Implement SCM_PIDFD, a new type of CMSG type analogical to SCM_CREDENTIALS,
but it contains pidfd instead of plain pid, which allows programmers not
to care about PID reuse problem.
Idea comes from UAPI kernel group:
https://uapi-group.org/kernel-features/
Big thanks to Christian Brauner and Lennart Poettering for productive
discussions about this.
Cc: "David S. Miller" <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Paolo Abeni <[email protected]>
Cc: Leon Romanovsky <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Kuniyuki Iwashima <[email protected]>
Cc: Lennart Poettering <[email protected]>
Cc: Luca Boccassi <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Tested-by: Luca Boccassi <[email protected]>
Reviewed-by: Kuniyuki Iwashima <[email protected]>
Signed-off-by: Alexander Mikhalitsyn <[email protected]>
---
v5:
- no changes
v4:
- fixed silent fd_install if writting of CMSG to the userspace fails (pointed by Christian)
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 | 2 ++
arch/mips/include/uapi/asm/socket.h | 2 ++
arch/parisc/include/uapi/asm/socket.h | 2 ++
arch/sparc/include/uapi/asm/socket.h | 2 ++
include/linux/net.h | 1 +
include/linux/socket.h | 1 +
include/net/scm.h | 39 +++++++++++++++++++++++--
include/uapi/asm-generic/socket.h | 2 ++
net/core/sock.c | 11 +++++++
net/mptcp/sockopt.c | 1 +
net/unix/af_unix.c | 18 ++++++++----
tools/include/uapi/asm-generic/socket.h | 2 ++
12 files changed, 76 insertions(+), 7 deletions(-)
diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
index 739891b94136..ff310613ae64 100644
--- a/arch/alpha/include/uapi/asm/socket.h
+++ b/arch/alpha/include/uapi/asm/socket.h
@@ -137,6 +137,8 @@
#define SO_RCVMARK 75
+#define SO_PASSPIDFD 76
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64
diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
index 18f3d95ecfec..762dcb80e4ec 100644
--- a/arch/mips/include/uapi/asm/socket.h
+++ b/arch/mips/include/uapi/asm/socket.h
@@ -148,6 +148,8 @@
#define SO_RCVMARK 75
+#define SO_PASSPIDFD 76
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64
diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
index f486d3dfb6bb..df16a3e16d64 100644
--- a/arch/parisc/include/uapi/asm/socket.h
+++ b/arch/parisc/include/uapi/asm/socket.h
@@ -129,6 +129,8 @@
#define SO_RCVMARK 0x4049
+#define SO_PASSPIDFD 0x404A
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64
diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
index 2fda57a3ea86..6e2847804fea 100644
--- a/arch/sparc/include/uapi/asm/socket.h
+++ b/arch/sparc/include/uapi/asm/socket.h
@@ -130,6 +130,8 @@
#define SO_RCVMARK 0x0054
+#define SO_PASSPIDFD 0x0055
+
#if !defined(__KERNEL__)
diff --git a/include/linux/net.h b/include/linux/net.h
index b73ad8e3c212..c234dfbe7a30 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -43,6 +43,7 @@ struct net;
#define SOCK_PASSSEC 4
#define SOCK_SUPPORT_ZC 5
#define SOCK_CUSTOM_SOCKOPT 6
+#define SOCK_PASSPIDFD 7
#ifndef ARCH_HAS_SOCKET_TYPES
/**
diff --git a/include/linux/socket.h b/include/linux/socket.h
index 13c3a237b9c9..6bf90f251910 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -177,6 +177,7 @@ static inline size_t msg_data_left(struct msghdr *msg)
#define SCM_RIGHTS 0x01 /* rw: access rights (array of int) */
#define SCM_CREDENTIALS 0x02 /* rw: struct ucred */
#define SCM_SECURITY 0x03 /* rw: security label */
+#define SCM_PIDFD 0x04 /* ro: pidfd (int) */
struct ucred {
__u32 pid;
diff --git a/include/net/scm.h b/include/net/scm.h
index 585adc1346bd..c67f765a165b 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -120,12 +120,44 @@ static inline bool scm_has_secdata(struct socket *sock)
}
#endif /* CONFIG_SECURITY_NETWORK */
+static __inline__ void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
+{
+ struct file *pidfd_file = NULL;
+ int pidfd;
+
+ /*
+ * put_cmsg() doesn't return an error if CMSG is truncated,
+ * that's why we need to opencode these checks here.
