drbd: detect modification of in-flight buffers

With data-integrity digest enabled, double-check on the sending side
for modifications by upper layers of buffers under write back,
so we can tell it appart from corruption on the "wire".

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

1 files changed, 27 insertions, 1 deletions

diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 6afb81f807bd..451fc36a85cb 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -2537,10 +2537,36 @@ int drbd_send_dblock(struct drbd_conf *mdev, struct drbd_request *req)
                 ok = drbd_send(mdev, mdev->data.socket, dgb, dgs, 0);
         }
         if (ok) {
-                if (mdev->net_conf->wire_protocol == DRBD_PROT_A)
+                /* For protocol A, we have to memcpy the payload into
+                 * socket buffers, as we may complete right away
+                 * as soon as we handed it over to tcp, at which point the data
+                 * pages may become invalid.
+                 *
+                 * For data-integrity enabled, we copy it as well, so we can be
+                 * sure that even if the bio pages may still be modified, it
+                 * won't change the data on the wire, thus if the digest checks
+                 * out ok after sending on this side, but does not fit on the
+                 * receiving side, we sure have detected corruption elsewhere.
+                 */
+                if (mdev->net_conf->wire_protocol == DRBD_PROT_A || dgs)
                         ok = _drbd_send_bio(mdev, req->master_bio);
                 else
                         ok = _drbd_send_zc_bio(mdev, req->master_bio);
+
+                /* double check digest, sometimes buffers have been modified in flight. */
+                if (dgs > 0 && dgs <= 64) {
+                        /* 64 byte, 512 bit, is the larges digest size
+                         * currently supported in kernel crypto. */
+                        unsigned char digest[64];
+                        drbd_csum_bio(mdev, mdev->integrity_w_tfm, req->master_bio, digest);
+                        if (memcmp(mdev->int_dig_out, digest, dgs)) {
+                                dev_warn(DEV,
+                                        "Digest mismatch, buffer modified by upper layers during write: %llus +%u\n",
+                                        (unsigned long long)req->sector, req->size);
+                        }
+                } /* else if (dgs > 64) {
+                     ... Be noisy about digest too large ...
+                } */
         }
 
         drbd_put_data_sock(mdev);