Re: [PATCH] nvmet: Don't overflow subsysnqn

[Christoph Hellwig]

On Tue, Dec 17, 2024 at 04:59:10PM -0800, Leo Stone wrote:
> nvmet_root_discovery_nqn_store treats the subsysnqn string like a fixed
> size buffer, even though it is dynamically allocated to the size of the
> string.
> 
> Create a new string with kstrdup instead of using the old buffer.
> 
> Reported-by: syzbot+ff4aab278fa7e27e0f9e@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=ff4aab278fa7e27e0f9e
> Fixes: 95409e277d83 ("nvmet: implement unique discovery NQN")
> Signed-off-by: Leo Stone <leocstone@xxxxxxxxx>
> ---
>  drivers/nvme/target/configfs.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/nvme/target/configfs.c b/drivers/nvme/target/configfs.c
> index eeee9e9b854c..3fa25f9f7d92 100644
> --- a/drivers/nvme/target/configfs.c
> +++ b/drivers/nvme/target/configfs.c
> @@ -2271,8 +2271,8 @@ static ssize_t nvmet_root_discovery_nqn_store(struct config_item *item,
>  			return -EINVAL;
>  		}
>  	}
> -	memset(nvmet_disc_subsys->subsysnqn, 0, NVMF_NQN_FIELD_LEN);
> -	memcpy(nvmet_disc_subsys->subsysnqn, page, len);
> +	kfree(nvmet_disc_subsys->subsysnqn);
> +	nvmet_disc_subsys->subsysnqn = kstrdup(page, GFP_KERNEL);

This needs error handling, pobably best done by using a local
variable for the new allocation, which would also help to keep it
outside the lock.