+ */
+ if ((msg->msg_controllen <= sizeof(struct cmsghdr)) ||
+ (msg->msg_controllen - sizeof(struct cmsghdr)) < sizeof(int)) {
+ msg->msg_flags |= MSG_CTRUNC;
+ return;
+ }
+
+ WARN_ON_ONCE(!scm->pid);
+ pidfd = pidfd_prepare(scm->pid, 0, &pidfd_file);
+
+ if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) {
+ if (pidfd_file) {
+ put_unused_fd(pidfd);
+ fput(pidfd_file);
+ }
+
+ return;
+ }
+
+ if (pidfd_file)
+ fd_install(pidfd, pidfd_file);
+}
+
static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
struct scm_cookie *scm, int flags)
{
if (!msg->msg_control) {
- if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp ||
- scm_has_secdata(sock))
+ if (test_bit(SOCK_PASSCRED, &sock->flags) ||
+ test_bit(SOCK_PASSPIDFD, &sock->flags) ||
+ scm->fp || scm_has_secdata(sock))
msg->msg_flags |= MSG_CTRUNC;
scm_destroy(scm);
return;
@@ -141,6 +173,9 @@ static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(ucreds), &ucreds);
}
+ if (test_bit(SOCK_PASSPIDFD, &sock->flags))
+ scm_pidfd_recv(msg, scm);
+
scm_destroy_cred(scm);
scm_passec(sock, msg, scm);
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 638230899e98..b76169fdb80b 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -132,6 +132,8 @@
#define SO_RCVMARK 75
+#define SO_PASSPIDFD 76
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
diff --git a/net/core/sock.c b/net/core/sock.c
index 5440e67bcfe3..bb1e3f7dba79 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1246,6 +1246,13 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
clear_bit(SOCK_PASSCRED, &sock->flags);
break;
+ case SO_PASSPIDFD:
+ if (valbool)
+ set_bit(SOCK_PASSPIDFD, &sock->flags);
+ else
+ clear_bit(SOCK_PASSPIDFD, &sock->flags);
+ break;
+
case SO_TIMESTAMP_OLD:
case SO_TIMESTAMP_NEW:
case SO_TIMESTAMPNS_OLD:
@@ -1732,6 +1739,10 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
v.val = !!test_bit(SOCK_PASSCRED, &sock->flags);
break;
+ case SO_PASSPIDFD:
+ v.val = !!test_bit(SOCK_PASSPIDFD, &sock->flags);
+ break;
+
case SO_PEERCRED:
{
struct ucred peercred;
diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index d4258869ac48..e172a5848b0d 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -355,6 +355,7 @@ static int mptcp_setsockopt_sol_socket(struct mptcp_sock *msk, int optname,
case SO_BROADCAST:
case SO_BSDCOMPAT:
case SO_PASSCRED:
+ case SO_PASSPIDFD:
case SO_PASSSEC:
case SO_RXQ_OVFL:
case SO_WIFI_STATUS:
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index cc695c9f09ec..aac40106d036 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1361,7 +1361,8 @@ static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr,
if (err)
goto out;
- if (test_bit(SOCK_PASSCRED, &sock->flags) &&
+ if ((test_bit(SOCK_PASSCRED, &sock->flags) ||
+ test_bit(SOCK_PASSPIDFD, &sock->flags)) &&
!unix_sk(sk)->addr) {
err = unix_autobind(sk);
if (err)
@@ -1469,7 +1470,8 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
if (err)
goto out;
- if (test_bit(SOCK_PASSCRED, &sock->flags) && !u->addr) {
+ if ((test_bit(SOCK_PASSCRED, &sock->flags) ||
+ test_bit(SOCK_PASSPIDFD, &sock->flags)) && !u->addr) {
err = unix_autobind(sk);
if (err)
goto out;
@@ -1670,6 +1672,8 @@ static void unix_sock_inherit_flags(const struct socket *old,
{
if (test_bit(SOCK_PASSCRED, &old->flags))
set_bit(SOCK_PASSCRED, &new->flags);
+ if (test_bit(SOCK_PASSPIDFD, &old->flags))
+ set_bit(SOCK_PASSPIDFD, &new->flags);
if (test_bit(SOCK_PASSSEC, &old->flags))
set_bit(SOCK_PASSSEC, &new->flags);
}
@@ -1819,8 +1823,10 @@ static bool unix_passcred_enabled(const struct socket *sock,
const struct sock *other)
{
return test_bit(SOCK_PASSCRED, &sock->flags) ||
+ test_bit(SOCK_PASSPIDFD, &sock->flags) ||
!other->sk_socket ||
