Re: [PATCH v3] ipc/shm: check shm_lock() in do_shmat cleanup

[Lorenzo Stoakes (ARM)]

On Thu, Jul 16, 2026 at 03:53:30PM +0800, Yi Xie wrote:
> do_shmat() calls shm_lock() in the out_nattch branch and
> immediately dereferences it, however shm_lock() can return an
> error.
>
> Check for an error and handle it if there is one.
>
> Signed-off-by: Yi Xie <xieyi@xxxxxxxxxx>

LGTM, so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>

> ---

Small note - it's useful to put a list of changes per version and links to the
previous versions on lore after the '---' for reviewers. Anything after the ---
and before the patch won't go upstream.

>  ipc/shm.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/ipc/shm.c b/ipc/shm.c
> index b3e8a58e177d..d243137c4dbd 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -1677,12 +1677,16 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg,
>  out_nattch:
>  	down_write(&shm_ids(ns).rwsem);
>  	shp = shm_lock(ns, shmid);
> -	shp->shm_nattch--;
> +	if (IS_ERR(shp)) {
> +		err = PTR_ERR(shp);
> +	} else {
> +		shp->shm_nattch--;
>
> -	if (shm_may_destroy(shp))
> -		shm_destroy(ns, shp);
> -	else
> -		shm_unlock(shp);
> +		if (shm_may_destroy(shp))
> +			shm_destroy(ns, shp);
> +		else
> +			shm_unlock(shp);
> +	}
>  	up_write(&shm_ids(ns).rwsem);
>  	return err;
>
> --
> 2.25.1
>

Cheers, Lorenzo