Subject: Re: [PATCH v3] sctp: Add peeloff-flags socket option

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Sat, 1 Jul 2017 14:29:19 -0300

On Fri, Jun 30, 2017 at 01:32:57PM -0400, Neil Horman wrote:
> Based on a request raised on the sctp devel list, there is a need to
> augment the sctp_peeloff operation while specifying the O_CLOEXEC and
> O_NONBLOCK flags (simmilar to the socket syscall).  Since modifying the
> SCTP_SOCKOPT_PEELOFF socket option would break user space ABI for existing
> programs, this patch creates a new socket option
> SCTP_SOCKOPT_PEELOFF_FLAGS, which accepts a third flags parameter to
> allow atomic assignment of the socket descriptor flags.
> 
> Tested successfully by myself and the requestor
> 
> Signed-off-by: Neil Horman <[email-masked]>
> CC: Vlad Yasevich <[email-masked]>
> CC: "David S. Miller" <[email-masked]>
> CC: Andreas Steinmetz <[email-masked]>
> CC: Marcelo Ricardo Leitner <[email-masked]>

Acked-by: Marcelo Ricardo Leitner <[email-masked]>

Thanks!

> 
> ---
> Change notes:
> 
> v2)
> 
> * Per Marcellos comments, move to use of get_unused_fd_flags() and
> clean up code to independently set CLOEXEC
> 
> * clean up a stray tab
> 
> v3)
> 
> * Clean up some long lines
> ---
>  include/uapi/linux/sctp.h |  6 ++++
>  net/sctp/socket.c         | 87 +++++++++++++++++++++++++++++++++++++++--------
>  2 files changed, 78 insertions(+), 15 deletions(-)
> 
> diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> index ced9d8b..6217ff8 100644
> --- a/include/uapi/linux/sctp.h
> +++ b/include/uapi/linux/sctp.h
> @@ -121,6 +121,7 @@ typedef __s32 sctp_assoc_t;
>  #define SCTP_RESET_STREAMS	119
>  #define SCTP_RESET_ASSOC	120
>  #define SCTP_ADD_STREAMS	121
> +#define SCTP_SOCKOPT_PEELOFF_FLAGS 122
>  
>  /* PR-SCTP policies */
>  #define SCTP_PR_SCTP_NONE	0x0000
> @@ -978,6 +979,11 @@ typedef struct {
>  	int sd;
>  } sctp_peeloff_arg_t;
>  
> +typedef struct {
> +	sctp_peeloff_arg_t p_arg;
> +	unsigned flags;
> +} sctp_peeloff_flags_arg_t;
> +
>  /*
>   *  Peer Address Thresholds socket option
>   */
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index 7b6e20e..72de049 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -4933,11 +4933,47 @@ int sctp_do_peeloff(struct sock *sk, sctp_assoc_t id, struct socket **sockp)
>  }
>  EXPORT_SYMBOL(sctp_do_peeloff);
>  
> +static int sctp_getsockopt_peeloff_common(struct sock *sk, sctp_peeloff_arg_t *peeloff,
> +					  struct file **newfile, unsigned flags)
> +{
> +	struct socket *newsock;
> +	int retval;
> +
> +	retval = sctp_do_peeloff(sk, peeloff->associd, &newsock);
> +	if (retval < 0)
> +		goto out;
> +
> +	/* Map the socket to an unused fd that can be returned to the user.  */
> +	retval = get_unused_fd_flags(flags & SOCK_CLOEXEC);
> +	if (retval < 0) {
> +		sock_release(newsock);
> +		goto out;
> +	}
> +
> +	*newfile = sock_alloc_file(newsock, 0, NULL);
> +	if (IS_ERR(*newfile)) {
> +		put_unused_fd(retval);
> +		sock_release(newsock);
> +		retval = PTR_ERR(*newfile);
> +		*newfile = NULL;
> +		return retval;
