Implement UNIX abstract address namespace

kernel/src/net/socket/unix/addr.rs

@@ -1,6 +1,13 @@
 // SPDX-License-Identifier: MPL-2.0
 
-use crate::{fs::path::Dentry, net::socket::util::socket_addr::SocketAddr, prelude::*};
+use keyable_arc::KeyableArc;
+
+use super::ns::{self, AbstractHandle};
+use crate::{
+    fs::{path::Dentry, utils::Inode},
+    net::socket::util::socket_addr::SocketAddr,
+    prelude::*,
+};
 
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum UnixSocketAddr {
@@ -9,10 +16,36 @@ pub enum UnixSocketAddr {
     Abstract(Arc<[u8]>),
 }
 
-#[derive(Clone, Debug)]
-pub(super) enum UnixSocketAddrBound {
-    Path(Arc<str>, Arc<Dentry>),
-    Abstract(Arc<[u8]>),
+impl UnixSocketAddr {
+    pub(super) fn bind(self) -> Result<UnixSocketAddrBound> {
+        let bound = match self {
+            Self::Unnamed => UnixSocketAddrBound::Abstract(ns::alloc_ephemeral_abstract_name()?),
+            Self::Path(path) => {
+                let dentry = ns::create_socket_file(&path)?;
+                UnixSocketAddrBound::Path(path, dentry)
+            }
+            Self::Abstract(name) => UnixSocketAddrBound::Abstract(ns::create_abstract_name(name)?),
+        };
+
+        Ok(bound)
+    }
+
+    pub(super) fn connect(&self) -> Result<UnixSocketAddrKey> {
+        let bound = match self {
+            Self::Unnamed => return_errno_with_message!(
+                Errno::EINVAL,
+                "the unnamed UNIX domain socket address is not valid for connecting"
+            ),
+            Self::Path(path) => UnixSocketAddrKey::Path(KeyableArc::from(
+                ns::lookup_socket_file(path)?.inode().clone(),
+            )),
+            Self::Abstract(name) => {
+                UnixSocketAddrKey::Abstract(KeyableArc::from(ns::lookup_abstract_name(name)?))
+            }
+        };
+
+        Ok(bound)
+    }
 }
 
 impl TryFrom<SocketAddr> for UnixSocketAddr {
@@ -26,11 +59,34 @@ impl TryFrom<SocketAddr> for UnixSocketAddr {
     }
 }
 
+#[derive(Clone, Debug)]
+pub(super) enum UnixSocketAddrBound {
+    Path(Arc<str>, Arc<Dentry>),
+    Abstract(Arc<AbstractHandle>),
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, Ord, PartialOrd, Hash)]
+pub(super) enum UnixSocketAddrKey {
+    Path(KeyableArc<dyn Inode>),
+    Abstract(KeyableArc<AbstractHandle>),
+}
+
+impl UnixSocketAddrBound {
+    pub(super) fn to_key(&self) -> UnixSocketAddrKey {
+        match self {
+            Self::Path(_, dentry) => {
+                UnixSocketAddrKey::Path(KeyableArc::from(dentry.inode().clone()))
+            }
+            Self::Abstract(handle) => UnixSocketAddrKey::Abstract(KeyableArc::from(handle.clone())),
+        }
+    }
+}
+
 impl From<UnixSocketAddrBound> for UnixSocketAddr {
     fn from(value: UnixSocketAddrBound) -> Self {
         match value {
             UnixSocketAddrBound::Path(path, _) => Self::Path(path),
-            UnixSocketAddrBound::Abstract(name) => Self::Abstract(name),
+            UnixSocketAddrBound::Abstract(name) => Self::Abstract(name.name()),
         }
     }
 }

kernel/src/net/socket/unix/mod.rs

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
 mod addr;
+mod ns;
 mod stream;
 
 pub use addr::UnixSocketAddr;

