[PATCH net v1 0/4] net: devmem: fix RX and TX binding teardown on device unregistration

[PATCH net v1 0/4] net: devmem: fix RX and TX binding teardown on device unregistration

[Mina Almasry]

Fix two device-unregistration lifecycle bugs in devmem TCP bindings and
add netdevsim support plus selftests covering both RX and TX device
unregistration:

1. net: devmem: unmap dma_buf synchronously on queue uninstall
   Synchronously unmap and detach binding->attachment under binding->lock
   when the last RX queue is uninstalled in mp_dmabuf_devmem_uninstall(),
   preventing slab-use-after-free in dma_unmap_sg_attrs() when the netlink
   socket closes after dma_dev is freed.

2. net: devmem: detach TX bindings on NETDEV_UNREGISTER
   Add net_devmem_dev_unregister() on NETDEV_UNREGISTER to fully detach and
   unmap TX bindings when binding->dev unregisters, or clear binding->vdev
   alone when only a virtual device unregisters while binding->dev lives.

3. netdevsim: support devmem RX and TX bindings
   Enable PP_FLAG_DMA_MAP | PP_FLAG_ALLOW_UNREADABLE_NETMEM, 64-bit DMA mask
   on nsim_bus_dev, and NETMEM_TX_DMA on netdevsim so devmem RX/TX bindings
   can be exercised in software selftests.

4. selftests: net: add devmem RX and TX netdev unregister tests
   Add devmem_bind_rx_unregister_check and devmem_bind_tx_unregister_check
   to tools/testing/selftests/net/nl_netdev.py.

Cc: Tariq Toukan <tariqt@nvidia.com>
Cc: Kaifeng Wang <kaifengw@google.com>

Mina Almasry (4):
  net: devmem: unmap dma_buf synchronously on queue uninstall
  net: devmem: detach TX bindings on NETDEV_UNREGISTER
  netdevsim: support devmem RX and TX bindings
  selftests: net: add devmem RX and TX netdev unregister tests

 drivers/net/netdevsim/bus.c              |   1 +
 drivers/net/netdevsim/netdev.c           |  21 +++--
 net/core/devmem.c                        |  68 +++++++++++++-
 net/core/devmem.h                        |   5 ++
 net/core/netdev-genl.c                   |   1 +
 tools/testing/selftests/net/nl_netdev.py | 108 ++++++++++++++++++++++-
 6 files changed, 192 insertions(+), 12 deletions(-)


base-commit: af32da41b0327b9c6a37856ba82b6760d6c8d10e
-- 
2.56.0.385.gd3acb90ef8-goog

[PATCH net v1 1/4] net: devmem: unmap dma_buf synchronously on queue uninstall

[Mina Almasry]

When a bound net_device is unregistered while userspace still holds a
netlink or TCP socket reference on a devmem binding,
mp_dmabuf_devmem_uninstall() clears binding->dev to NULL so
netdev_nl_sock_priv_destroy() will not touch the unregistered
net_device, but leaves the dma_buf attachment mapped until
__net_devmem_dmabuf_binding_free() runs later on socket close.

Because dma_buf_attach() does not take a reference on dma_dev, device
removal frees dma_dev while the attachment is still mapped. Closing the
netlink socket afterwards triggers a slab use-after-free in
dma_unmap_sg_attrs():

  BUG: KASAN: slab-use-after-free in dma_unmap_sg_attrs+0x76/0x2b0
  Read of size 8 at addr ffff88810fae64b0 by task kworker/3:1/53
  Workqueue: events __net_devmem_dmabuf_binding_free
  Call Trace:
   dma_unmap_sg_attrs+0x76/0x2b0
   unmap_udmabuf+0x8e/0x100
   dma_buf_unmap_attachment+0x145/0x330
   dma_buf_unmap_attachment_unlocked+0x96/0x130
   __net_devmem_dmabuf_binding_free+0x156/0x2e0
  Freed by task 9:
   kfree+0x1b8/0x550
   nsim_bus_dev_release+0xe/0x60
   device_release+0xcf/0x250

Add net_devmem_dmabuf_binding_unmap() serialized under binding->lock
and null out binding->sgt and binding->attachment after unmapping so
unmapping is idempotent across queue uninstall and deferred binding
destruction. Call it synchronously when the last bound RX queue is
uninstalled in mp_dmabuf_devmem_uninstall().

