x86/amd_node: Fix PCI device reference counting in amd_smn_init()grafted

The local "root" pointer is a temporary variable used during the device
search. Therefore, refcount related to the search iterators should be cleaned
up after the search is complete.

Use the __free() cleanup macro to ensure the refcount is decremented when the
temporary pointer goes out of scope.

Additionally, increment the refcount when caching a root pointer. This ensures
the in-use refcount is separate from the temporary search refcounting.

Finally, drop the redundant "root = NULL" before the second search loop. The
pci_get_class() iterator always decrements the refcount of its "from"
argument, so the first loop can only fall through with "root" already NULL.

Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching")
Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com
Reported-by: Sashiko <sashiko-bot@kernel.org>
Assisted-by: LLM
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Cc: <stable@kernel.org>
Link: https://patch.msgid.link/20260903154325.74343-1-yazen.ghannam@amd.com

1 files changed, 72 insertions, 0 deletions

diff --git a/net/ipv4/fib_notifier.c b/net/ipv4/fib_notifier.c
new file mode 100644
index 000000000..b1551c265
--- /dev/null
+++ b/net/ipv4/fib_notifier.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/rtnetlink.h>
+#include <linux/notifier.h>
+#include <linux/socket.h>
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <net/net_namespace.h>
+#include <net/fib_notifier.h>
+#include <net/ip_fib.h>
+
+int call_fib4_notifier(struct notifier_block *nb,
+		       enum fib_event_type event_type,
+		       struct fib_notifier_info *info)
+{
+	info->family = AF_INET;
+	return call_fib_notifier(nb, event_type, info);
+}
+
+int call_fib4_notifiers(struct net *net, enum fib_event_type event_type,
+			struct fib_notifier_info *info)
+{
+	ASSERT_RTNL();
+
+	info->family = AF_INET;
+	/* Paired with READ_ONCE() in fib4_seq_read() */
+	WRITE_ONCE(net->ipv4.fib_seq, net->ipv4.fib_seq + 1);
+	return call_fib_notifiers(net, event_type, info);
+}
+
+static unsigned int fib4_seq_read(const struct net *net)
+{
+	/* Paired with WRITE_ONCE() in call_fib4_notifiers() */
+	return READ_ONCE(net->ipv4.fib_seq) + fib4_rules_seq_read(net);
+}
+
+static int fib4_dump(struct net *net, struct notifier_block *nb,
+		     struct netlink_ext_ack *extack)
+{
+	int err;
+
+	err = fib4_rules_dump(net, nb, extack);
+	if (err)
+		return err;
+
+	return fib_notify(net, nb, extack);
+}
+
+static const struct fib_notifier_ops fib4_notifier_ops_template = {
+	.family		= AF_INET,
+	.fib_seq_read	= fib4_seq_read,
+	.fib_dump	= fib4_dump,
+	.owner		= THIS_MODULE,
+};
+
+int __net_init fib4_notifier_init(struct net *net)
+{
+	struct fib_notifier_ops *ops;
+
+	net->ipv4.fib_seq = 0;
+
+	ops = fib_notifier_ops_register(&fib4_notifier_ops_template, net);
+	if (IS_ERR(ops))
+		return PTR_ERR(ops);
+	net->ipv4.notifier_ops = ops;
+
+	return 0;
+}
+
+void __net_exit fib4_notifier_exit(struct net *net)
+{
+	fib_notifier_ops_unregister(net->ipv4.notifier_ops);
+}