[v4,02/11] fs: Move __scm_install_fd() to __fd_install_received()
diff mbox series

Message ID 20200616032524.460144-3-keescook@chromium.org
State New
Headers show
Series
  • Add seccomp notifier ioctl that enables adding fds
Related show

Commit Message

Kees Cook June 16, 2020, 3:25 a.m. UTC
In preparation for users of the "install a received file" logic outside
of net/ (pidfd and seccomp), relocate and rename __scm_install_fd() from
net/core/scm.c to __fd_install_received() in fs/file.c, and provide a
wrapper named fd_install_received_user(), as future patches will change
the interface to __fd_install_received().

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 fs/file.c            | 47 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/file.h |  8 ++++++++
 include/net/scm.h    |  1 -
 net/compat.c         |  2 +-
 net/core/scm.c       | 32 +-----------------------------
 5 files changed, 57 insertions(+), 33 deletions(-)

Comments

Sargun Dhillon June 16, 2020, 5:29 a.m. UTC | #1
On Mon, Jun 15, 2020 at 08:25:15PM -0700, Kees Cook wrote:
> In preparation for users of the "install a received file" logic outside
> of net/ (pidfd and seccomp), relocate and rename __scm_install_fd() from
> net/core/scm.c to __fd_install_received() in fs/file.c, and provide a
> wrapper named fd_install_received_user(), as future patches will change
> the interface to __fd_install_received().
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  fs/file.c            | 47 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/file.h |  8 ++++++++
>  include/net/scm.h    |  1 -
>  net/compat.c         |  2 +-
>  net/core/scm.c       | 32 +-----------------------------
>  5 files changed, 57 insertions(+), 33 deletions(-)
> 
> diff --git a/fs/file.c b/fs/file.c
> index abb8b7081d7a..fcfddae0d252 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -11,6 +11,7 @@
>  #include <linux/export.h>
>  #include <linux/fs.h>
>  #include <linux/mm.h>
> +#include <linux/net.h>
>  #include <linux/sched/signal.h>
>  #include <linux/slab.h>
>  #include <linux/file.h>
> @@ -18,6 +19,8 @@
>  #include <linux/bitops.h>
>  #include <linux/spinlock.h>
>  #include <linux/rcupdate.h>
> +#include <net/cls_cgroup.h>
> +#include <net/netprio_cgroup.h>
>  
>  unsigned int sysctl_nr_open __read_mostly = 1024*1024;
>  unsigned int sysctl_nr_open_min = BITS_PER_LONG;
> @@ -931,6 +934,50 @@ int replace_fd(unsigned fd, struct file *file, unsigned flags)
>  	return err;
>  }
>  
> +/**
> + * __fd_install_received() - Install received file into file descriptor table
> + *
> + * @fd: fd to install into (if negative, a new fd will be allocated)
> + * @file: struct file that was received from another process
> + * @ufd_required: true to use @ufd for writing fd number to userspace
> + * @ufd: __user pointer to write new fd number to
> + * @o_flags: the O_* flags to apply to the new fd entry
Probably doesn't matter, but this function doesn't take the fd, or ufd_required
argument in this patch. 

> + *
> + * Installs a received file into the file descriptor table, with appropriate
> + * checks and count updates. Optionally writes the fd number to userspace.
ufd does not apppear options here.