Fixes: f8350a4358fc ("net: page_pool: add a mp hook to unregister_netdevice*")
Fixes: 0afc44d8cdf6 ("net: devmem: fix kernel panic when netlink socket close after module unload")
Cc: Taehee Yoo <ap420073@gmail.com>
Cc: Stanislav Fomichev <sdf@fomichev.me>
Cc: Tariq Toukan <tariqt@nvidia.com>
Cc: Kaifeng Wang <kaifengw@google.com>
Signed-off-by: Mina Almasry <almasrymina@google.com>
---
 net/core/devmem.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/net/core/devmem.c b/net/core/devmem.c
index f4d60654ce7fd..5e4070b82df44 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c
@@ -58,6 +58,21 @@ static void net_devmem_dmabuf_binding_release(struct percpu_ref *ref)
 	schedule_work(&binding->unbind_w);
 }
 
+static void
+net_devmem_dmabuf_binding_unmap(struct net_devmem_dmabuf_binding *binding)
+{
+	lockdep_assert_held(&binding->lock);
+
+	if (!binding->sgt)
+		return;
+
+	dma_buf_unmap_attachment_unlocked(binding->attachment, binding->sgt,
+					  binding->direction);
+	dma_buf_detach(binding->dmabuf, binding->attachment);
+	binding->sgt = NULL;
+	binding->attachment = NULL;
+}
+
 void __net_devmem_dmabuf_binding_free(struct work_struct *wq)
 {
 	struct net_devmem_dmabuf_binding *binding = container_of(wq, typeof(*binding), unbind_w);
@@ -74,9 +89,10 @@ void __net_devmem_dmabuf_binding_free(struct work_struct *wq)
 		  size, avail))
 		gen_pool_destroy(binding->chunk_pool);
 
-	dma_buf_unmap_attachment_unlocked(binding->attachment, binding->sgt,
-					  binding->direction);
-	dma_buf_detach(binding->dmabuf, binding->attachment);
+	mutex_lock(&binding->lock);
+	net_devmem_dmabuf_binding_unmap(binding);
+	mutex_unlock(&binding->lock);
+
 	dma_buf_put(binding->dmabuf);
 	xa_destroy(&binding->bound_rxqs);
 	percpu_ref_exit(&binding->ref);
@@ -535,6 +551,7 @@ static void mp_dmabuf_devmem_uninstall(void *mp_priv,
 				mutex_lock(&binding->lock);
 				ASSERT_EXCLUSIVE_WRITER(binding->dev);
 				WRITE_ONCE(binding->dev, NULL);
+				net_devmem_dmabuf_binding_unmap(binding);
 				mutex_unlock(&binding->lock);
 			}
 			break;
-- 
2.56.0.385.gd3acb90ef8-goog

[PATCH net v1 2/4] net: devmem: detach TX bindings on NETDEV_UNREGISTER

[Mina Almasry]

TX devmem bindings (NETDEV_CMD_BIND_TX) have no bound RX queues, so
mp_dmabuf_devmem_uninstall() never runs when binding->dev or
binding->vdev unregisters. As a result, binding->dev and binding->vdev
dangle pointing to freed struct net_device memory, and the dma_buf
remains attached and mapped after device removal.

Closing the netlink socket after netdev unregistration dereferences the
freed struct net_device in netdev_nl_sock_priv_destroy():

  BUG: unable to handle page fault for address: ffff88824ca9b000
  Oops: Oops: 0000 [#1] SMP KASAN NOPTI
  RIP: 0010:netdev_nl_sock_priv_destroy+0xbd/0x1e0
  Call Trace:
   genl_release+0xf5/0x190
   netlink_release+0xd01/0x18d0
   __sock_release+0xb0/0x270
   sock_close+0x18/0x20

Add net_devmem_dev_unregister() called on NETDEV_UNREGISTER:
- When binding->dev (the physical DMA-capable device) unregisters,
  erase the binding ID, clear both binding->dev and binding->vdev, wait
  for in-flight RCU/TX readers via synchronize_net(), and unmap the
  dma_buf under binding->lock.
- When only binding->vdev (virtual device) unregisters while
  binding->dev lives, only clear binding->vdev so no new TX sends match
  the virtual device while allowing in-flight TX packets on binding->dev
  to finish DMA safely.

