr = kmem_alloc_io(size, align_mask,
> + KM_NOFS | kmflag_mask);
> if (!bp->b_addr) {
> /* low memory - use alloc_page loop instead */
> goto use_alloc_page;
> --
> 2.21.0
>
