The driver was using devm_register_netdev() which causes unregister_netdev()
to be deferred until the devres cleanup phase, which runs after emac_remove()
returns. This creates a use-after-free window where:

1. emac_remove() is called, which tears down hardware (cancels work, detaches
   modules, unregisters from MAL)
2. emac_remove() returns
3. devres cleanup runs and finally calls unregister_netdev()

During step 3, the network stack might still process packets, triggering
emac_irq(), emac_poll(), or other handlers that access now-freed hardware
resources (dev->emacp, dev->mal, etc.).

Fix this by replacing devm_register_netdev() with manual register_netdev()
and calling unregister_netdev() at the beginning of emac_remove(), before
any hardware teardown. This ensures the network device is fully stopped and
unregistered before hardware resources are released.

The change is safe because:
- dev->ndev is assigned very early in probe (before any error paths that
  could bypass emac_remove)
- platform_set_drvdata() is only called after successful registration, so
  emac_remove() only runs for fully registered devices
- unregister_netdev() is idempotent and safe to call on any registered device

Fixes: a4dd8535a527 ("net: ibm: emac: use devm for register_netdev")
Assisted-by: opencode:big-pickle
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 drivers/net/ethernet/ibm/emac/core.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/ibm/emac/core.c b/drivers/net/ethernet/ibm/emac/core.c
index d9bbcfbcf60e..00a36c839d82 100644
--- a/drivers/net/ethernet/ibm/emac/core.c
+++ b/drivers/net/ethernet/ibm/emac/core.c
@@ -3151,7 +3151,7 @@ static int emac_probe(struct platform_device *ofdev)

 	netif_carrier_off(ndev);

-	err = devm_register_netdev(&ofdev->dev, ndev);
+	err = register_netdev(ndev);
 	if (err) {
 		printk(KERN_ERR "%pOF: failed to register net device (%d)!\n",
 		       np, err);
@@ -3204,6 +3204,13 @@ static void emac_remove(struct platform_device *ofdev)

 	DBG(dev, "remove" NL);

+	/* Unregister network device before tearing down hardware
+	 * to prevent use-after-free during deferred cleanup. This ensures
+	 * the network stack stops all operations before hardware resources
+	 * are released.
+	 */
+	unregister_netdev(dev->ndev);
+
 	cancel_work_sync(&dev->reset_work);

 	if (emac_has_feature(dev, EMAC_FTR_HAS_TAH))
--
2.54.0

On 6/3/2026 3:12 PM, Rosen Penev wrote:
> The driver was using devm_register_netdev() which causes unregister_netdev()
> to be deferred until the devres cleanup phase, which runs after emac_remove()
> returns. This creates a use-after-free window where:
> 
> 1. emac_remove() is called, which tears down hardware (cancels work, detaches
>    modules, unregisters from MAL)
> 2. emac_remove() returns
> 3. devres cleanup runs and finally calls unregister_netdev()
> 
> During step 3, the network stack might still process packets, triggering
> emac_irq(), emac_poll(), or other handlers that access now-freed hardware
> resources (dev->emacp, dev->mal, etc.).
> 
> Fix this by replacing devm_register_netdev() with manual register_netdev()
> and calling unregister_netdev() at the beginning of emac_remove(), before
> any hardware teardown. This ensures the network device is fully stopped and
> unregistered before hardware resources are released.
> 
> The change is safe because:
> - dev->ndev is assigned very early in probe (before any error paths that
>   could bypass emac_remove)
> - platform_set_drvdata() is only called after successful registration, so
>   emac_remove() only runs for fully registered devices
> - unregister_netdev() is idempotent and safe to call on any registered device
> 
> Fixes: a4dd8535a527 ("net: ibm: emac: use devm for register_netdev")
> Assisted-by: opencode:big-pickle
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
>  drivers/net/ethernet/ibm/emac/core.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/ibm/emac/core.c b/drivers/net/ethernet/ibm/emac/core.c
> index d9bbcfbcf60e..00a36c839d82 100644
> --- a/drivers/net/ethernet/ibm/emac/core.c
> +++ b/drivers/net/ethernet/ibm/emac/core.c
> @@ -3151,7 +3151,7 @@ static int emac_probe(struct platform_device *ofdev)
> 
>  	netif_carrier_off(ndev);
> 
> -	err = devm_register_netdev(&ofdev->dev, ndev);
> +	err = register_netdev(ndev);
>  	if (err) {

Right. The way devm_register_netdev *would* be safe is if everything
that depends on the netdev being registered also be a devm action (since
the devm cleanup actions get executed in reverse order).

Since a bunch of stuff that the netdev depends on is cleaned up normally
in emac_probe, things break.

Makes sense.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>

>  		printk(KERN_ERR "%pOF: failed to register net device (%d)!\n",
>  		       np, err);
> @@ -3204,6 +3204,13 @@ static void emac_remove(struct platform_device *ofdev)
> 
>  	DBG(dev, "remove" NL);
> 
> +	/* Unregister network device before tearing down hardware
> +	 * to prevent use-after-free during deferred cleanup. This ensures
> +	 * the network stack stops all operations before hardware resources
> +	 * are released.
> +	 */
> +	unregister_netdev(dev->ndev);
> +
>  	cancel_work_sync(&dev->reset_work);
> 
>  	if (emac_has_feature(dev, EMAC_FTR_HAS_TAH))
> --
> 2.54.0
> 
>