The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to [off-list ref].

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From c7d9be66b71af490446127c6ffcb66d6bb71b8b9 Mon Sep 17 00:00:00 2001
From: Ethan Nelson-Moore <redacted>
Date: Thu, 12 Feb 2026 20:55:09 -0800
Subject: [PATCH] net: arcnet: com20020-pci: fix support for 2.5Mbit cards

Commit 8c14f9c70327 ("ARCNET: add com20020 PCI IDs with metadata")
converted the com20020-pci driver to use a card info structure instead
of a single flag mask in driver_data. However, it failed to take into
account that in the original code, driver_data of 0 indicates a card
with no special flags, not a card that should not have any card info
structure. This introduced a null pointer dereference when cards with
no flags were probed.

Commit bd6f1fd5d33d ("net: arcnet: com20020: Fix null-ptr-deref in
com20020pci_probe()") then papered over this issue by rejecting cards
with no driver_data instead of resolving the problem at its source.

Fix the original issue by introducing a new card info structure for
2.5Mbit cards that does not set any flags and using it if no
driver_data is present.

Fixes: 8c14f9c70327 ("ARCNET: add com20020 PCI IDs with metadata")
Fixes: bd6f1fd5d33d ("net: arcnet: com20020: Fix null-ptr-deref in com20020pci_probe()")
Cc: stable@vger.kernel.org
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Ethan Nelson-Moore <redacted>
Link: https://patch.msgid.link/20260213045510.32368-1-enelsonmoore@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 drivers/net/arcnet/com20020-pci.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/net/arcnet/com20020-pci.c b/drivers/net/arcnet/com20020-pci.c
index 19e411b2e3a77..dbadda08dce23 100644
--- a/drivers/net/arcnet/com20020-pci.c
+++ b/drivers/net/arcnet/com20020-pci.c

@@ -115,6 +115,8 @@ static const struct attribute_group com20020_state_group = {
 	.attrs = com20020_state_attrs,
 };
 
+static struct com20020_pci_card_info card_info_2p5mbit;
+
 static void com20020pci_remove(struct pci_dev *pdev);
 
 static int com20020pci_probe(struct pci_dev *pdev,

@@ -140,7 +142,7 @@ static int com20020pci_probe(struct pci_dev *pdev,
 
 	ci = (struct com20020_pci_card_info *)id->driver_data;
 	if (!ci)
-		return -EINVAL;
+		ci = &card_info_2p5mbit;
 
 	priv->ci = ci;
 	mm = &ci->misc_map;

@@ -347,6 +349,18 @@ static struct com20020_pci_card_info card_info_5mbit = {
 	.flags = ARC_IS_5MBIT,
 };
 
+static struct com20020_pci_card_info card_info_2p5mbit = {
+	.name = "ARC-PCI",
+	.devcount = 1,
+	.chan_map_tbl = {
+		{
+			.bar = 2,
+			.offset = 0x00,
+			.size = 0x08,
+		},
+	},
+};
+
 static struct com20020_pci_card_info card_info_sohard = {
 	.name = "SOHARD SH ARC-PCI",
 	.devcount = 1,

-- 
2.51.0