> + *
> + * Returns -ve on error.
> + */
> +int __fd_install_received(struct file *file, int __user *ufd, unsigned int o_flags)
> +{
> +	struct socket *sock;
> +	int new_fd;
> +	int error;
> +
> +	error = security_file_receive(file);
> +	if (error)
> +		return error;
> +
> +	new_fd = get_unused_fd_flags(o_flags);
> +	if (new_fd < 0)
> +		return new_fd;
> +
> +	error = put_user(new_fd, ufd);
> +	if (error) {
> +		put_unused_fd(new_fd);
> +		return error;
> +	}
> +
> +	/* Bump the usage count and install the file. */
> +	sock = sock_from_file(file, &error);
> +	if (sock) {
> +		sock_update_netprioidx(&sock->sk->sk_cgrp_data);
> +		sock_update_classid(&sock->sk->sk_cgrp_data);
> +	}
> +	fd_install(new_fd, get_file(file));
> +	return 0;
> +}
> +
>  static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
>  {
>  	int err = -EBADF;
> diff --git a/include/linux/file.h b/include/linux/file.h
> index 122f80084a3e..fe18a1a0d555 100644
> --- a/include/linux/file.h
> +++ b/include/linux/file.h
> @@ -91,6 +91,14 @@ extern void put_unused_fd(unsigned int fd);
>  
>  extern void fd_install(unsigned int fd, struct file *file);
>  
> +extern int __fd_install_received(struct file *file, int __user *ufd,
> +				 unsigned int o_flags);
> +static inline int fd_install_received_user(struct file *file, int __user *ufd,
> +					   unsigned int o_flags)
> +{
> +	return __fd_install_received(file, ufd, o_flags);
> +}
> +
>  extern void flush_delayed_fput(void);
>  extern void __fput_sync(struct file *);
>  
> diff --git a/include/net/scm.h b/include/net/scm.h
> index 581a94d6c613..1ce365f4c256 100644
> --- a/include/net/scm.h
> +++ b/include/net/scm.h
> @@ -37,7 +37,6 @@ struct scm_cookie {
>  #endif
>  };
>  
> -int __scm_install_fd(struct file *file, int __user *ufd, unsigned int o_flags);
>  void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm);
>  void scm_detach_fds_compat(struct msghdr *msg, struct scm_cookie *scm);
>  int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm);
> diff --git a/net/compat.c b/net/compat.c
> index 27d477fdcaa0..94f288e8dac5 100644
> --- a/net/compat.c
> +++ b/net/compat.c
> @@ -298,7 +298,7 @@ void scm_detach_fds_compat(struct msghdr *msg, struct scm_cookie *scm)
>  	int err = 0, i;
>  
>  	for (i = 0; i < fdmax; i++) {
> -		err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
> +		err = fd_install_received_user(scm->fp->fp[i], cmsg_data + i, o_flags);
>  		if (err)
>  			break;
>  	}
> diff --git a/net/core/scm.c b/net/core/scm.c
> index 6151678c73ed..df190f1fdd28 100644
> --- a/net/core/scm.c
> +++ b/net/core/scm.c
> @@ -280,36 +280,6 @@ void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_inter
>  }
>  EXPORT_SYMBOL(put_cmsg_scm_timestamping);
>  
> -int __scm_install_fd(struct file *file, int __user *ufd, unsigned int o_flags)
> -{
> -	struct socket *sock;
> -	int new_fd;
> -	int error;
> -
> -	error = security_file_receive(file);
> -	if (error)
> -		return error;
> -
> -	new_fd = get_unused_fd_flags(o_flags);
> -	if (new_fd < 0)
> -		return new_fd;
> -
> -	error = put_user(new_fd, ufd);
> -	if (error) {
> -		put_unused_fd(new_fd);
> -		return error;
> -	}
> -
> -	/* Bump the usage count and install the file. */
> -	sock = sock_from_file(file, &error);
> -	if (sock) {
> -		sock_update_netprioidx(&sock->sk->sk_cgrp_data);
> -		sock_update_classid(&sock->sk->sk_cgrp_data);
> -	}
> -	fd_install(new_fd, get_file(file));
> -	return 0;
> -}
> -
>  static int scm_max_fds(struct msghdr *msg)
>  {
>  	if (msg->msg_controllen <= sizeof(struct cmsghdr))
> @@ -336,7 +306,7 @@ void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
>  	}
>  
>  	for (i = 0; i < fdmax; i++) {
> -		err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
> +		err = fd_install_received_user(scm->fp->fp[i], cmsg_data + i, o_flags);
>  		if (err)
>  			break;
>  	}
> -- 
> 2.25.1
>
Kees Cook June 16, 2020, 5:48 a.m. UTC | #2
On Tue, Jun 16, 2020 at 05:29:41AM +0000, Sargun Dhillon wrote:
> On Mon, Jun 15, 2020 at 08:25:15PM -0700, Kees Cook wrote:
> > +/**
> > + * __fd_install_received() - Install received file into file descriptor table
> > + *
> > + * @fd: fd to install into (if negative, a new fd will be allocated)
> > + * @file: struct file that was received from another process
> > + * @ufd_required: true to use @ufd for writing fd number to userspace
> > + * @ufd: __user pointer to write new fd number to
> > + * @o_flags: the O_* flags to apply to the new fd entry
> Probably doesn't matter, but this function doesn't take the fd, or ufd_required
> argument in this patch. 
> 
> > + *
> > + * Installs a received file into the file descriptor table, with appropriate
> > + * checks and count updates. Optionally writes the fd number to userspace.
> ufd does not apppear options here.

