[PATCH] net: ethernet: ti: Fix return type of netcp_ndo_start_xmit()

[PATCH] net: ethernet: ti: Fix return type of netcp_ndo_start_xmit()

[Nathan Chancellor]

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/net/ethernet/ti/netcp_core.c:1944:21: 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         = netcp_ndo_start_xmit,
                                    ^~~~~~~~~~~~~~~~~~~~
  1 error generated.

->ndo_start_xmit() in 'struct net_device_ops' expects a return type of
'netdev_tx_t', not 'int'. Adjust the return type of
netcp_ndo_start_xmit() to match the prototype's to resolve the warning
and CFI failure.

Link: https://github.com/ClangBuiltLinux/linux/issues/1750
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 drivers/net/ethernet/ti/netcp_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/ti/netcp_core.c b/drivers/net/ethernet/ti/netcp_core.c
index aba70bef4894..9eb9eaff4dc9 100644
--- a/drivers/net/ethernet/ti/netcp_core.c
+++ b/drivers/net/ethernet/ti/netcp_core.c
@@ -1261,7 +1261,7 @@ static int netcp_tx_submit_skb(struct netcp_intf *netcp,
 }
 
 /* Submit the packet */
-static int netcp_ndo_start_xmit(struct sk_buff *skb, struct net_device *ndev)
+static netdev_tx_t netcp_ndo_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 {
 	struct netcp_intf *netcp = netdev_priv(ndev);
 	struct netcp_stats *tx_stats = &netcp->stats;

base-commit: 9abf2313adc1ca1b6180c508c25f22f9395cc780
-- 
2.38.1

Re: [PATCH] net: ethernet: ti: Fix return type of netcp_ndo_start_xmit()

[Kees Cook]

On Wed, Nov 02, 2022 at 09:09:33AM -0700, Nathan Chancellor wrote:
> 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/net/ethernet/ti/netcp_core.c:1944:21: 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         = netcp_ndo_start_xmit,
>                                     ^~~~~~~~~~~~~~~~~~~~
>   1 error generated.
> 
> ->ndo_start_xmit() in 'struct net_device_ops' expects a return type of
> 'netdev_tx_t', not 'int'. Adjust the return type of
> netcp_ndo_start_xmit() to match the prototype's to resolve the warning
> and CFI failure.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1750
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

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

-- 
Kees Cook

Re: [PATCH] net: ethernet: ti: Fix return type of netcp_ndo_start_xmit()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Wed,  2 Nov 2022 09:09:33 -0700 you wrote:
> 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:
> 
> [...]

Here is the summary with links:
  - net: ethernet: ti: Fix return type of netcp_ndo_start_xmit()
    https://git.kernel.org/netdev/net-next/c/63fe6ff674a9

You are awesome, thank you!
-- 
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