kernel/src/net/socket/unix/ns/abs.rs

@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use alloc::{collections::btree_map::Entry, format};
+
+use keyable_arc::KeyableArc;
+
+use crate::prelude::*;
+
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
+pub struct AbstractHandle(KeyableArc<[u8]>);
+
+impl AbstractHandle {
+    fn new(name: Arc<[u8]>) -> Self {
+        Self(KeyableArc::from(name))
+    }
+
+    pub fn name(&self) -> Arc<[u8]> {
+        self.0.clone().into()
+    }
+}
+
+impl Drop for AbstractHandle {
+    fn drop(&mut self) {
+        HANDLE_TABLE.remove(self.name());
+    }
+}
+
+static HANDLE_TABLE: HandleTable = HandleTable::new();
+
+struct HandleTable {
+    handles: RwLock<BTreeMap<Arc<[u8]>, Weak<AbstractHandle>>>,
+}
+
+impl HandleTable {
+    const fn new() -> Self {
+        Self {
+            handles: RwLock::new(BTreeMap::new()),
+        }
+    }
+
+    fn create(&self, name: Arc<[u8]>) -> Option<Arc<AbstractHandle>> {
+        let mut handles = self.handles.write();
+
+        let mut entry = handles.entry(name.clone());
+
+        if let Entry::Occupied(ref occupied) = entry {
+            // The handle is in use only if its strong count is greater than zero.
+            if occupied.get().strong_count() > 0 {
+                return None;
+            }
+        }
+
+        let new_handle = Arc::new(AbstractHandle::new(name));
+        let weak_handle = Arc::downgrade(&new_handle);
+
+        match entry {
+            Entry::Occupied(ref mut occupied) => {
+                occupied.insert(weak_handle);
+            }
+            Entry::Vacant(vacant) => {
+                vacant.insert(weak_handle);
+            }
+        }
+
+        Some(new_handle)
+    }
+
+    fn remove(&self, name: Arc<[u8]>) {
+        let mut handles = self.handles.write();
+
+        let Entry::Occupied(occupied) = handles.entry(name) else {
+            return;
+        };
+
+        // Due to race conditions between `AbstractHandle::drop` and `HandleTable::create`, the
+        // entry may be occupied by another handle.
+        //
+        // Therefore, before removing the entry, we must check again if the entry should be removed.
+        if occupied.get().strong_count() == 0 {
+            occupied.remove();
+        }
+    }
+
+    fn lookup(&self, name: &[u8]) -> Option<Arc<AbstractHandle>> {
+        let handles = self.handles.read();
+
+        handles.get(name).and_then(Weak::upgrade)
+    }
+
+    fn alloc_ephemeral(&self) -> Option<Arc<AbstractHandle>> {
+        // See "Autobind feature" in the man pages:
+        // <https://man7.org/linux/man-pages/man7/unix.7.html>.
+        //
+        // Note that false negatives are fine here. So we don't mind race conditions.
+        //
+        // TODO: Always starting with the first name is inefficient and leads to contention.
+        // Instead, we should generate some random names and check their availability.
+        (0..(1 << 20))
+            .map(|num| format!("{:05x}", num))
+            .map(|name| Arc::from(name.as_bytes()))
+            .filter_map(|name| self.create(name))
+            .next()
+    }
+}
+
+pub fn create_abstract_name(name: Arc<[u8]>) -> Result<Arc<AbstractHandle>> {
+    HANDLE_TABLE.create(name).ok_or_else(|| {
+        Error::with_message(Errno::EADDRINUSE, "the abstract name is already in use")
+    })
+}
+
+pub fn alloc_ephemeral_abstract_name() -> Result<Arc<AbstractHandle>> {
+    HANDLE_TABLE.alloc_ephemeral().ok_or_else(|| {
+        Error::with_message(Errno::ENOSPC, "no ephemeral abstract name is available")
+    })
+}
+
+pub fn lookup_abstract_name(name: &[u8]) -> Result<Arc<AbstractHandle>> {
+    HANDLE_TABLE
+        .lookup(name)
+        .ok_or_else(|| Error::with_message(Errno::ECONNREFUSED, "the abstract name does not exist"))
+}

kernel/src/net/socket/unix/ns/mod.rs

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: MPL-2.0
+
+pub(super) use abs::{
+    alloc_ephemeral_abstract_name, create_abstract_name, lookup_abstract_name, AbstractHandle,
+};
+pub(super) use path::{create_socket_file, lookup_socket_file};
+
+mod abs;
+mod path;