Argh, yes, thanks. I think this was a fixup targeting the wrong commit.
I will adjust.
David Laight June 17, 2020, 3:25 p.m. UTC | #3
From: Kees Cook
> Sent: 16 June 2020 04:25
 
> In preparation for users of the "install a received file" logic outside
> of net/ (pidfd and seccomp), relocate and rename __scm_install_fd() from
> net/core/scm.c to __fd_install_received() in fs/file.c, and provide a
> wrapper named fd_install_received_user(), as future patches will change
> the interface to __fd_install_received().

Any reason for the leading __ ??

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
Kees Cook June 17, 2020, 6:40 p.m. UTC | #4
On Wed, Jun 17, 2020 at 03:25:41PM +0000, David Laight wrote:
> From: Kees Cook
> > Sent: 16 June 2020 04:25
>  
> > In preparation for users of the "install a received file" logic outside
> > of net/ (pidfd and seccomp), relocate and rename __scm_install_fd() from
> > net/core/scm.c to __fd_install_received() in fs/file.c, and provide a
> > wrapper named fd_install_received_user(), as future patches will change
> > the interface to __fd_install_received().
> 
> Any reason for the leading __ ??

Mainly because of the code pattern of only using the inline helpers to
call it.
Christian Brauner June 18, 2020, 8:56 a.m. UTC | #5
On Mon, Jun 15, 2020 at 08:25:15PM -0700, Kees Cook wrote:
> In preparation for users of the "install a received file" logic outside
> of net/ (pidfd and seccomp), relocate and rename __scm_install_fd() from
> net/core/scm.c to __fd_install_received() in fs/file.c, and provide a
> wrapper named fd_install_received_user(), as future patches will change
> the interface to __fd_install_received().
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  fs/file.c            | 47 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/file.h |  8 ++++++++
>  include/net/scm.h    |  1 -
>  net/compat.c         |  2 +-
>  net/core/scm.c       | 32 +-----------------------------
>  5 files changed, 57 insertions(+), 33 deletions(-)
> 
> diff --git a/fs/file.c b/fs/file.c
> index abb8b7081d7a..fcfddae0d252 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -11,6 +11,7 @@
>  #include <linux/export.h>
>  #include <linux/fs.h>
>  #include <linux/mm.h>
> +#include <linux/net.h>
>  #include <linux/sched/signal.h>
>  #include <linux/slab.h>
>  #include <linux/file.h>
> @@ -18,6 +19,8 @@
>  #include <linux/bitops.h>
>  #include <linux/spinlock.h>
>  #include <linux/rcupdate.h>
> +#include <net/cls_cgroup.h>
> +#include <net/netprio_cgroup.h>
>  
>  unsigned int sysctl_nr_open __read_mostly = 1024*1024;
>  unsigned int sysctl_nr_open_min = BITS_PER_LONG;
> @@ -931,6 +934,50 @@ int replace_fd(unsigned fd, struct file *file, unsigned flags)
>  	return err;
>  }
>  
> +/**
> + * __fd_install_received() - Install received file into file descriptor table
> + *
> + * @fd: fd to install into (if negative, a new fd will be allocated)
> + * @file: struct file that was received from another process
> + * @ufd_required: true to use @ufd for writing fd number to userspace
> + * @ufd: __user pointer to write new fd number to
> + * @o_flags: the O_* flags to apply to the new fd entry
> + *
> + * Installs a received file into the file descriptor table, with appropriate
> + * checks and count updates. Optionally writes the fd number to userspace.
> + *
> + * Returns -ve on error.
> + */
> +int __fd_install_received(struct file *file, int __user *ufd, unsigned int o_flags)
> +{
> +	struct socket *sock;
> +	int new_fd;
> +	int error;
> +
> +	error = security_file_receive(file);
> +	if (error)
> +		return error;
> +
> +	new_fd = get_unused_fd_flags(o_flags);
> +	if (new_fd < 0)
> +		return new_fd;
> +
> +	error = put_user(new_fd, ufd);
> +	if (error) {
> +		put_unused_fd(new_fd);
> +		return error;
> +	}
> +
> +	/* Bump the usage count and install the file. */
> +	sock = sock_from_file(file, &error);
> +	if (sock) {
> +		sock_update_netprioidx(&sock->sk->sk_cgrp_data);
> +		sock_update_classid(&sock->sk->sk_cgrp_data);
> +	}
> +	fd_install(new_fd, get_file(file));
> +	return 0;
> +}
> +
>  static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
>  {
>  	int err = -EBADF;
> diff --git a/include/linux/file.h b/include/linux/file.h
> index 122f80084a3e..fe18a1a0d555 100644
> --- a/include/linux/file.h
> +++ b/include/linux/file.h
> @@ -91,6 +91,14 @@ extern void put_unused_fd(unsigned int fd);
>  
>  extern void fd_install(unsigned int fd, struct file *file);
>  
> +extern int __fd_install_received(struct file *file, int __user *ufd,
> +				 unsigned int o_flags);
> +static inline int fd_install_received_user(struct file *file, int __user *ufd,
> +					   unsigned int o_flags)
> +{
> +	return __fd_install_received(file, ufd, o_flags);
> +}

Shouldn't this be the other way around such that
fd_install_received_user() is the workhorse that has a "ufd" argument
and fd_install_received() is the static inline function that doesn't?

extern int fd_install_received_user(struct file *file, int __user *ufd, unsigned int o_flags)
static inline int fd_install_received(struct file *file, unsigned int o_flags)
{
	return fd_install_received_user(file, NULL, o_flags);
}

(So I'm on vacation this week some my reviews are selective and spotty
but I promise to be back next week. :))

