fix: patch Linux with blackhole patch

See siderolabs/talos#9837 This causes invalid Ethernet packets to be sent out, which might trigger unrelated issues in some environments. See: * git.kernel.org/netdev/net/c/0e4427f8f587 * lore.kernel.org/netdev/[email protected]/T Signed-off-by: Andrey Smirnov <[email protected]>
smira · Feb 25, 2025 · cc5317a · cc5317a
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commit cc5317a
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diff --git a/kernel/build/patches/README.md b/kernel/build/patches/README.md
@@ -1,3 +1,3 @@
 | Patch file                                                                 | Description                                | Upstream status | Link                                                                                                                                                                                                         |
 |----------------------------------------------------------------------------|--------------------------------------------|-----------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
-| mpt3sas-ubsan.patch | Backport fixes for UBSAN reporting | in 6.8 | Commit fd7090e384725edb1910a4b0a9c51007858f2c81 |
+| blackhole.patch | Backport fixes for blackhole device sending packets without Ethernet header | in 6.14 | Commit 	0e4427f8f587c4b603475468bb3aee9418574893 |
diff --git a/kernel/build/patches/blackhole.patch b/kernel/build/patches/blackhole.patch
@@ -0,0 +1,89 @@
+From 0e4427f8f587c4b603475468bb3aee9418574893 Mon Sep 17 00:00:00 2001
+From: Ido Schimmel <[email protected]>
+Date: Thu, 20 Feb 2025 09:25:59 +0200
+Subject: net: loopback: Avoid sending IP packets without an Ethernet header
+
+After commit 22600596b675 ("ipv4: give an IPv4 dev to blackhole_netdev")
+IPv4 neighbors can be constructed on the blackhole net device, but they
+are constructed with an output function (neigh_direct_output()) that
+simply calls dev_queue_xmit(). The latter will transmit packets via
+'skb->dev' which might not be the blackhole net device if dst_dev_put()
+switched 'dst->dev' to the blackhole net device while another CPU was
+using the dst entry in ip_output(), but after it already initialized
+'skb->dev' from 'dst->dev'.
+
+Specifically, the following can happen:
+
+    CPU1                                      CPU2
+
+udp_sendmsg(sk1)                          udp_sendmsg(sk2)
+udp_send_skb()                            [...]
+ip_output()
+    skb->dev = skb_dst(skb)->dev
+                                          dst_dev_put()
+                                              dst->dev = blackhole_netdev
+ip_finish_output2()
+    resolves neigh on dst->dev
+neigh_output()
+neigh_direct_output()
+dev_queue_xmit()
+
+This will result in IPv4 packets being sent without an Ethernet header
+via a valid net device:
+
+tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
+listening on enp9s0, link-type EN10MB (Ethernet), snapshot length 262144 bytes
+22:07:02.329668 20:00:40:11:18:fb > 45:00:00:44:f4:94, ethertype Unknown
+(0x58c6), length 68:
+        0x0000:  8dda 74ca f1ae ca6c ca6c 0098 969c 0400  ..t....l.l......
+        0x0010:  0000 4730 3f18 6800 0000 0000 0000 9971  ..G0?.h........q
+        0x0020:  c4c9 9055 a157 0a70 9ead bf83 38ca ab38  ...U.W.p....8..8
+        0x0030:  8add ab96 e052                           .....R
+
+Fix by making sure that neighbors are constructed on top of the
+blackhole net device with an output function that simply consumes the
+packets, in a similar fashion to dst_discard_out() and
+blackhole_netdev_xmit().
+
+Fixes: 8d7017fd621d ("blackhole_netdev: use blackhole_netdev to invalidate dst entries")
+Fixes: 22600596b675 ("ipv4: give an IPv4 dev to blackhole_netdev")
+Reported-by: Florian Meister <[email protected]>
+Closes: https://lore.kernel.org/netdev/[email protected]/
+Signed-off-by: Ido Schimmel <[email protected]>
+Reviewed-by: Eric Dumazet <[email protected]>
+Link: https://patch.msgid.link/[email protected]
+Signed-off-by: Jakub Kicinski <[email protected]>
+---
+ drivers/net/loopback.c | 14 ++++++++++++++
+ 1 file changed, 14 insertions(+)
+
+diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
+index c8840c3b9a1bc7..f1d68153987e1b 100644
+--- a/drivers/net/loopback.c
++++ b/drivers/net/loopback.c
+@@ -244,8 +244,22 @@ static netdev_tx_t blackhole_netdev_xmit(struct sk_buff *skb,
+ 	return NETDEV_TX_OK;
+ }
+
++static int blackhole_neigh_output(struct neighbour *n, struct sk_buff *skb)
++{
++	kfree_skb(skb);
++	return 0;
++}
++
++static int blackhole_neigh_construct(struct net_device *dev,
++				     struct neighbour *n)
++{
++	n->output = blackhole_neigh_output;
++	return 0;
++}
++
+ static const struct net_device_ops blackhole_netdev_ops = {
+ 	.ndo_start_xmit = blackhole_netdev_xmit,
++	.ndo_neigh_construct = blackhole_neigh_construct,
+ };
+
+ /* This is a dst-dummy device used specifically for invalidated
+-- 
+cgit 1.2.3-korg
+
diff --git a/kernel/build/pkg.yaml b/kernel/build/pkg.yaml
@@ -16,6 +16,7 @@ steps:
         cd /src
         for patch in $(find /pkg/patches -type f -name "*.patch" | sort); do
           patch -p1 < $patch || (echo "Failed to apply patch $patch" && exit 1)
+          echo "Applied patch $patch"
         done
     build:
       {{ if .BUILD_ARG_KERNEL_TARGET }}