From: Nathan Chancellor <nathan@kernel.org>

Date: Thu, 3 Nov 2022 10:01:28 -0700

Subject: s390/ctcm: Fix return type of ctc{mp,}m_tx()

Git-commit: aa5bf80c3c067b82b4362cd6e8e2194623bcaca6

Patch-mainline: v6.2-rc1

References: git-fixes bsc#1211686

With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG),

indirect call targets are validated against the expected function

pointer prototype to make sure the call target is valid to help mitigate

ROP attacks. If they are not identical, there is a failure at run time,

which manifests as either a kernel panic or thread getting killed. A

proposed warning in clang aims to catch these at compile time, which

reveals:

  drivers/s390/net/ctcm_main.c:1064:21: error: incompatible function pointer types initializing 'netdev_tx_t (*)(struct sk_buff *, struct net_device *)' (aka 'enum netdev_tx (*)(struct sk_buff *, struct net_device *)') with an expression of type 'int (struct sk_buff *, struct net_device *)' [-Werror,-Wincompatible-function-pointer-types-strict]

          .ndo_start_xmit         = ctcm_tx,

                                    ^~~~~~~

  drivers/s390/net/ctcm_main.c:1072:21: error: incompatible function pointer types initializing 'netdev_tx_t (*)(struct sk_buff *, struct net_device *)' (aka 'enum netdev_tx (*)(struct sk_buff *, struct net_device *)') with an expression of type 'int (struct sk_buff *, struct net_device *)' [-Werror,-Wincompatible-function-pointer-types-strict]

          .ndo_start_xmit         = ctcmpc_tx,

                                    ^~~~~~~~~

->ndo_start_xmit() in 'struct net_device_ops' expects a return type of

'netdev_tx_t', not 'int'. Adjust the return type of ctc{mp,}m_tx() to

match the prototype's to resolve the warning and potential CFI failure,

should s390 select ARCH_SUPPORTS_CFI_CLANG in the future.

Additionally, while in the area, remove a comment block that is no

longer relevant.

Link: https://github.com/ClangBuiltLinux/linux/issues/1750

Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Signed-off-by: David S. Miller <davem@davemloft.net>

Acked-by: Miroslav Franc <mfranc@suse.cz>

---

 drivers/s390/net/ctcm_main.c | 11 ++---------

 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/drivers/s390/net/ctcm_main.c b/drivers/s390/net/ctcm_main.c

index 37b551bd43bf..bdfab9ea0046 100644

--- a/drivers/s390/net/ctcm_main.c

+++ b/drivers/s390/net/ctcm_main.c

@@ -825,16 +825,9 @@ static int ctcmpc_transmit_skb(struct channel *ch, struct sk_buff *skb)

 /**

  * Start transmission of a packet.

  * Called from generic network device layer.

- *

- *  skb		Pointer to buffer containing the packet.

- *  dev		Pointer to interface struct.

- *

- * returns 0 if packet consumed, !0 if packet rejected.

- *         Note: If we return !0, then the packet is free'd by

- *               the generic network layer.

  */

 /* first merge version - leaving both functions separated */

-static int ctcm_tx(struct sk_buff *skb, struct net_device *dev)

+static netdev_tx_t ctcm_tx(struct sk_buff *skb, struct net_device *dev)

 {

 	struct ctcm_priv *priv = dev->ml_priv;

@@ -877,7 +870,7 @@ static int ctcm_tx(struct sk_buff *skb, struct net_device *dev)

 }

 /* unmerged MPC variant of ctcm_tx */

-static int ctcmpc_tx(struct sk_buff *skb, struct net_device *dev)

+static netdev_tx_t ctcmpc_tx(struct sk_buff *skb, struct net_device *dev)

 {

 	int len = 0;

 	struct ctcm_priv *priv = dev->ml_priv;