Christian

> +
>  extern void flush_delayed_fput(void);
>  extern void __fput_sync(struct file *);
>  
> diff --git a/include/net/scm.h b/include/net/scm.h
> index 581a94d6c613..1ce365f4c256 100644
> --- a/include/net/scm.h
> +++ b/include/net/scm.h
> @@ -37,7 +37,6 @@ struct scm_cookie {
>  #endif
>  };
>  
> -int __scm_install_fd(struct file *file, int __user *ufd, unsigned int o_flags);
>  void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm);
>  void scm_detach_fds_compat(struct msghdr *msg, struct scm_cookie *scm);
>  int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm);
> diff --git a/net/compat.c b/net/compat.c
> index 27d477fdcaa0..94f288e8dac5 100644
> --- a/net/compat.c
> +++ b/net/compat.c
> @@ -298,7 +298,7 @@ void scm_detach_fds_compat(struct msghdr *msg, struct scm_cookie *scm)
>  	int err = 0, i;
>  
>  	for (i = 0; i < fdmax; i++) {
> -		err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
> +		err = fd_install_received_user(scm->fp->fp[i], cmsg_data + i, o_flags);
>  		if (err)
>  			break;
>  	}
> diff --git a/net/core/scm.c b/net/core/scm.c
> index 6151678c73ed..df190f1fdd28 100644
> --- a/net/core/scm.c
> +++ b/net/core/scm.c
> @@ -280,36 +280,6 @@ void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_inter
>  }
>  EXPORT_SYMBOL(put_cmsg_scm_timestamping);
>  
> -int __scm_install_fd(struct file *file, int __user *ufd, unsigned int o_flags)
> -{
> -	struct socket *sock;
> -	int new_fd;
> -	int error;
> -
> -	error = security_file_receive(file);
> -	if (error)
> -		return error;
> -
> -	new_fd = get_unused_fd_flags(o_flags);
> -	if (new_fd < 0)
> -		return new_fd;
> -
> -	error = put_user(new_fd, ufd);
> -	if (error) {
> -		put_unused_fd(new_fd);
> -		return error;
> -	}
> -
> -	/* Bump the usage count and install the file. */
> -	sock = sock_from_file(file, &error);
> -	if (sock) {
> -		sock_update_netprioidx(&sock->sk->sk_cgrp_data);
> -		sock_update_classid(&sock->sk->sk_cgrp_data);
> -	}
> -	fd_install(new_fd, get_file(file));
> -	return 0;
> -}
> -
>  static int scm_max_fds(struct msghdr *msg)
>  {
>  	if (msg->msg_controllen <= sizeof(struct cmsghdr))
> @@ -336,7 +306,7 @@ void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
>  	}
>  
>  	for (i = 0; i < fdmax; i++) {
> -		err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
> +		err = fd_install_received_user(scm->fp->fp[i], cmsg_data + i, o_flags);
>  		if (err)
>  			break;
>  	}
> -- 
> 2.25.1
>
Kees Cook June 18, 2020, 8:05 p.m. UTC | #6
On Thu, Jun 18, 2020 at 10:56:14AM +0200, Christian Brauner wrote:
> On Mon, Jun 15, 2020 at 08:25:15PM -0700, Kees Cook wrote:
> > In preparation for users of the "install a received file" logic outside
> > of net/ (pidfd and seccomp), relocate and rename __scm_install_fd() from
> > net/core/scm.c to __fd_install_received() in fs/file.c, and provide a
> > wrapper named fd_install_received_user(), as future patches will change
> > the interface to __fd_install_received().
> > 
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> >  fs/file.c            | 47 ++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/file.h |  8 ++++++++
> >  include/net/scm.h    |  1 -
> >  net/compat.c         |  2 +-
> >  net/core/scm.c       | 32 +-----------------------------
> >  5 files changed, 57 insertions(+), 33 deletions(-)
> > 
