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Date: Tue, 28 Mar 2023 17:45:16 +0200
From: Christian Brauner <brauner@...nel.org>
To: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
Cc: davem@...emloft.net, linux-kernel@...r.kernel.org,
netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Leon Romanovsky <leon@...nel.org>,
David Ahern <dsahern@...nel.org>,
Arnd Bergmann <arnd@...db.de>,
Kees Cook <keescook@...omium.org>,
Kuniyuki Iwashima <kuniyu@...zon.com>,
Lennart Poettering <mzxreary@...inter.de>,
linux-arch@...r.kernel.org
Subject: Re: [PATCH net-next v2 2/3] net: core: add getsockopt SO_PEERPIDFD
On Wed, Mar 22, 2023 at 04:35:51PM +0100, Christian Brauner wrote:
> On Tue, Mar 21, 2023 at 07:33:41PM +0100, Alexander Mikhalitsyn wrote:
> > Add SO_PEERPIDFD which allows to get pidfd of peer socket holder pidfd.
> > This thing is direct analog of SO_PEERCRED which allows to get plain PID.
> >
> > Cc: "David S. Miller" <davem@...emloft.net>
> > Cc: Eric Dumazet <edumazet@...gle.com>
> > Cc: Jakub Kicinski <kuba@...nel.org>
> > Cc: Paolo Abeni <pabeni@...hat.com>
> > Cc: Leon Romanovsky <leon@...nel.org>
> > Cc: David Ahern <dsahern@...nel.org>
> > Cc: Arnd Bergmann <arnd@...db.de>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Christian Brauner <brauner@...nel.org>
> > Cc: Kuniyuki Iwashima <kuniyu@...zon.com>
> > Cc: Lennart Poettering <mzxreary@...inter.de>
> > Cc: linux-kernel@...r.kernel.org
> > Cc: netdev@...r.kernel.org
> > Cc: linux-arch@...r.kernel.org
> > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
> > ---
> > v2:
> > According to review comments from Kuniyuki Iwashima and Christian Brauner:
> > - use pidfd_create(..) retval as a result
> > - whitespace change
> > ---
> > arch/alpha/include/uapi/asm/socket.h | 1 +
> > arch/mips/include/uapi/asm/socket.h | 1 +
> > arch/parisc/include/uapi/asm/socket.h | 1 +
> > arch/sparc/include/uapi/asm/socket.h | 1 +
> > include/uapi/asm-generic/socket.h | 1 +
> > net/core/sock.c | 21 +++++++++++++++++++++
> > tools/include/uapi/asm-generic/socket.h | 1 +
> > 7 files changed, 27 insertions(+)
> >
> > diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
> > index ff310613ae64..e94f621903fe 100644
> > --- a/arch/alpha/include/uapi/asm/socket.h
> > +++ b/arch/alpha/include/uapi/asm/socket.h
> > @@ -138,6 +138,7 @@
> > #define SO_RCVMARK 75
> >
> > #define SO_PASSPIDFD 76
> > +#define SO_PEERPIDFD 77
> >
> > #if !defined(__KERNEL__)
> >
> > diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
> > index 762dcb80e4ec..60ebaed28a4c 100644
> > --- a/arch/mips/include/uapi/asm/socket.h
> > +++ b/arch/mips/include/uapi/asm/socket.h
> > @@ -149,6 +149,7 @@
> > #define SO_RCVMARK 75
> >
> > #define SO_PASSPIDFD 76
> > +#define SO_PEERPIDFD 77
> >
> > #if !defined(__KERNEL__)
> >
> > diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
> > index df16a3e16d64..be264c2b1a11 100644
> > --- a/arch/parisc/include/uapi/asm/socket.h
> > +++ b/arch/parisc/include/uapi/asm/socket.h
> > @@ -130,6 +130,7 @@
> > #define SO_RCVMARK 0x4049
> >
> > #define SO_PASSPIDFD 0x404A
> > +#define SO_PEERPIDFD 0x404B
> >
> > #if !defined(__KERNEL__)
> >
> > diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
> > index 6e2847804fea..682da3714686 100644
> > --- a/arch/sparc/include/uapi/asm/socket.h
> > +++ b/arch/sparc/include/uapi/asm/socket.h
> > @@ -131,6 +131,7 @@
> > #define SO_RCVMARK 0x0054
> >
> > #define SO_PASSPIDFD 0x0055
> > +#define SO_PEERPIDFD 0x0056
> >
> > #if !defined(__KERNEL__)
> >
> > diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
> > index b76169fdb80b..8ce8a39a1e5f 100644
> > --- a/include/uapi/asm-generic/socket.h
> > +++ b/include/uapi/asm-generic/socket.h
> > @@ -133,6 +133,7 @@
> > #define SO_RCVMARK 75
> >
> > #define SO_PASSPIDFD 76
> > +#define SO_PEERPIDFD 77
> >
> > #if !defined(__KERNEL__)
> >
> > diff --git a/net/core/sock.c b/net/core/sock.c
> > index 3f974246ba3e..85c269ca9d8a 100644
> > --- a/net/core/sock.c
> > +++ b/net/core/sock.c
> > @@ -1763,6 +1763,27 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
> > goto lenout;
> > }
> >
> > + case SO_PEERPIDFD:
> > + {
> > + struct pid *peer_pid;
> > + int pidfd;
> > +
> > + if (len > sizeof(pidfd))
> > + len = sizeof(pidfd);
> > +
> > + spin_lock(&sk->sk_peer_lock);
> > + peer_pid = get_pid(sk->sk_peer_pid);
> > + spin_unlock(&sk->sk_peer_lock);
> > +
> > + pidfd = pidfd_create(peer_pid, 0);
> > +
> > + put_pid(peer_pid);
> > +
> > + if (copy_to_sockptr(optval, &pidfd, len))
> > + return -EFAULT;
>
> This leaks the pidfd. We could do:
>
> if (copy_to_sockptr(optval, &pidfd, len)) {
> close_fd(pidfd);
> return -EFAULT;
> }
>
> but it's a nasty anti-pattern to install the fd in the caller's fdtable
> and then close it again. So let's avoid it if we can. Since you can only
> set one socket option per setsockopt() sycall we should be able to
> reserve an fd and pidfd_file, do the stuff that might fail, and then
> call fd_install. So that would roughly be:
>
> peer_pid = get_pid(sk->sk_peer_pid);
> pidfd_file = pidfd_file_create(peer_pid, 0, &pidfd);
> f (copy_to_sockptr(optval, &pidfd, len))
> return -EFAULT;
> goto lenout:
>
> .
> .
> .
>
> lenout:
> if (copy_to_sockptr(optlen, &len, sizeof(int)))
> return -EFAULT;
>
> // Made it safely, install pidfd now.
> fd_install(pidfd, pidfd_file)
>
> (See below for the associated api I'm going to publish independent of
> this as kernel/fork.c and fanotify both could use it.)
Sent out yesterday:
https://lore.kernel.org/lkml/20230328090026.b54a4jhccntfraey@quack3
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