`css_alloc_subchannel()` calls `device_initialize()` before setting up
the DMA masks. If `dma_set_coherent_mask()` or `dma_set_mask()` fails,
the error path frees the subchannel structure directly, bypassing
the device model reference counting.

Once `device_initialize()` has been called, the embedded struct device
must be released via `put_device()`, allowing the release callback to
free the container structure.

Fix the error path by dropping the initial device reference with
`put_device()` instead of calling `kfree()` directly.

This ensures correct device lifetime handling and avoids potential
use-after-free or double-free issues.

Fixes: e5dcf0025d7af ("s390/css: move subchannel lock allocation")

Signed-off-by: Salah Triki <salah.triki@gmail.com>
---
 drivers/s390/cio/css.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index 4c85df7a548e..ac24e019020e 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -235,7 +235,7 @@ struct subchannel *css_alloc_subchannel(struct subchannel_id schid,
 	return sch;
 
 err:
-	kfree(sch);
+	put_device(&sch->dev);
 	return ERR_PTR(ret);
 }
 
-- 
2.43.0

On Fri, Jan 30, 2026 at 09:47:59PM +0100, Salah Triki wrote:
> `css_alloc_subchannel()` calls `device_initialize()` before setting up
> the DMA masks. If `dma_set_coherent_mask()` or `dma_set_mask()` fails,
> the error path frees the subchannel structure directly, bypassing
> the device model reference counting.
> 
> Once `device_initialize()` has been called, the embedded struct device
> must be released via `put_device()`, allowing the release callback to
> free the container structure.
> 
> Fix the error path by dropping the initial device reference with
> `put_device()` instead of calling `kfree()` directly.
> 
> This ensures correct device lifetime handling and avoids potential
> use-after-free or double-free issues.
> 
> Fixes: e5dcf0025d7af ("s390/css: move subchannel lock allocation")
> 
> Signed-off-by: Salah Triki <salah.triki@gmail.com>
> ---
>  drivers/s390/cio/css.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Applied, thanks.

On 1/30/26 21:47, Salah Triki wrote:
> `css_alloc_subchannel()` calls `device_initialize()` before setting up
> the DMA masks. If `dma_set_coherent_mask()` or `dma_set_mask()` fails,
> the error path frees the subchannel structure directly, bypassing
> the device model reference counting.
> 
> Once `device_initialize()` has been called, the embedded struct device
> must be released via `put_device()`, allowing the release callback to
> free the container structure.
> 
> Fix the error path by dropping the initial device reference with
> `put_device()` instead of calling `kfree()` directly.
> 
> This ensures correct device lifetime handling and avoids potential
> use-after-free or double-free issues.
> 
> Fixes: e5dcf0025d7af ("s390/css: move subchannel lock allocation")
> 
> Signed-off-by: Salah Triki<salah.triki@gmail.com>
> ---

Thank you.
this looks good to me.

Reviewed-by: Vineeth Vijayan <vneethv@linux.ibm.com>