Re: [PATCH v10 3/4] liveupdate: add LIVEUPDATE_SESSION_GET_NAME ioctl

[Pratyush Yadav <pratyush@kernel.org>]

On Fri, Apr 24 2026, luca.boccassi@gmail.com wrote:

> From: Luca Boccassi <luca.boccassi@gmail.com>
>
> Userspace when requesting a session via the ioctl specifies a name and
> gets a FD, but then there is no ioctl to go back the other way and get
> the name given a LUO session FD. This is problematic especially when
> there is a userspace orchestrator that wants to check what FDs it is
> handling for clients without having to do manual string scraping of
> procfs, or without procfs at all.
>
> Add a ioctl to simply get the name from an FD.
>
> Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
> Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
>  include/uapi/linux/liveupdate.h | 21 +++++++++++++++++++++
>  kernel/liveupdate/luo_session.c | 13 +++++++++++++
>  2 files changed, 34 insertions(+)
>
> diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h
> index 30bc66ee9436..3a9ff53b02e0 100644
> --- a/include/uapi/linux/liveupdate.h
> +++ b/include/uapi/linux/liveupdate.h
> @@ -59,6 +59,7 @@ enum {
>  	LIVEUPDATE_CMD_SESSION_PRESERVE_FD = LIVEUPDATE_CMD_SESSION_BASE,
>  	LIVEUPDATE_CMD_SESSION_RETRIEVE_FD = 0x41,
>  	LIVEUPDATE_CMD_SESSION_FINISH = 0x42,
> +	LIVEUPDATE_CMD_SESSION_GET_NAME = 0x43,
>  };
>  
>  /**
> @@ -213,4 +214,24 @@ struct liveupdate_session_finish {
>  #define LIVEUPDATE_SESSION_FINISH					\
>  	_IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_FINISH)
>  
> +/**
> + * struct liveupdate_session_get_name - ioctl(LIVEUPDATE_SESSION_GET_NAME)
> + * @size:  Input; sizeof(struct liveupdate_session_get_name)
> + * @reserved: Input; Must be zero. Reserved for future use.

You need to enforce this in luo_session_get_name(). Otherwise some
userspace might try to get clever and stash some data here. Then if we
ever put something else here it will break that userspace.

With this fixed,

Reviewed-by: Pratyush Yadav <pratyush@kernel.org>

> + * @name:  Output; A null-terminated string with the full session name.
> + *
> + * Retrieves the full name of the session associated with this file descriptor.
> + * This is useful because the kernel may truncate the name shown in /proc.
> + *
> + * Return: 0 on success, negative error code on failure.
> + */
> +struct liveupdate_session_get_name {
> +	__u32		size;
> +	__u32		reserved;
> +	__u8		name[LIVEUPDATE_SESSION_NAME_LENGTH];
> +};
> +
> +#define LIVEUPDATE_SESSION_GET_NAME					\
> +	_IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_GET_NAME)
> +
>  #endif /* _UAPI_LIVEUPDATE_H */
> diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
> index 5e316a4c5d71..0bcf2def074e 100644
> --- a/kernel/liveupdate/luo_session.c
> +++ b/kernel/liveupdate/luo_session.c
> @@ -289,10 +289,21 @@ static int luo_session_finish(struct luo_session *session,
>  	return luo_ucmd_respond(ucmd, sizeof(*argp));
>  }
>  
> +static int luo_session_get_name(struct luo_session *session,
> +				struct luo_ucmd *ucmd)
> +{
> +	struct liveupdate_session_get_name *argp = ucmd->cmd;
> +
> +	strscpy((char *)argp->name, session->name, sizeof(argp->name));
> +
> +	return luo_ucmd_respond(ucmd, sizeof(*argp));
> +}
> +
>  union ucmd_buffer {
>  	struct liveupdate_session_finish finish;
>  	struct liveupdate_session_preserve_fd preserve;
>  	struct liveupdate_session_retrieve_fd retrieve;
> +	struct liveupdate_session_get_name get_name;
>  };
>  
>  struct luo_ioctl_op {
> @@ -319,6 +330,8 @@ static const struct luo_ioctl_op luo_session_ioctl_ops[] = {
>  		 struct liveupdate_session_preserve_fd, token),
>  	IOCTL_OP(LIVEUPDATE_SESSION_RETRIEVE_FD, luo_session_retrieve_fd,
>  		 struct liveupdate_session_retrieve_fd, token),
> +	IOCTL_OP(LIVEUPDATE_SESSION_GET_NAME, luo_session_get_name,
> +		 struct liveupdate_session_get_name, name),
>  };
>  
>  static long luo_session_ioctl(struct file *filep, unsigned int cmd,

-- 
Regards,
Pratyush Yadav