> > diff --git a/fs/file.c b/fs/file.c
> > index abb8b7081d7a..fcfddae0d252 100644
> > --- a/fs/file.c
> > +++ b/fs/file.c
> > @@ -11,6 +11,7 @@
> >  #include <linux/export.h>
> >  #include <linux/fs.h>
> >  #include <linux/mm.h>
> > +#include <linux/net.h>
> >  #include <linux/sched/signal.h>
> >  #include <linux/slab.h>
> >  #include <linux/file.h>
> > @@ -18,6 +19,8 @@
> >  #include <linux/bitops.h>
> >  #include <linux/spinlock.h>
> >  #include <linux/rcupdate.h>
> > +#include <net/cls_cgroup.h>
> > +#include <net/netprio_cgroup.h>
> >  
> >  unsigned int sysctl_nr_open __read_mostly = 1024*1024;
> >  unsigned int sysctl_nr_open_min = BITS_PER_LONG;
> > @@ -931,6 +934,50 @@ int replace_fd(unsigned fd, struct file *file, unsigned flags)
> >  	return err;
> >  }
> >  
> > +/**
> > + * __fd_install_received() - Install received file into file descriptor table
> > + *
> > + * @fd: fd to install into (if negative, a new fd will be allocated)
> > + * @file: struct file that was received from another process
> > + * @ufd_required: true to use @ufd for writing fd number to userspace
> > + * @ufd: __user pointer to write new fd number to
> > + * @o_flags: the O_* flags to apply to the new fd entry
> > + *
> > + * Installs a received file into the file descriptor table, with appropriate
> > + * checks and count updates. Optionally writes the fd number to userspace.
> > + *
> > + * Returns -ve on error.
> > + */
> > +int __fd_install_received(struct file *file, int __user *ufd, unsigned int o_flags)
> > +{
> > +	struct socket *sock;
> > +	int new_fd;
> > +	int error;
> > +
> > +	error = security_file_receive(file);
> > +	if (error)
> > +		return error;
> > +
> > +	new_fd = get_unused_fd_flags(o_flags);
> > +	if (new_fd < 0)
> > +		return new_fd;
> > +
> > +	error = put_user(new_fd, ufd);
> > +	if (error) {
> > +		put_unused_fd(new_fd);
> > +		return error;
> > +	}
> > +
> > +	/* Bump the usage count and install the file. */
> > +	sock = sock_from_file(file, &error);
> > +	if (sock) {
> > +		sock_update_netprioidx(&sock->sk->sk_cgrp_data);
> > +		sock_update_classid(&sock->sk->sk_cgrp_data);
> > +	}
> > +	fd_install(new_fd, get_file(file));
> > +	return 0;
> > +}
> > +
> >  static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
> >  {
> >  	int err = -EBADF;
> > diff --git a/include/linux/file.h b/include/linux/file.h
> > index 122f80084a3e..fe18a1a0d555 100644
> > --- a/include/linux/file.h
> > +++ b/include/linux/file.h
> > @@ -91,6 +91,14 @@ extern void put_unused_fd(unsigned int fd);
> >  
> >  extern void fd_install(unsigned int fd, struct file *file);
> >  
> > +extern int __fd_install_received(struct file *file, int __user *ufd,
> > +				 unsigned int o_flags);
> > +static inline int fd_install_received_user(struct file *file, int __user *ufd,
> > +					   unsigned int o_flags)
> > +{
> > +	return __fd_install_received(file, ufd, o_flags);
> > +}
> 
> Shouldn't this be the other way around such that
> fd_install_received_user() is the workhorse that has a "ufd" argument
> and fd_install_received() is the static inline function that doesn't?
> 
> extern int fd_install_received_user(struct file *file, int __user *ufd, unsigned int o_flags)
> static inline int fd_install_received(struct file *file, unsigned int o_flags)
> {
> 	return fd_install_received_user(file, NULL, o_flags);
> }

