Backport fix for crash on netvm change

Fixes QubesOS/qubes-issues#7257
marmarek · Feb 26, 2022 · 78a27fc · 78a27fc
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diff --git a/0001-xen-netfront-destroy-queues-before-real_num_tx_queue.patch b/0001-xen-netfront-destroy-queues-before-real_num_tx_queue.patch
@@ -0,0 +1,136 @@
+From dcf4ff7a48e7598e6b10126cc02177abb8ae4f3f Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Marek=20Marczykowski-G=C3=B3recki?=
+ <marmarek@invisiblethingslab.com>
+Date: Wed, 23 Feb 2022 22:19:54 +0100
+Subject: [PATCH] xen/netfront: destroy queues before real_num_tx_queues is
+ zeroed
+
+xennet_destroy_queues() relies on info->netdev->real_num_tx_queues to
+delete queues. Since d7dac083414eb5bb99a6d2ed53dc2c1b405224e5
+("net-sysfs: update the queue counts in the unregistration path"),
+unregister_netdev() indirectly sets real_num_tx_queues to 0. Those two
+facts together means, that xennet_destroy_queues() called from
+xennet_remove() cannot do its job, because it's called after
+unregister_netdev(). This results in kfree-ing queues that are still
+linked in napi, which ultimately crashes:
+
+    BUG: kernel NULL pointer dereference, address: 0000000000000000
+    #PF: supervisor read access in kernel mode
+    #PF: error_code(0x0000) - not-present page
+    PGD 0 P4D 0
+    Oops: 0000 [#1] PREEMPT SMP PTI
+    CPU: 1 PID: 52 Comm: xenwatch Tainted: G        W         5.16.10-1.32.fc32.qubes.x86_64+ #226
+    RIP: 0010:free_netdev+0xa3/0x1a0
+    Code: ff 48 89 df e8 2e e9 00 00 48 8b 43 50 48 8b 08 48 8d b8 a0 fe ff ff 48 8d a9 a0 fe ff ff 49 39 c4 75 26 eb 47 e8 ed c1 66 ff <48> 8b 85 60 01 00 00 48 8d 95 60 01 00 00 48 89 ef 48 2d 60 01 00
+    RSP: 0000:ffffc90000bcfd00 EFLAGS: 00010286
+    RAX: 0000000000000000 RBX: ffff88800edad000 RCX: 0000000000000000
+    RDX: 0000000000000001 RSI: ffffc90000bcfc30 RDI: 00000000ffffffff
+    RBP: fffffffffffffea0 R08: 0000000000000000 R09: 0000000000000000
+    R10: 0000000000000000 R11: 0000000000000001 R12: ffff88800edad050
+    R13: ffff8880065f8f88 R14: 0000000000000000 R15: ffff8880066c6680
+    FS:  0000000000000000(0000) GS:ffff8880f3300000(0000) knlGS:0000000000000000
+    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
+    CR2: 0000000000000000 CR3: 00000000e998c006 CR4: 00000000003706e0
+    Call Trace:
+     <TASK>
+     xennet_remove+0x13d/0x300 [xen_netfront]
+     xenbus_dev_remove+0x6d/0xf0
+     __device_release_driver+0x17a/0x240
+     device_release_driver+0x24/0x30
+     bus_remove_device+0xd8/0x140
+     device_del+0x18b/0x410
+     ? _raw_spin_unlock+0x16/0x30
+     ? klist_iter_exit+0x14/0x20
+     ? xenbus_dev_request_and_reply+0x80/0x80
+     device_unregister+0x13/0x60
+     xenbus_dev_changed+0x18e/0x1f0
+     xenwatch_thread+0xc0/0x1a0
+     ? do_wait_intr_irq+0xa0/0xa0
+     kthread+0x16b/0x190
+     ? set_kthread_struct+0x40/0x40
+     ret_from_fork+0x22/0x30
+     </TASK>
+
+Fix this by calling xennet_destroy_queues() from xennet_uninit(),
+when real_num_tx_queues is still available. This ensures that queues are
+destroyed when real_num_tx_queues is set to 0, regardless of how
+unregister_netdev() was called.
+
+Originally reported at
+https://github.com/QubesOS/qubes-issues/issues/7257
+
+Fixes: d7dac083414eb5bb9 ("net-sysfs: update the queue counts in the unregistration path")
+Cc: stable@vger.kernel.org
+Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ drivers/net/xen-netfront.c | 39 ++++++++++++++++++++++----------------
+ 1 file changed, 23 insertions(+), 16 deletions(-)
+
+diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
+index 8b18246ad999..7748f07e2cf1 100644
+--- a/drivers/net/xen-netfront.c
++++ b/drivers/net/xen-netfront.c
+@@ -842,6 +842,28 @@ static int xennet_close(struct net_device *dev)
+ 	return 0;
+ }
+
++static void xennet_destroy_queues(struct netfront_info *info)
++{
++	unsigned int i;
++
++	for (i = 0; i < info->netdev->real_num_tx_queues; i++) {
++		struct netfront_queue *queue = &info->queues[i];
++
++		if (netif_running(info->netdev))
++			napi_disable(&queue->napi);
++		netif_napi_del(&queue->napi);
++	}
++
++	kfree(info->queues);
++	info->queues = NULL;
++}
++
++static void xennet_uninit(struct net_device *dev)
++{
++	struct netfront_info *np = netdev_priv(dev);
++	xennet_destroy_queues(np);
++}
++
+ static void xennet_set_rx_rsp_cons(struct netfront_queue *queue, RING_IDX val)
+ {
+ 	unsigned long flags;
+@@ -1611,6 +1633,7 @@ static int xennet_xdp(struct net_device *dev, struct netdev_bpf *xdp)
+ }
+
+ static const struct net_device_ops xennet_netdev_ops = {
++	.ndo_uninit          = xennet_uninit,
+ 	.ndo_open            = xennet_open,
+ 	.ndo_stop            = xennet_close,
+ 	.ndo_start_xmit      = xennet_start_xmit,
+@@ -2103,22 +2126,6 @@ static int write_queue_xenstore_keys(struct netfront_queue *queue,
+ 	return err;
+ }
+
+-static void xennet_destroy_queues(struct netfront_info *info)
+-{
+-	unsigned int i;
+-
+-	for (i = 0; i < info->netdev->real_num_tx_queues; i++) {
+-		struct netfront_queue *queue = &info->queues[i];
+-
+-		if (netif_running(info->netdev))
+-			napi_disable(&queue->napi);
+-		netif_napi_del(&queue->napi);
+-	}
+-
+-	kfree(info->queues);
+-	info->queues = NULL;
+-}
+-
+
+
+ static int xennet_create_page_pool(struct netfront_queue *queue)
+-- 
+2.31.1
+
diff --git a/kernel.spec.in b/kernel.spec.in
@@ -134,6 +134,7 @@ Patch12: 0013-xen-pcifront-pciback-Update-pciif.h-with-err-and-res.patch
 Patch14: 0001-Revert-xen-netback-Check-for-hotplug-status-existenc.patch
 Patch15: 0002-Revert-xen-netback-remove-hotplug-status-once-it-has.patch
 Patch16: 0001-usbip-tweak-clear-halt-with-simple-reset.patch
+Patch17: 0001-xen-netfront-destroy-queues-before-real_num_tx_queue.patch
 
 %description
 Qubes Dom0 kernel.