[PATCH v2] drbd: validate digest size in checksum resync and verify requests

[Yibo Liu <yiboliume@gmail.com>]

receive_DataRequest() sizes the digest buffer of P_CSUM_RS_REQUEST and
P_OV_REPLY packets from the length the peer puts in the packet header,
without checking it against the digest size of the negotiated csums-alg
or verify-alg. w_e_end_csum_rs_req() and w_e_end_ov_reply() later
memcmp() crypto_shash_digestsize() bytes of that buffer; the D_ASSERT()
on the size only logs a message.

A peer that sends a shorter digest thus causes a slab-out-of-bounds read
in the worker, and a peer that declares a huge length makes the receiver
attempt an oversized kmalloc() that triggers a page allocator warning.

  BUG: KASAN: slab-out-of-bounds in memcmp (lib/string.c:676)
  Read of size 8 at addr ff11000007b9d630 by task drbd_w_r0/601
  Call Trace:
   memcmp (lib/string.c:676)
   w_e_end_csum_rs_req (drivers/block/drbd/drbd_worker.c:1182)
   drbd_worker (drivers/block/drbd/drbd_worker.c:2189)
   drbd_thread_setup (drivers/block/drbd/drbd_main.c:314)
   kthread (kernel/kthread.c:436)
   ret_from_fork (arch/x86/kernel/process.c:158)
   ret_from_fork_asm (arch/x86/entry/entry_64.S:245)

  Allocated by task 605:
   __kmalloc_noprof (mm/slub.c:5439)
   receive_DataRequest (drivers/block/drbd/drbd_receiver.c:2715)
   drbd_receiver (drivers/block/drbd/drbd_receiver.c:5371)
   drbd_thread_setup (drivers/block/drbd/drbd_main.c:314)
   kthread (kernel/kthread.c:436)

Reject the packet and drop the connection unless the declared digest
length matches the digest size of the corresponding transform, or if
no such transform is configured.

Fixes: b411b3637fa7 ("The DRBD driver")
Cc: stable@vger.kernel.org
Reported-by: co+0845f49852fd568f@bugs.sh
Signed-off-by: Yibo Liu <yiboliume@gmail.com>
---
Changes in v2:
- Drop patch 1/2 (P_DATA_REPLY size check); this is now a single patch.
- Check the digest length only in receive_DataRequest(), before the
  buffer is allocated, and leave drbd_worker.c unchanged: with the exact
  size enforced on receive, the sizes compared in the worker always match.

v1: https://lore.kernel.org/all/20261015222800.85928-1-yiboliume@gmail.com/

 drivers/block/drbd/drbd_receiver.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 2135c14354a8..d45c4e68f83b 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -2711,7 +2711,17 @@ static int receive_DataRequest(struct drbd_connection *connection, struct packet
 		break;
 
 	case P_OV_REPLY:
-	case P_CSUM_RS_REQUEST:
+	case P_CSUM_RS_REQUEST: {
+		struct crypto_shash *tfm = pi->cmd == P_CSUM_RS_REQUEST ?
+			peer_device->connection->csums_tfm :
+			peer_device->connection->verify_tfm;
+
+		if (!tfm || pi->size != crypto_shash_digestsize(tfm)) {
+			drbd_err(device, "%s: unexpected digest size %u\n",
+				 cmdname(pi->cmd), pi->size);
+			goto out_free_e;
+		}
+
 		di = kmalloc(sizeof(*di) + pi->size, GFP_NOIO);
 		if (!di)
 			goto out_free_e;
@@ -2742,6 +2752,7 @@ static int receive_DataRequest(struct drbd_connection *connection, struct packet
 			goto submit_for_resync;
 		}
 		break;
+	}
 
 	case P_OV_REQUEST:
 		if (device->ov_start_sector == ~(sector_t)0 &&

base-commit: c03c1a14507dfaf8b856c2608f9ac216021fc222
-- 
2.34.1