> +	}
> +
> +	pr_debug("%s: sk:%p, newsk:%p, sd:%d\n", __func__, sk, newsock->sk,
> +		 retval);
> +
> +	peeloff->sd = retval;
> +
> +	if (flags & SOCK_NONBLOCK)
> +		(*newfile)->f_flags |= O_NONBLOCK;
> +out:
> +	return retval;
> +}
> +
>  static int sctp_getsockopt_peeloff(struct sock *sk, int len, char __user *optval, int __user *optlen)
>  {
>  	sctp_peeloff_arg_t peeloff;
> -	struct socket *newsock;
> -	struct file *newfile;
> +	struct file *newfile = NULL;
>  	int retval = 0;
>  
>  	if (len < sizeof(sctp_peeloff_arg_t))
> @@ -4946,26 +4982,44 @@ static int sctp_getsockopt_peeloff(struct sock *sk, int len, char __user *optval
>  	if (copy_from_user(&peeloff, optval, len))
>  		return -EFAULT;
>  
> -	retval = sctp_do_peeloff(sk, peeloff.associd, &newsock);
> +	retval = sctp_getsockopt_peeloff_common(sk, &peeloff, &newfile, 0);
>  	if (retval < 0)
>  		goto out;
>  
> -	/* Map the socket to an unused fd that can be returned to the user.  */
> -	retval = get_unused_fd_flags(0);
> -	if (retval < 0) {
> -		sock_release(newsock);
> -		goto out;
> +	/* Return the fd mapped to the new socket.  */
> +	if (put_user(len, optlen)) {
> +		fput(newfile);
> +		put_unused_fd(retval);
> +		return -EFAULT;
>  	}
>  
> -	newfile = sock_alloc_file(newsock, 0, NULL);
> -	if (IS_ERR(newfile)) {
> +	if (copy_to_user(optval, &peeloff, len)) {
> +		fput(newfile);
>  		put_unused_fd(retval);
> -		sock_release(newsock);
> -		return PTR_ERR(newfile);
> +		return -EFAULT;
>  	}
> +	fd_install(retval, newfile);
> +out:
> +	return retval;
> +}
>  
> -	pr_debug("%s: sk:%p, newsk:%p, sd:%d\n", __func__, sk, newsock->sk,
> -		 retval);
> +static int sctp_getsockopt_peeloff_flags(struct sock *sk, int len,
> +					 char __user *optval, int __user *optlen)
> +{
> +	sctp_peeloff_flags_arg_t peeloff;
> +	struct file *newfile = NULL;
> +	int retval = 0;
> +
> +	if (len < sizeof(sctp_peeloff_flags_arg_t))
> +		return -EINVAL;
> +	len = sizeof(sctp_peeloff_flags_arg_t);
> +	if (copy_from_user(&peeloff, optval, len))
> +		return -EFAULT;
> +
> +	retval = sctp_getsockopt_peeloff_common(sk, &peeloff.p_arg,
> +						&newfile, peeloff.flags);
> +	if (retval < 0)
> +		goto out;
>  
>  	/* Return the fd mapped to the new socket.  */
>  	if (put_user(len, optlen)) {
> @@ -4973,7 +5027,7 @@ static int sctp_getsockopt_peeloff(struct sock *sk, int len, char __user *optval
>  		put_unused_fd(retval);
>  		return -EFAULT;
>  	}
> -	peeloff.sd = retval;
> +
>  	if (copy_to_user(optval, &peeloff, len)) {
>  		fput(newfile);
>  		put_unused_fd(retval);
> @@ -6758,6 +6812,9 @@ static int sctp_getsockopt(struct sock *sk, int level, int optname,
>  	case SCTP_SOCKOPT_PEELOFF:
>  		retval = sctp_getsockopt_peeloff(sk, len, optval, optlen);
>  		break;
> +	case SCTP_SOCKOPT_PEELOFF_FLAGS:
> +		retval = sctp_getsockopt_peeloff_flags(sk, len, optval, optlen);
> +		break;
>  	case SCTP_PEER_ADDR_PARAMS:
>  		retval = sctp_getsockopt_peer_addr_params(sk, len, optval,
>  							  optlen);
> -- 
> 2.9.4
> 
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