Fixes: bd61848900bf ("net: devmem: Implement TX path")
Fixes: 1abe839b34ae ("net: devmem: support TX over NETMEM_TX_NO_DMA devices")
Cc: Kaiyuan Zhang <kaiyuanz@google.com>
Cc: Stanislav Fomichev <sdf@fomichev.me>
Cc: Bobby Eshleman <bobbyeshleman@meta.com>
Cc: Tariq Toukan <tariqt@nvidia.com>
Cc: Kaifeng Wang <kaifengw@google.com>
Signed-off-by: Mina Almasry <almasrymina@google.com>
---
 net/core/devmem.c      | 45 ++++++++++++++++++++++++++++++++++++++++++
 net/core/devmem.h      |  5 +++++
 net/core/netdev-genl.c |  1 +
 3 files changed, 51 insertions(+)

diff --git a/net/core/devmem.c b/net/core/devmem.c
index 5e4070b82df44..da7b3e8abaa13 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c
@@ -169,6 +169,51 @@ void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding)
 	percpu_ref_kill(&binding->ref);
 }
 
+void net_devmem_dev_unregister(struct net_device *dev)
+{
+	struct net_devmem_dmabuf_binding *binding;
+	unsigned long xa_idx;
+
+	rcu_read_lock();
+	xa_for_each(&net_devmem_dmabuf_bindings, xa_idx, binding) {
+		if (!percpu_ref_tryget(&binding->ref))
+			continue;
+		rcu_read_unlock();
+
+		if (xa_empty(&binding->bound_rxqs)) {
+			if (READ_ONCE(binding->dev) == dev) {
+				xa_erase(&net_devmem_dmabuf_bindings,
+					 binding->id);
+
+				mutex_lock(&binding->lock);
+				WRITE_ONCE(binding->dev, NULL);
+				WRITE_ONCE(binding->vdev, NULL);
+				mutex_unlock(&binding->lock);
+
+				/* Ensure no tx net_devmem_lookup_dmabuf() or
+				 * validate_xmit_unreadable_skb() are in flight
+				 * after detach.
+				 */
+				synchronize_net();
+
+				mutex_lock(&binding->lock);
+				net_devmem_dmabuf_binding_unmap(binding);
+				mutex_unlock(&binding->lock);
+			} else if (READ_ONCE(binding->vdev) == dev) {
+				mutex_lock(&binding->lock);
+				WRITE_ONCE(binding->vdev, NULL);
+				mutex_unlock(&binding->lock);
+
+				synchronize_net();
+			}
+		}
+
+		net_devmem_dmabuf_binding_put(binding);
+		rcu_read_lock();
+	}
+	rcu_read_unlock();
+}
+
 int net_devmem_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx,
 				    struct net_devmem_dmabuf_binding *binding,
 				    struct netlink_ext_ack *extack)
diff --git a/net/core/devmem.h b/net/core/devmem.h
index 4a293a7d1149c..b572013d602c7 100644
--- a/net/core/devmem.h
+++ b/net/core/devmem.h
@@ -100,6 +100,7 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev,
 		       struct netlink_ext_ack *extack);
 struct net_devmem_dmabuf_binding *net_devmem_lookup_dmabuf(u32 id);
 void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding);
+void net_devmem_dev_unregister(struct net_device *dev);
 int net_devmem_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx,
 				    struct net_devmem_dmabuf_binding *binding,
 				    struct netlink_ext_ack *extack);
@@ -196,6 +197,10 @@ net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding)
 {
 }
 
+static inline void net_devmem_dev_unregister(struct net_device *dev)
+{
+}
+
 static inline int
 net_devmem_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx,
 				struct net_devmem_dmabuf_binding *binding,
diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
index 33b9f4eb9565a..5bfcd513fb0e8 100644
--- a/net/core/netdev-genl.c
+++ b/net/core/netdev-genl.c
@@ -1487,6 +1487,7 @@ static int netdev_genl_netdevice_event(struct notifier_block *nb,
 		netdev_unlock_full_to_ops(netdev);
 		break;
 	case NETDEV_UNREGISTER:
+		net_devmem_dev_unregister(netdev);
 		netdev_lock(netdev);
 		netdev_genl_dev_notify(netdev, NETDEV_CMD_DEV_DEL_NTF);
 		netdev_unlock(netdev);
-- 
2.56.0.385.gd3acb90ef8-goog

[PATCH net v1 3/4] netdevsim: support devmem RX and TX bindings

[Mina Almasry]

Set a 64-bit DMA mask on nsim_bus_dev, enable NETMEM_TX_DMA on the
netdevsim net_device, and configure page_pool instances with
PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV | PP_FLAG_ALLOW_UNREADABLE_NETMEM
and queue_idx so devmem bind-rx and bind-tx netlink operations can be
tested against netdevsim in software selftests.

