[PATCH net] netdev: avoid CFI problems with sock priv helpers

[Jakub Kicinski <kuba@kernel.org>]

Li Li reports that casting away callback type may cause issues
for CFI. Let's generate a small wrapper for each callback,
to make sure compiler sees the anticipated types.

Reported-by: Li Li <dualli@chromium.org>
Link: https://lore.kernel.org/CANBPYPjQVqmzZ4J=rVQX87a9iuwmaetULwbK_5_3YWk2eGzkaA@mail.gmail.com
Fixes: 170aafe35cb9 ("netdev: support binding dma-buf to netdevice")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: donald.hunter@gmail.com
CC: sdf@fomichev.me
CC: almasrymina@google.com
---
 net/core/netdev-genl-gen.c | 14 ++++++++++++--
 tools/net/ynl/ynl-gen-c.py | 16 +++++++++++++---
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/net/core/netdev-genl-gen.c b/net/core/netdev-genl-gen.c
index a89cbd8d87c3..996ac6a449eb 100644
--- a/net/core/netdev-genl-gen.c
+++ b/net/core/netdev-genl-gen.c
@@ -197,6 +197,16 @@ static const struct genl_multicast_group netdev_nl_mcgrps[] = {
 	[NETDEV_NLGRP_PAGE_POOL] = { "page-pool", },
 };
 
+static void __netdev_nl_sock_priv_init(void *priv)
+{
+	netdev_nl_sock_priv_init(priv);
+}
+
+static void __netdev_nl_sock_priv_destroy(void *priv)
+{
+	netdev_nl_sock_priv_destroy(priv);
+}
+
 struct genl_family netdev_nl_family __ro_after_init = {
 	.name		= NETDEV_FAMILY_NAME,
 	.version	= NETDEV_FAMILY_VERSION,
@@ -208,6 +218,6 @@ struct genl_family netdev_nl_family __ro_after_init = {
 	.mcgrps		= netdev_nl_mcgrps,
 	.n_mcgrps	= ARRAY_SIZE(netdev_nl_mcgrps),
 	.sock_priv_size	= sizeof(struct list_head),
-	.sock_priv_init	= (void *)netdev_nl_sock_priv_init,
-	.sock_priv_destroy = (void *)netdev_nl_sock_priv_destroy,
+	.sock_priv_init	= __netdev_nl_sock_priv_init,
+	.sock_priv_destroy = __netdev_nl_sock_priv_destroy,
 };
diff --git a/tools/net/ynl/ynl-gen-c.py b/tools/net/ynl/ynl-gen-c.py
index d8201c4b1520..6750fdb42564 100755
--- a/tools/net/ynl/ynl-gen-c.py
+++ b/tools/net/ynl/ynl-gen-c.py
@@ -2384,6 +2384,17 @@ _C_KW = {
     if not kernel_can_gen_family_struct(family):
         return
 
+    if 'sock-priv' in family.kernel_family:
+        # Generate "trampolines" to make CFI happy
+        cw.write_func("static void", f"__{family.c_name}_nl_sock_priv_init",
+                      [f"{family.c_name}_nl_sock_priv_init(priv);"],
+                      ["void *priv"])
+        cw.nl()
+        cw.write_func("static void", f"__{family.c_name}_nl_sock_priv_destroy",
+                      [f"{family.c_name}_nl_sock_priv_destroy(priv);"],
+                      ["void *priv"])
+        cw.nl()
+
     cw.block_start(f"struct genl_family {family.ident_name}_nl_family __ro_after_init =")
     cw.p('.name\t\t= ' + family.fam_key + ',')
     cw.p('.version\t= ' + family.ver_key + ',')
@@ -2401,9 +2412,8 @@ _C_KW = {
         cw.p(f'.n_mcgrps\t= ARRAY_SIZE({family.c_name}_nl_mcgrps),')
     if 'sock-priv' in family.kernel_family:
         cw.p(f'.sock_priv_size\t= sizeof({family.kernel_family["sock-priv"]}),')
-        # Force cast here, actual helpers take pointer to the real type.
-        cw.p(f'.sock_priv_init\t= (void *){family.c_name}_nl_sock_priv_init,')
-        cw.p(f'.sock_priv_destroy = (void *){family.c_name}_nl_sock_priv_destroy,')
+        cw.p(f'.sock_priv_init\t= __{family.c_name}_nl_sock_priv_init,')
+        cw.p(f'.sock_priv_destroy = __{family.c_name}_nl_sock_priv_destroy,')
     cw.block_end(';')
 
 
-- 
2.48.0