- test_bit(SOCK_PASSCRED, &other->sk_socket->flags);
+ test_bit(SOCK_PASSCRED, &other->sk_socket->flags) ||
+ test_bit(SOCK_PASSPIDFD, &other->sk_socket->flags);
}
/*
@@ -1922,7 +1928,8 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
goto out;
}
- if (test_bit(SOCK_PASSCRED, &sock->flags) && !u->addr) {
+ if ((test_bit(SOCK_PASSCRED, &sock->flags) ||
+ test_bit(SOCK_PASSPIDFD, &sock->flags)) && !u->addr) {
err = unix_autobind(sk);
if (err)
goto out;
@@ -2824,7 +2831,8 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
/* Never glue messages from different writers */
if (!unix_skb_scm_eq(skb, &scm))
break;
- } else if (test_bit(SOCK_PASSCRED, &sock->flags)) {
+ } else if (test_bit(SOCK_PASSCRED, &sock->flags) ||
+ test_bit(SOCK_PASSPIDFD, &sock->flags)) {
/* Copy credentials */
scm_set_cred(&scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
unix_set_secdata(&scm, skb);
diff --git a/tools/include/uapi/asm-generic/socket.h b/tools/include/uapi/asm-generic/socket.h
index 8756df13be50..fbbc4bf53ee3 100644
--- a/tools/include/uapi/asm-generic/socket.h
+++ b/tools/include/uapi/asm-generic/socket.h
@@ -121,6 +121,8 @@
#define SO_RCVMARK 75
+#define SO_PASSPIDFD 76
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
--
2.34.1
On Wed, May 17, 2023 at 01:33:49PM +0200, Alexander Mikhalitsyn wrote:
> Implement SCM_PIDFD, a new type of CMSG type analogical to SCM_CREDENTIALS,
> but it contains pidfd instead of plain pid, which allows programmers not
> to care about PID reuse problem.
>
> Idea comes from UAPI kernel group:
> https://uapi-group.org/kernel-features/
>
> Big thanks to Christian Brauner and Lennart Poettering for productive
> discussions about this.
>
> Cc: "David S. Miller" <[email protected]>
> Cc: Eric Dumazet <[email protected]>
> Cc: Jakub Kicinski <[email protected]>
> Cc: Paolo Abeni <[email protected]>
> Cc: Leon Romanovsky <[email protected]>
> Cc: David Ahern <[email protected]>
> Cc: Arnd Bergmann <[email protected]>
> Cc: Kees Cook <[email protected]>
> Cc: Christian Brauner <[email protected]>
> Cc: Kuniyuki Iwashima <[email protected]>
> Cc: Lennart Poettering <[email protected]>
> Cc: Luca Boccassi <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Tested-by: Luca Boccassi <[email protected]>
> Reviewed-by: Kuniyuki Iwashima <[email protected]>
> Signed-off-by: Alexander Mikhalitsyn <[email protected]>
> ---
> v5:
> - no changes
Looks good to me,
Reviewed-by: Christian Brauner <[email protected]>
Hi Alexander,
kernel test robot noticed the following build errors:
[auto build test ERROR on net-next/main]
url: https://github.com/intel-lab-lkp/linux/commits/Alexander-Mikhalitsyn/scm-add-SO_PASSPIDFD-and-SCM_PIDFD/20230517-193620
base: net-next/main
patch link: https://lore.kernel.org/r/20230517113351.308771-2-aleksandr.mikhalitsyn%40canonical.com
patch subject: [PATCH net-next v5 1/3] scm: add SO_PASSPIDFD and SCM_PIDFD
config: powerpc-randconfig-s043-20230517
compiler: powerpc-linux-gcc (GCC) 12.1.0
reproduce:
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# apt-get install sparse
# sparse version: v0.6.4-39-gce1a6720-dirty
# https://github.com/intel-lab-lkp/linux/commit/969a57c99c9d50bfebd0908f5157870b36c271c7
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Alexander-Mikhalitsyn/scm-add-SO_PASSPIDFD-and-SCM_PIDFD/20230517-193620
git checkout 969a57c99c9d50bfebd0908f5157870b36c271c7
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=powerpc olddefconfig
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=powerpc SHELL=/bin/bash
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
All errors (new ones prefixed by >>, old ones prefixed by <<):
>> ERROR: modpost: "pidfd_prepare" [net/unix/unix.ko] undefined!