kernel/src/net/socket/unix/ns/path.rs

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use crate::{
+    fs::{
+        fs_resolver::{split_path, FsPath},
+        path::Dentry,
+        utils::{InodeMode, InodeType},
+    },
+    prelude::*,
+};
+
+pub fn lookup_socket_file(path: &str) -> Result<Arc<Dentry>> {
+    let dentry = {
+        let current = current!();
+        let fs = current.fs().read();
+        let fs_path = FsPath::try_from(path)?;
+        fs.lookup(&fs_path)?
+    };
+
+    if !dentry.mode()?.is_readable() || !dentry.mode()?.is_writable() {
+        return_errno_with_message!(Errno::EACCES, "the socket file cannot be read or written")
+    }
+
+    if dentry.type_() != InodeType::Socket {
+        return_errno_with_message!(
+            Errno::ECONNREFUSED,
+            "the specified file is not a socket file"
+        )
+    }
+
+    Ok(dentry)
+}
+
+pub fn create_socket_file(path: &str) -> Result<Arc<Dentry>> {
+    let (parent_pathname, file_name) = split_path(path);
+
+    let parent = {
+        let current = current!();
+        let fs = current.fs().read();
+        let parent_path = FsPath::try_from(parent_pathname)?;
+        fs.lookup(&parent_path)?
+    };
+
+    parent
+        .new_fs_child(
+            file_name,
+            InodeType::Socket,
+            InodeMode::S_IRUSR | InodeMode::S_IWUSR,
+        )
+        .map_err(|err| {
+            if err.error() == Errno::EEXIST {
+                Error::with_message(Errno::EADDRINUSE, "the socket file already exists")
+            } else {
+                err
+            }
+        })
+}

kernel/src/net/socket/unix/stream/init.rs

@@ -2,11 +2,6 @@
 
 use crate::{
     events::{IoEvents, Observer},
-    fs::{
-        fs_resolver::{split_path, FsPath},
-        path::Dentry,
-        utils::{InodeMode, InodeType},
-    },
     net::socket::unix::addr::{UnixSocketAddr, UnixSocketAddrBound},
     prelude::*,
     process::signal::{Pollee, Poller},
@@ -30,14 +25,7 @@ impl Init {
             return_errno_with_message!(Errno::EINVAL, "the socket is already bound");
         }
 
-        let bound_addr = match addr_to_bind {
-            UnixSocketAddr::Unnamed => todo!(),
-            UnixSocketAddr::Abstract(_) => todo!(),
-            UnixSocketAddr::Path(path) => {
-                let dentry = create_socket_file(&path)?;
-                UnixSocketAddrBound::Path(path, dentry)
-            }
-        };
+        let bound_addr = addr_to_bind.bind()?;
         self.addr = Some(bound_addr);
 
         Ok(())
@@ -67,19 +55,3 @@ impl Init {
         self.pollee.unregister_observer(observer)
     }
 }
-
-fn create_socket_file(path: &str) -> Result<Arc<Dentry>> {
-    let (parent_pathname, file_name) = split_path(path);
-    let parent = {
-        let current = current!();
-        let fs = current.fs().read();
-        let parent_path = FsPath::try_from(parent_pathname)?;
-        fs.lookup(&parent_path)?
-    };
-    let dentry = parent.new_fs_child(
-        file_name,
-        InodeType::Socket,
-        InodeMode::S_IRUSR | InodeMode::S_IWUSR,
-    )?;
-    Ok(dentry)
-}

kernel/src/net/socket/unix/stream/listener.rs

@@ -2,13 +2,14 @@
 
 use core::sync::atomic::{AtomicUsize, Ordering};
 
-use keyable_arc::KeyableWeak;
-
 use super::{connected::Connected, UnixStreamSocket};
 use crate::{
     events::{IoEvents, Observer},
-    fs::{file_handle::FileLike, path::Dentry, utils::Inode},
-    net::socket::{unix::addr::UnixSocketAddrBound, SocketAddr},
+    fs::file_handle::FileLike,
+    net::socket::{
+        unix::addr::{UnixSocketAddrBound, UnixSocketAddrKey},
+        SocketAddr,
+    },
     prelude::*,
     process::signal::{Pollee, Poller},
 };
@@ -62,15 +63,14 @@ impl Listener {
 
 impl Drop for Listener {
     fn drop(&mut self) {
-        unregister_backlog(self.backlog.addr())
+        unregister_backlog(&self.backlog.addr().to_key())
     }
 }
 
 static BACKLOG_TABLE: BacklogTable = BacklogTable::new();
 
 struct BacklogTable {
-    backlog_sockets: RwLock<BTreeMap<KeyableWeak<dyn Inode>, Arc<Backlog>>>,
-    // TODO: For linux, there is also abstract socket domain that a socket addr is not bound to an inode.
+    backlog_sockets: RwLock<BTreeMap<UnixSocketAddrKey, Arc<Backlog>>>,
 }
 
 impl BacklogTable {
@@ -81,41 +81,30 @@ impl BacklogTable {
     }
 
     fn add_backlog(&self, addr: UnixSocketAddrBound, backlog: usize) -> Option<Arc<Backlog>> {
-        let inode = {
-            let UnixSocketAddrBound::Path(_, ref dentry) = addr else {
-                todo!()
-            };
-            create_keyable_inode(dentry)
-        };
-        let new_backlog = Arc::new(Backlog::new(addr, backlog));
+        let addr_key = addr.to_key();
 
         let mut backlog_sockets = self.backlog_sockets.write();
-        if backlog_sockets.contains_key(&inode) {
+
+        if backlog_sockets.contains_key(&addr_key) {
             return None;
         }
-        backlog_sockets.insert(inode, new_backlog.clone());
+
+        let new_backlog = Arc::new(Backlog::new(addr, backlog));
+        backlog_sockets.insert(addr_key, new_backlog.clone());
 