So, I think it's all worked out in v5[1], so the helper argument handling
is better for the ufd case, as David pointed out earlier. (As in,
I think you're reacting to the same general problem here.)

> (So I'm on vacation this week some my reviews are selective and spotty
> but I promise to be back next week. :))

No worries!

-Kees

[1] https://lore.kernel.org/lkml/20200617220327.3731559-1-keescook@chromium.org/

Patch
diff mbox series

diff --git a/fs/file.c b/fs/file.c
index abb8b7081d7a..fcfddae0d252 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -11,6 +11,7 @@ 
 #include <linux/export.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
+#include <linux/net.h>
 #include <linux/sched/signal.h>
 #include <linux/slab.h>
 #include <linux/file.h>
@@ -18,6 +19,8 @@ 
 #include <linux/bitops.h>
 #include <linux/spinlock.h>
 #include <linux/rcupdate.h>
+#include <net/cls_cgroup.h>
+#include <net/netprio_cgroup.h>
 
 unsigned int sysctl_nr_open __read_mostly = 1024*1024;
 unsigned int sysctl_nr_open_min = BITS_PER_LONG;
@@ -931,6 +934,50 @@  int replace_fd(unsigned fd, struct file *file, unsigned flags)
 	return err;
 }
 
+/**
+ * __fd_install_received() - Install received file into file descriptor table
+ *
+ * @fd: fd to install into (if negative, a new fd will be allocated)
+ * @file: struct file that was received from another process
+ * @ufd_required: true to use @ufd for writing fd number to userspace
+ * @ufd: __user pointer to write new fd number to
+ * @o_flags: the O_* flags to apply to the new fd entry
+ *
+ * Installs a received file into the file descriptor table, with appropriate
+ * checks and count updates. Optionally writes the fd number to userspace.
+ *
+ * Returns -ve on error.
+ */
+int __fd_install_received(struct file *file, int __user *ufd, unsigned int o_flags)
+{
+	struct socket *sock;
+	int new_fd;
+	int error;
+
+	error = security_file_receive(file);
+	if (error)
+		return error;
+
+	new_fd = get_unused_fd_flags(o_flags);
+	if (new_fd < 0)
+		return new_fd;
+
+	error = put_user(new_fd, ufd);
+	if (error) {
+		put_unused_fd(new_fd);
+		return error;
+	}
+
+	/* Bump the usage count and install the file. */
+	sock = sock_from_file(file, &error);
+	if (sock) {
+		sock_update_netprioidx(&sock->sk->sk_cgrp_data);
+		sock_update_classid(&sock->sk->sk_cgrp_data);
+	}
+	fd_install(new_fd, get_file(file));
+	return 0;
+}
+
 static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
 {
 	int err = -EBADF;
diff --git a/include/linux/file.h b/include/linux/file.h
index 122f80084a3e..fe18a1a0d555 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -91,6 +91,14 @@  extern void put_unused_fd(unsigned int fd);
 