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
On Sat, May 20, 2023 at 10:11:36PM +0800, kernel test robot wrote:
> Hi Alexander,
>
> kernel test robot noticed the following build errors:
>
> [auto build test ERROR on net-next/main]
>
> url: https://github.com/intel-lab-lkp/linux/commits/Alexander-Mikhalitsyn/scm-add-SO_PASSPIDFD-and-SCM_PIDFD/20230517-193620
> base: net-next/main
> patch link: https://lore.kernel.org/r/20230517113351.308771-2-aleksandr.mikhalitsyn%40canonical.com
> patch subject: [PATCH net-next v5 1/3] scm: add SO_PASSPIDFD and SCM_PIDFD
> config: powerpc-randconfig-s043-20230517
> compiler: powerpc-linux-gcc (GCC) 12.1.0
> reproduce:
> wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> chmod +x ~/bin/make.cross
> # apt-get install sparse
> # sparse version: v0.6.4-39-gce1a6720-dirty
> # https://github.com/intel-lab-lkp/linux/commit/969a57c99c9d50bfebd0908f5157870b36c271c7
> git remote add linux-review https://github.com/intel-lab-lkp/linux
> git fetch --no-tags linux-review Alexander-Mikhalitsyn/scm-add-SO_PASSPIDFD-and-SCM_PIDFD/20230517-193620
> git checkout 969a57c99c9d50bfebd0908f5157870b36c271c7
> # save the config file
> mkdir build_dir && cp config build_dir/.config
> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=powerpc olddefconfig
> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=powerpc SHELL=/bin/bash
>
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <[email protected]>
> | Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
>
> All errors (new ones prefixed by >>, old ones prefixed by <<):
>
> >> ERROR: modpost: "pidfd_prepare" [net/unix/unix.ko] undefined!
TLI, that AF_UNIX can be a kernel module...
I'm really not excited in exposing pidfd_prepare() to non-core kernel
code. Would it be possible to please simply refuse SO_PEERPIDFD and
SCM_PIDFD if AF_UNIX is compiled as a module? I feel that this must be
super rare because it risks breaking even simplistic userspace.
On Mon, May 22, 2023 at 11:47:08AM +0200, Christian Brauner wrote:
> On Sat, May 20, 2023 at 10:11:36PM +0800, kernel test robot wrote:
> > Hi Alexander,
> >
> > kernel test robot noticed the following build errors:
> >
> > [auto build test ERROR on net-next/main]
> >
> > url: https://github.com/intel-lab-lkp/linux/commits/Alexander-Mikhalitsyn/scm-add-SO_PASSPIDFD-and-SCM_PIDFD/20230517-193620
> > base: net-next/main
> > patch link: https://lore.kernel.org/r/20230517113351.308771-2-aleksandr.mikhalitsyn%40canonical.com
> > patch subject: [PATCH net-next v5 1/3] scm: add SO_PASSPIDFD and SCM_PIDFD
> > config: powerpc-randconfig-s043-20230517
> > compiler: powerpc-linux-gcc (GCC) 12.1.0
> > reproduce:
> > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > chmod +x ~/bin/make.cross
> > # apt-get install sparse
> > # sparse version: v0.6.4-39-gce1a6720-dirty
> > # https://github.com/intel-lab-lkp/linux/commit/969a57c99c9d50bfebd0908f5157870b36c271c7
> > git remote add linux-review https://github.com/intel-lab-lkp/linux
> > git fetch --no-tags linux-review Alexander-Mikhalitsyn/scm-add-SO_PASSPIDFD-and-SCM_PIDFD/20230517-193620
> > git checkout 969a57c99c9d50bfebd0908f5157870b36c271c7
> > # save the config file
> > mkdir build_dir && cp config build_dir/.config
> > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=powerpc olddefconfig
> > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=powerpc SHELL=/bin/bash
> >
> > If you fix the issue, kindly add following tag where applicable
> > | Reported-by: kernel test robot <[email protected]>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
> >
> > All errors (new ones prefixed by >>, old ones prefixed by <<):
> >
> > >> ERROR: modpost: "pidfd_prepare" [net/unix/unix.ko] undefined!
>
> TLI, that AF_UNIX can be a kernel module...
> I'm really not excited in exposing pidfd_prepare() to non-core kernel
> code. Would it be possible to please simply refuse SO_PEERPIDFD and
> SCM_PIDFD if AF_UNIX is compiled as a module? I feel that this must be
> super rare because it risks breaking even simplistic userspace.
