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netdev: avoid CFI problems with sock priv helpers

PATCH Applied Jakub Kicinski 4 participants 4 messages Jan 15, 2025 – Jan 16, 2025

Subsystems (3)
Networking Network drivers YAML netlink (YNL)
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Jakub Kicinski

author maintainer
#0 lore raw

PATCH 1/1 netdev: avoid CFI problems with sock priv helpers

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 <[email protected]>
Link https://lore.kernel.org/CANBPYPjQVqmzZ4J=rVQX87a9iuwmaetULwbK_5_3YWk2eGzkaA@mail.gmail.com open here
Fixes 170aafe35cb9 ("netdev: support binding dma-buf to netdevice")
Signed-off-by Jakub Kicinski <[email protected]>

---
CC: [email protected]
CC: [email protected]
CC: [email protected]

---
 net/core/netdev-genl-gen.c | 14 ++++++++++++--
 tools/net/ynl/ynl-gen-c.py | 16 +++++++++++++---
 2 files changed, 25 insertions(+), 5 deletions(-)
net/core/netdev-genl-gen.c +12 -2
index a89cbd8d87c3..996ac6a449eb 100644
@@ -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,
 };
tools/net/ynl/ynl-gen-c.py +13 -3
index d8201c4b1520..6750fdb42564 100755
@@ -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(';')
Signature · 1 line
2.48.0
Reviewed-by on v1 1/1
#1 lore raw
Quoted 9 lines · Jakub Kicinski

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 <[email protected]>
Link https://lore.kernel.org/CANBPYPjQVqmzZ4J=rVQX87a9iuwmaetULwbK_5_3YWk2eGzkaA@mail.gmail.com open here
Fixes 170aafe35cb9 ("netdev: support binding dma-buf to netdevice")
Signed-off-by Jakub Kicinski <[email protected]>

Thanks Jakub,

Reviewed-by Mina Almasry <[email protected]>
CI Applied
#2 lore raw
In reply to Jakub Kicinski
This patch was applied to netdev/net.git (main) by Paolo Abeni <[email protected]>:

Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <[email protected]>:

Quoted 10 lines · On Wed, 15 Jan 2025 08:14:36 -0800 you wrote:

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 <[email protected]>
Link https://lore.kernel.org/CANBPYPjQVqmzZ4J=rVQX87a9iuwmaetULwbK_5_3YWk2eGzkaA@mail.gmail.com open here
Fixes 170aafe35cb9 ("netdev: support binding dma-buf to netdevice")
Signed-off-by Jakub Kicinski <[email protected]>

[...]

Here is the summary with links:
- [net] netdev: avoid CFI problems with sock priv helpers

    https://git.kernel.org/netdev/net/c/a50da36562cd

You are awesome, thank you!

Signature · 2 lines
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maintainer
#3 lore raw
In reply to Jakub Kicinski
Quoted 4 lines · Jakub Kicinski

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.

Quoted 8 lines
Reported-by Li Li <[email protected]>
Link https://lore.kernel.org/CANBPYPjQVqmzZ4J=rVQX87a9iuwmaetULwbK_5_3YWk2eGzkaA@mail.gmail.com open here
Fixes 170aafe35cb9 ("netdev: support binding dma-buf to netdevice")
Signed-off-by Jakub Kicinski <[email protected]>

---
CC: [email protected]
CC: [email protected]
CC: [email protected]

FTR, I took the liberty of applying this patch before the 24H grace period to fit todays net PR and avoid shipping a 6.13 final with a known serious issue.

/P