 extern void fd_install(unsigned int fd, struct file *file);
 
+extern int __fd_install_received(struct file *file, int __user *ufd,
+				 unsigned int o_flags);
+static inline int fd_install_received_user(struct file *file, int __user *ufd,
+					   unsigned int o_flags)
+{
+	return __fd_install_received(file, ufd, o_flags);
+}
+
 extern void flush_delayed_fput(void);
 extern void __fput_sync(struct file *);
 
diff --git a/include/net/scm.h b/include/net/scm.h
index 581a94d6c613..1ce365f4c256 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -37,7 +37,6 @@  struct scm_cookie {
 #endif
 };
 
-int __scm_install_fd(struct file *file, int __user *ufd, unsigned int o_flags);
 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm);
 void scm_detach_fds_compat(struct msghdr *msg, struct scm_cookie *scm);
 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm);
diff --git a/net/compat.c b/net/compat.c
index 27d477fdcaa0..94f288e8dac5 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -298,7 +298,7 @@  void scm_detach_fds_compat(struct msghdr *msg, struct scm_cookie *scm)
 	int err = 0, i;
 
 	for (i = 0; i < fdmax; i++) {
-		err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
+		err = fd_install_received_user(scm->fp->fp[i], cmsg_data + i, o_flags);
 		if (err)
 			break;
 	}
diff --git a/net/core/scm.c b/net/core/scm.c
index 6151678c73ed..df190f1fdd28 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -280,36 +280,6 @@  void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_inter
 }
 EXPORT_SYMBOL(put_cmsg_scm_timestamping);
 
-int __scm_install_fd(struct file *file, int __user *ufd, unsigned int o_flags)
-{
-	struct socket *sock;
-	int new_fd;
-	int error;
-
-	error = security_file_receive(file);
-	if (error)
-		return error;
-
-	new_fd = get_unused_fd_flags(o_flags);
-	if (new_fd < 0)
-		return new_fd;
-
-	error = put_user(new_fd, ufd);
-	if (error) {
-		put_unused_fd(new_fd);
-		return error;
-	}
-
-	/* Bump the usage count and install the file. */
-	sock = sock_from_file(file, &error);
-	if (sock) {
-		sock_update_netprioidx(&sock->sk->sk_cgrp_data);
-		sock_update_classid(&sock->sk->sk_cgrp_data);
-	}
-	fd_install(new_fd, get_file(file));
-	return 0;
-}
-
 static int scm_max_fds(struct msghdr *msg)
 {
 	if (msg->msg_controllen <= sizeof(struct cmsghdr))
@@ -336,7 +306,7 @@  void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 	}
 
 	for (i = 0; i < fdmax; i++) {
-		err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
+		err = fd_install_received_user(scm->fp->fp[i], cmsg_data + i, o_flags);
 		if (err)
 			break;
 	}