Cc: Tariq Toukan <tariqt@nvidia.com>
Cc: Kaifeng Wang <kaifengw@google.com>
Signed-off-by: Mina Almasry <almasrymina@google.com>
---
 drivers/net/netdevsim/bus.c    |  1 +
 drivers/net/netdevsim/netdev.c | 21 +++++++++++++++------
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/net/netdevsim/bus.c b/drivers/net/netdevsim/bus.c
index 5c55c308487b4..f87f5e037b6fb 100644
--- a/drivers/net/netdevsim/bus.c
+++ b/drivers/net/netdevsim/bus.c
@@ -462,6 +462,7 @@ nsim_bus_dev_new(unsigned int id, unsigned int port_count, unsigned int num_queu
 	nsim_bus_dev->port_count = port_count;
 	nsim_bus_dev->num_queues = num_queues;
 	nsim_bus_dev->initial_net = current->nsproxy->net_ns;
+	dma_coerce_mask_and_coherent(&nsim_bus_dev->dev, DMA_BIT_MASK(64));
 	/* Disallow using nsim_bus_dev */
 	smp_store_release(&nsim_bus_dev->init, false);
 
diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index b4a99f3ceac60..4415dc01c610b 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -414,16 +414,22 @@ static int nsim_poll(struct napi_struct *napi, int budget)
 	return done;
 }
 
-static int nsim_create_page_pool(struct page_pool **p, struct napi_struct *napi)
+static int nsim_create_page_pool(struct net_device *dev, struct page_pool **p,
+				 struct napi_struct *napi, int idx)
 {
+	struct netdevsim *ns = netdev_priv(dev);
 	struct page_pool_params params = {
 		.order = 0,
 		.pool_size = NSIM_RING_SIZE,
+		.flags = PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV |
+			 PP_FLAG_ALLOW_UNREADABLE_NETMEM,
+		.max_len = PAGE_SIZE,
 		.nid = NUMA_NO_NODE,
-		.dev = &napi->dev->dev,
+		.dev = &ns->nsim_bus_dev->dev,
 		.napi = napi,
 		.dma_dir = DMA_BIDIRECTIONAL,
-		.netdev = napi->dev,
+		.netdev = dev,
+		.queue_idx = idx,
 	};
 	struct page_pool *pool;
 
@@ -450,7 +456,7 @@ static int nsim_init_napi(struct netdevsim *ns)
 	for (i = 0; i < dev->num_rx_queues; i++) {
 		rq = ns->rq[i];
 
-		err = nsim_create_page_pool(&rq->page_pool, &rq->napi);
+		err = nsim_create_page_pool(dev, &rq->page_pool, &rq->napi, i);
 		if (err)
 			goto err_pp_destroy;
 	}
@@ -762,14 +768,16 @@ nsim_queue_mem_alloc(struct net_device *dev,
 	if (ns->rq_reset_mode == 1) {
 		if (!netif_running(ns->netdev))
 			return -ENETDOWN;
-		return nsim_create_page_pool(&qmem->pp, &ns->rq[idx]->napi);
+		return nsim_create_page_pool(dev, &qmem->pp,
+					     &ns->rq[idx]->napi, idx);
 	}
 
 	qmem->rq = nsim_queue_alloc();
 	if (!qmem->rq)
 		return -ENOMEM;
 
-	err = nsim_create_page_pool(&qmem->rq->page_pool, &qmem->rq->napi);
+	err = nsim_create_page_pool(dev, &qmem->rq->page_pool, &qmem->rq->napi,
+				    idx);
 	if (err)
 		goto err_free;
 
@@ -1051,6 +1059,7 @@ static int nsim_init_netdevsim(struct netdevsim *ns)
 	ns->netdev->netdev_ops = &nsim_netdev_ops;
 	ns->netdev->stat_ops = &nsim_stat_ops;
 	ns->netdev->queue_mgmt_ops = &nsim_queue_mgmt_ops;
+	ns->netdev->netmem_tx = NETMEM_TX_DMA;
 	netdev_lockdep_set_classes(ns->netdev);
 
 	err = nsim_udp_tunnels_info_create(ns->nsim_dev, ns->netdev);
-- 
2.56.0.385.gd3acb90ef8-goog