It occurs to me that it may be simpler to not allow AF_UNIX to be a module.
But perhaps that breaks something for someone...
On Mon, 22 May 2023 at 21:13, Jakub Kicinski <[email protected]> wrote:
>
> On Mon, 22 May 2023 15:19:17 +0200 Simon Horman wrote:
> > > TLI, that AF_UNIX can be a kernel module...
> > > I'm really not excited in exposing pidfd_prepare() to non-core kernel
> > > code. Would it be possible to please simply refuse SO_PEERPIDFD and
> > > SCM_PIDFD if AF_UNIX is compiled as a module? I feel that this must be
> > > super rare because it risks breaking even simplistic userspace.
> >
> > It occurs to me that it may be simpler to not allow AF_UNIX to be a module.
> > But perhaps that breaks something for someone...
>
> Both of the two options (disable the feature with unix=m, make unix
> bool) could lead to breakage, I reckon at least the latter makes
> the breakage more obvious? So not allowing AF_UNIX as a module
> gets my vote as well.
>
> A mechanism of exporting symbols for core/internal use only would
> find a lot of use in networking :(
We are eagerly waiting for this UAPI to be merged so that we can use
it in userspace (systemd/dbus/dbus-broker/polkitd), so I would much
rather if such impactful changes could be delayed until after, as
there is bound to be somebody complaining about such a change, and
making this dependent on that will likely jeopardize landing this
series.
v6 adds fixed this so that's disabled if AF_UNIX is not built-in via
'IS_BUILTIN', and that seems like a perfect starting point to me, if
AF_UNIX can be made non-optional or non-module it can be refactored
easily later.
Kind regards,
Luca Boccassi
On Mon, 22 May 2023 15:19:17 +0200 Simon Horman wrote:
> > TLI, that AF_UNIX can be a kernel module...
> > I'm really not excited in exposing pidfd_prepare() to non-core kernel
> > code. Would it be possible to please simply refuse SO_PEERPIDFD and
> > SCM_PIDFD if AF_UNIX is compiled as a module? I feel that this must be
> > super rare because it risks breaking even simplistic userspace.
>
> It occurs to me that it may be simpler to not allow AF_UNIX to be a module.
> But perhaps that breaks something for someone...
Both of the two options (disable the feature with unix=m, make unix
bool) could lead to breakage, I reckon at least the latter makes
the breakage more obvious? So not allowing AF_UNIX as a module
gets my vote as well.
A mechanism of exporting symbols for core/internal use only would
find a lot of use in networking :(
On Mon, May 22, 2023 at 09:17:46PM +0100, Luca Boccassi wrote:
> On Mon, 22 May 2023 at 21:13, Jakub Kicinski <[email protected]> wrote:
> >
> > On Mon, 22 May 2023 15:19:17 +0200 Simon Horman wrote:
> > > > TLI, that AF_UNIX can be a kernel module...
> > > > I'm really not excited in exposing pidfd_prepare() to non-core kernel
> > > > code. Would it be possible to please simply refuse SO_PEERPIDFD and
> > > > SCM_PIDFD if AF_UNIX is compiled as a module? I feel that this must be
> > > > super rare because it risks breaking even simplistic userspace.
> > >
> > > It occurs to me that it may be simpler to not allow AF_UNIX to be a module.
> > > But perhaps that breaks something for someone...
> >
> > Both of the two options (disable the feature with unix=m, make unix
> > bool) could lead to breakage, I reckon at least the latter makes
> > the breakage more obvious? So not allowing AF_UNIX as a module
> > gets my vote as well.
> >
> > A mechanism of exporting symbols for core/internal use only would
> > find a lot of use in networking :(
>
> We are eagerly waiting for this UAPI to be merged so that we can use
> it in userspace (systemd/dbus/dbus-broker/polkitd), so I would much
> rather if such impactful changes could be delayed until after, as
> there is bound to be somebody complaining about such a change, and
> making this dependent on that will likely jeopardize landing this
> series.
> v6 adds fixed this so that's disabled if AF_UNIX is not built-in via
> 'IS_BUILTIN', and that seems like a perfect starting point to me, if
> AF_UNIX can be made non-optional or non-module it can be refactored
> easily later.
No objections from my side, as long as we're not exposing symbols
that we'd rather not have exposed, or otherwise creating new problems.
Let's resolve the AF_UNIX question at some point.