         Some(new_backlog)
     }
 
-    fn get_backlog(&self, addr: &UnixSocketAddrBound) -> Option<Arc<Backlog>> {
-        let inode = {
-            let UnixSocketAddrBound::Path(_, dentry) = addr else {
-                todo!()
-            };
-            create_keyable_inode(dentry)
-        };
-
-        let backlog_sockets = self.backlog_sockets.read();
-        backlog_sockets.get(&inode).cloned()
+    fn get_backlog(&self, addr: &UnixSocketAddrKey) -> Option<Arc<Backlog>> {
+        self.backlog_sockets.read().get(addr).cloned()
     }
 
     fn push_incoming(
         &self,
-        server_addr: &UnixSocketAddrBound,
+        server_key: &UnixSocketAddrKey,
         client_addr: Option<UnixSocketAddrBound>,
     ) -> Result<Connected> {
-        let backlog = self.get_backlog(server_addr).ok_or_else(|| {
+        let backlog = self.get_backlog(server_key).ok_or_else(|| {
             Error::with_message(
                 Errno::ECONNREFUSED,
                 "no socket is listening at the remote address",
@@ -125,13 +114,8 @@ impl BacklogTable {
         backlog.push_incoming(client_addr)
     }
 
-    fn remove_backlog(&self, addr: &UnixSocketAddrBound) {
-        let UnixSocketAddrBound::Path(_, dentry) = addr else {
-            todo!()
-        };
-
-        let inode = create_keyable_inode(dentry);
-        self.backlog_sockets.write().remove(&inode);
+    fn remove_backlog(&self, addr_key: &UnixSocketAddrKey) {
+        self.backlog_sockets.write().remove(addr_key);
     }
 }
 
@@ -210,18 +194,13 @@ impl Backlog {
     }
 }
 
-fn create_keyable_inode(dentry: &Arc<Dentry>) -> KeyableWeak<dyn Inode> {
-    let weak_inode = Arc::downgrade(dentry.inode());
-    KeyableWeak::from(weak_inode)
-}
-
-fn unregister_backlog(addr: &UnixSocketAddrBound) {
+fn unregister_backlog(addr: &UnixSocketAddrKey) {
     BACKLOG_TABLE.remove_backlog(addr);
 }
 
 pub(super) fn push_incoming(
-    server_addr: &UnixSocketAddrBound,
+    server_key: &UnixSocketAddrKey,
     client_addr: Option<UnixSocketAddrBound>,
 ) -> Result<Connected> {
-    BACKLOG_TABLE.push_incoming(server_addr, client_addr)
+    BACKLOG_TABLE.push_incoming(server_key, client_addr)
 }

kernel/src/net/socket/unix/stream/socket.rs

@@ -11,14 +11,9 @@ use super::{
 };
 use crate::{
     events::{IoEvents, Observer},
-    fs::{
-        file_handle::FileLike,
-        fs_resolver::FsPath,
-        path::Dentry,
-        utils::{InodeType, StatusFlags},
-    },
+    fs::{file_handle::FileLike, utils::StatusFlags},
     net::socket::{
-        unix::{addr::UnixSocketAddrBound, UnixSocketAddr},
+        unix::UnixSocketAddr,
         util::{
             copy_message_from_user, copy_message_to_user, create_message_buffer,
             send_recv_flags::SendRecvFlags, socket_addr::SocketAddr, MessageHeader,
@@ -203,19 +198,7 @@ impl Socket for UnixStreamSocket {
     }
 
     fn connect(&self, socket_addr: SocketAddr) -> Result<()> {
-        let remote_addr = {
-            let unix_socket_addr = UnixSocketAddr::try_from(socket_addr)?;
-            match unix_socket_addr {
-                UnixSocketAddr::Unnamed => todo!(),
-                UnixSocketAddr::Abstract(abstract_name) => {
-                    UnixSocketAddrBound::Abstract(abstract_name)
-                }
-                UnixSocketAddr::Path(path) => {
-                    let dentry = lookup_socket_file(&path)?;
-                    UnixSocketAddrBound::Path(path, dentry)
-                }
-            }
-        };
+        let remote_addr = UnixSocketAddr::try_from(socket_addr)?.connect()?;
 