[PATCH net v1 4/4] selftests: net: add devmem RX and TX netdev unregister tests

[Mina Almasry]

Add devmem_bind_rx_unregister_check and devmem_bind_tx_unregister_check
to nl_netdev.py to verify that unregistering a netdevsim device while a
netlink socket holds an active RX or TX devmem binding synchronously
detaches the dma_buf attachment and cleanly closes the netlink socket
without use-after-free or page faults.

Cc: Tariq Toukan <tariqt@nvidia.com>
Cc: Kaifeng Wang <kaifengw@google.com>
Signed-off-by: Mina Almasry <almasrymina@google.com>
---
 tools/testing/selftests/net/nl_netdev.py | 108 ++++++++++++++++++++++-
 1 file changed, 105 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/net/nl_netdev.py b/tools/testing/selftests/net/nl_netdev.py
index ceb44c8e1fec5..bad230ee9dcd2 100755
--- a/tools/testing/selftests/net/nl_netdev.py
+++ b/tools/testing/selftests/net/nl_netdev.py
@@ -6,10 +6,14 @@ Tests for the netdev netlink family.
 """
 
 import errno
+import fcntl
+import mmap
+import os
+import struct
 from os import system
-from lib.py import ksft_run, ksft_exit
+from lib.py import ksft_run, ksft_exit, KsftSkipEx
 from lib.py import ksft_eq, ksft_ge, ksft_ne, ksft_raises, ksft_busy_wait
-from lib.py import NetdevFamily, NetdevSimDev, NlError, defer, ip
+from lib.py import EthtoolFamily, NetdevFamily, NetdevSimDev, NlError, defer, ip
 
 
 def empty_check(nf) -> None:
@@ -366,6 +370,102 @@ def page_pool_stats_ifindex_check(nf) -> None:
     ksft_eq(cm.exception.nl_msg.extack['bad-attr'], '.info.id')
 
 
+def _create_udmabuf(num_pages=64) -> int:
+    """Create a sealed memfd-backed udmabuf fd for devmem tests."""
+    if not os.path.exists("/dev/udmabuf"):
+        raise KsftSkipEx("/dev/udmabuf is not available")
+
+    size = num_pages * mmap.PAGESIZE
+    memfd = os.memfd_create("devmem-ksft", os.MFD_ALLOW_SEALING)
+    os.ftruncate(memfd, size)
+    fcntl.fcntl(memfd, 1033, 0x0002)  # F_ADD_SEALS, F_SEAL_SHRINK
+    devfd = os.open("/dev/udmabuf", os.O_RDWR)
+    req = bytearray(struct.pack("IIQQ", memfd, 0, 0, size))
+    dmabuf_fd = fcntl.ioctl(devfd, 0x40187542, req)  # UDMABUF_CREATE
+    os.close(devfd)
+    os.close(memfd)
+    return dmabuf_fd
+
+
+def _dmabuf_attached_devs():
+    """Return attached device names from debugfs dma_buf/bufinfo if available."""
+    path = "/sys/kernel/debug/dma_buf/bufinfo"
+    if not os.path.exists(path):
+        return None
+    with open(path, "r", encoding="utf-8") as f:
+        text = f.read()
+    attached = []
+    in_attached = False
+    for line in text.splitlines():
+        if line.strip() == "Attached Devices:":
+            in_attached = True
+            continue
+        if in_attached:
+            if line.startswith("\t") and line.strip():
+                attached.append(line.strip())
+            else:
+                in_attached = False
+    return attached
+
+
+def devmem_bind_rx_unregister_check(_nf) -> None:
+    """Verify RX devmem bindings detach dma_buf synchronously on netdev unregister."""
+    dmabuf_fd = _create_udmabuf()
+    nf_priv = NetdevFamily()
+    ef = EthtoolFamily()
+    nsimdev = NetdevSimDev(queue_count=2)
+    nsim = nsimdev.nsims[0]
+
+    ip(f"link set dev {nsim.ifname} up")
+    ef.rings_set({"header": {"dev-index": nsim.ifindex},
+                  "tcp-data-split": "enabled"})
+    nf_priv.bind_rx({
+        "ifindex": nsim.ifindex,
+        "fd": dmabuf_fd,
+        "queues": [{"id": 1, "type": "rx"}],
+    })
+
+    attached = _dmabuf_attached_devs()
+    if attached is not None:
+        ksft_ge(len(attached), 1)
+
+    nsimdev.remove()
+
+    attached = _dmabuf_attached_devs()
+    if attached is not None:
+        ksft_eq(len(attached), 0)
+
+    del nf_priv
+    os.close(dmabuf_fd)
+
+
+def devmem_bind_tx_unregister_check(_nf) -> None:
+    """Verify TX devmem bindings detach cleanly on netdev unregister without UAF."""
+    dmabuf_fd = _create_udmabuf()
+    nf_priv = NetdevFamily()
+    nsimdev = NetdevSimDev(queue_count=2)
+    nsim = nsimdev.nsims[0]
+
+    ip(f"link set dev {nsim.ifname} up")
+    nf_priv.bind_tx({
+        "ifindex": nsim.ifindex,
+        "fd": dmabuf_fd,
+    })
+
+    attached = _dmabuf_attached_devs()
+    if attached is not None:
+        ksft_ge(len(attached), 1)
+
+    nsimdev.remove()
+
+    attached = _dmabuf_attached_devs()
+    if attached is not None:
+        ksft_eq(len(attached), 0)
+
+    del nf_priv
+    os.close(dmabuf_fd)
+
+
 def main() -> None:
     """ Ksft boiler plate main """
     nf = NetdevFamily()
@@ -379,7 +479,9 @@ def main() -> None:
               page_pool_check,
               page_pool_dump_ifindex,
               page_pool_ifindex_leak_check,
-              page_pool_stats_ifindex_check
+              page_pool_stats_ifindex_check,
+              devmem_bind_rx_unregister_check,
+              devmem_bind_tx_unregister_check
               ],
              args=(nf, ))
     ksft_exit()
-- 
2.56.0.385.gd3acb90ef8-goog

Re: [PATCH net v1 1/4] net: devmem: unmap dma_buf synchronously on queue uninstall

[Pavel Begunkov]

On 10/10/26 03:55, Mina Almasry wrote:
> When a bound net_device is unregistered while userspace still holds a
> netlink or TCP socket reference on a devmem binding,
> mp_dmabuf_devmem_uninstall() clears binding->dev to NULL so
> netdev_nl_sock_priv_destroy() will not touch the unregistered
> net_device, but leaves the dma_buf attachment mapped until
> __net_devmem_dmabuf_binding_free() runs later on socket close.
> 
> Because dma_buf_attach() does not take a reference on dma_dev, device
> removal frees dma_dev while the attachment is still mapped. Closing the
> netlink socket afterwards triggers a slab use-after-free in
> dma_unmap_sg_attrs():
> 
>    BUG: KASAN: slab-use-after-free in dma_unmap_sg_attrs+0x76/0x2b0
>    Read of size 8 at addr ffff88810fae64b0 by task kworker/3:1/53
>    Workqueue: events __net_devmem_dmabuf_binding_free
>    Call Trace:
>     dma_unmap_sg_attrs+0x76/0x2b0
>     unmap_udmabuf+0x8e/0x100
>     dma_buf_unmap_attachment+0x145/0x330
>     dma_buf_unmap_attachment_unlocked+0x96/0x130
>     __net_devmem_dmabuf_binding_free+0x156/0x2e0
>    Freed by task 9:
>     kfree+0x1b8/0x550
>     nsim_bus_dev_release+0xe/0x60
>     device_release+0xcf/0x250
> 
> Add net_devmem_dmabuf_binding_unmap() serialized under binding->lock
> and null out binding->sgt and binding->attachment after unmapping so
> unmapping is idempotent across queue uninstall and deferred binding
> destruction. Call it synchronously when the last bound RX queue is
> uninstalled in mp_dmabuf_devmem_uninstall().
> 
> Fixes: f8350a4358fc ("net: page_pool: add a mp hook to unregister_netdevice*")

It looks more like 170aafe35cb98e0f3fbacb446ea86389fbce22ea
("netdev: support binding dma-buf to netdevice"). The one in the
tag didn't do anything interesting.

The fix looks good as well, might be a good idea to clear
net_iov's dma_addr as well.

Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>

-- 
Pavel Begunkov