         // Note that the Linux kernel implementation locks the remote socket and checks to see if
         // it is listening first. This is different from our implementation, which locks the local
@@ -356,21 +339,3 @@ impl Socket for UnixStreamSocket {
         Ok((copied_bytes, message_header))
     }
 }
-
-fn lookup_socket_file(path: &str) -> Result<Arc<Dentry>> {
-    let dentry = {
-        let current = current!();
-        let fs = current.fs().read();
-        let fs_path = FsPath::try_from(path)?;
-        fs.lookup(&fs_path)?
-    };
-
-    if dentry.type_() != InodeType::Socket {
-        return_errno_with_message!(Errno::ENOTSOCK, "not a socket file")
-    }
-
-    if !dentry.mode()?.is_readable() || !dentry.mode()?.is_writable() {
-        return_errno_with_message!(Errno::EACCES, "the socket cannot be read or written")
-    }
-    Ok(dentry)
-}

test/apps/network/unix_err.c

@@ -3,6 +3,7 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <sys/poll.h>
+#include <fcntl.h>
 #include <unistd.h>
 #include <stddef.h>
 
@@ -233,3 +234,63 @@ FN_TEST(listen)
 	TEST_ERRNO(listen(sk_accepted, 10), EINVAL);
 }
 END_TEST()
+
+FN_TEST(ns_path)
+{
+	int fd;
+
+	fd = TEST_SUCC(creat("/tmp/.good", 0644));
+	TEST_ERRNO(bind(sk_unbound, (struct sockaddr *)&UNIX_ADDR("/tmp/.good"),
+			sizeof(struct sockaddr)),
+		   EADDRINUSE);
+	TEST_ERRNO(connect(sk_unbound,
+			   (struct sockaddr *)&UNIX_ADDR("/tmp/.good"),
+			   sizeof(struct sockaddr)),
+		   ECONNREFUSED);
+	TEST_SUCC(close(fd));
+	TEST_SUCC(unlink("/tmp/.good"));
+
+	fd = TEST_SUCC(creat("/tmp/.bad", 0000));
+	TEST_ERRNO(bind(sk_unbound, (struct sockaddr *)&UNIX_ADDR("/tmp/.bad"),
+			sizeof(struct sockaddr)),
+		   EADDRINUSE);
+	TEST_ERRNO(connect(sk_unbound,
+			   (struct sockaddr *)&UNIX_ADDR("/tmp/.bad"),
+			   sizeof(struct sockaddr)),
+		   EACCES);
+	TEST_SUCC(close(fd));
+	TEST_SUCC(unlink("/tmp/.bad"));
+}
+END_TEST()
+
+FN_TEST(ns_abs)
+{
+	int sk, sk2;
+	struct sockaddr_un addr;
+	socklen_t addrlen;
+
+	sk = TEST_SUCC(socket(PF_UNIX, SOCK_STREAM, 0));
+
+	TEST_SUCC(bind(sk, (struct sockaddr *)&UNIX_ADDR(""), PATH_OFFSET));
+	addrlen = sizeof(addr);
+	TEST_RES(getsockname(sk, (struct sockaddr *)&addr, &addrlen),
+		 addrlen == PATH_OFFSET + 6 && addr.sun_path[0] == '\0');
+
+	sk2 = TEST_SUCC(socket(PF_UNIX, SOCK_STREAM, 0));
+
+	TEST_ERRNO(bind(sk2, (struct sockaddr *)&addr, addrlen), EADDRINUSE);
+	TEST_ERRNO(connect(sk2, (struct sockaddr *)&addr, addrlen),
+		   ECONNREFUSED);
+	TEST_SUCC(listen(sk, 1));
+	TEST_SUCC(connect(sk2, (struct sockaddr *)&addr, addrlen));
+
+	TEST_SUCC(close(sk));
+	TEST_SUCC(close(sk2));
+
+	sk = TEST_SUCC(socket(PF_UNIX, SOCK_STREAM, 0));
+	TEST_ERRNO(connect(sk, (struct sockaddr *)&addr, addrlen),
+		   ECONNREFUSED);
+	TEST_SUCC(bind(sk, (struct sockaddr *)&addr, addrlen));
+	TEST_SUCC(close(sk));
+}
+END_TEST()