Add ptrace access mode checks

kernel/src/fs/procfs/pid/task/maps.rs

@@ -4,12 +4,21 @@ use aster_util::printer::VmPrinter;
 
 use super::TidDirOps;
 use crate::{
+    events::IoEvents,
     fs::{
+        inode_handle::FileIo,
         procfs::template::{FileOps, ProcFileBuilder},
-        utils::{Inode, mkmod},
+        utils::{AccessMode, Inode, InodeIo, StatusFlags, mkmod},
     },
     prelude::*,
-    process::{Process, posix_thread::AsPosixThread},
+    process::{
+        Process,
+        posix_thread::{
+            AsPosixThread,
+            ptrace::{PtraceMode, check_may_access},
+        },
+        signal::{PollHandle, Pollable},
+    },
     vm::vmar::{VMAR_CAP_ADDR, VMAR_LOWEST_ADDR},
 };
 
@@ -28,12 +37,44 @@ impl MapsFileOps {
 }
 
 impl FileOps for MapsFileOps {
-    fn read_at(&self, offset: usize, writer: &mut VmWriter) -> Result<usize> {
+    fn read_at(&self, _offset: usize, _writer: &mut VmWriter) -> Result<usize> {
+        unreachable!("should read via opened `MapsFileHandle`")
+    }
+
+    fn write_at(&self, _offset: usize, _reader: &mut VmReader) -> Result<usize> {
+        unreachable!("should write via opened `MapsFileHandle`")
+    }
+
+    fn open(
+        &self,
+        _access_mode: AccessMode,
+        _status_flags: StatusFlags,
+    ) -> Option<Result<Box<dyn FileIo>>> {
+        let handle = check_may_access(
+            current_thread!().as_posix_thread().unwrap(),
+            self.0.main_thread().as_posix_thread().unwrap(),
+            PtraceMode::READ_FSCREDS,
+        )
+        .map(|_| Box::new(MapsFileHandle(self.0.clone())) as Box<dyn FileIo>);
+
+        Some(handle)
+    }
+}
+
+struct MapsFileHandle(Arc<Process>);
+
+impl InodeIo for MapsFileHandle {
+    fn read_at(
+        &self,
+        offset: usize,
+        writer: &mut VmWriter,
+        _status_flags: StatusFlags,
+    ) -> Result<usize> {
         let mut printer = VmPrinter::new_skip(writer, offset);
 
         let vmar_guard = self.0.lock_vmar();
         let Some(vmar) = vmar_guard.as_ref() else {
-            return_errno_with_message!(Errno::ESRCH, "the process has exited");
+            return Ok(0);
         };
 
         let current = current_thread!();
@@ -47,4 +88,30 @@ impl FileOps for MapsFileOps {
 
         Ok(printer.bytes_written())
     }
+
+    fn write_at(
+        &self,
+        _offset: usize,
+        _reader: &mut VmReader,
+        _status_flags: StatusFlags,
+    ) -> Result<usize> {
+        return_errno_with_message!(Errno::EACCES, "`/proc/[pid]/maps` is read-only");
+    }
+}
+
+impl Pollable for MapsFileHandle {
+    fn poll(&self, mask: IoEvents, _poller: Option<&mut PollHandle>) -> IoEvents {
+        let events = IoEvents::IN | IoEvents::OUT;
+        events & mask
+    }
+}
+
+impl FileIo for MapsFileHandle {
+    fn check_seekable(&self) -> Result<()> {
+        Ok(())
+    }
+
+    fn is_offset_aware(&self) -> bool {
+        true
+    }
 }

kernel/src/fs/procfs/pid/task/mem.rs

@@ -2,12 +2,21 @@
 
 use super::TidDirOps;
 use crate::{
+    events::IoEvents,
     fs::{
+        inode_handle::FileIo,
         procfs::template::{FileOps, ProcFileBuilder},
-        utils::{Inode, mkmod},
+        utils::{AccessMode, Inode, InodeIo, StatusFlags, mkmod},
     },
     prelude::*,
-    process::Process,
+    process::{
+        Process,
+        posix_thread::{
+            AsPosixThread,
+            ptrace::{PtraceMode, check_may_access},
+        },
+        signal::{PollHandle, Pollable},
+    },
 };
 
 /// Represents the inode at `/proc/[pid]/task/[tid]/mem` (and also `/proc/[pid]/mem`).
@@ -25,10 +34,49 @@ impl MemFileOps {
 }
 
 impl FileOps for MemFileOps {
-    fn read_at(&self, offset: usize, writer: &mut VmWriter) -> Result<usize> {
+    fn read_at(&self, _offset: usize, _writer: &mut VmWriter) -> Result<usize> {
+        unreachable!("should read via opened `MemFileHandle`")
+    }
+
+    fn write_at(&self, _offset: usize, _reader: &mut VmReader) -> Result<usize> {
+        unreachable!("should write via opened `MemFileHandle`")
+    }
+
+    fn open(
+        &self,
+        _access_mode: AccessMode,
+        _status_flags: StatusFlags,
+    ) -> Option<Result<Box<dyn FileIo>>> {
+        if self.0.lock_vmar().as_ref().is_none() {
+            return Some(Err(Error::with_message(
+                Errno::EACCES,
+                "the process has exited",
+            )));
+        }
+
+        let handle = check_may_access(
+            current_thread!().as_posix_thread().unwrap(),
+            self.0.main_thread().as_posix_thread().unwrap(),
+            PtraceMode::ATTACH_FSCREDS,
+        )
+        .map(|_| Box::new(MemFileHandle(self.0.clone())) as Box<dyn FileIo>);
+
+        Some(handle)
+    }
+}
+
+struct MemFileHandle(Arc<Process>);
+
+impl InodeIo for MemFileHandle {
+    fn read_at(
+        &self,
+        offset: usize,
+        writer: &mut VmWriter,
+        _status_flags: StatusFlags,
+    ) -> Result<usize> {
         let vmar_guard = self.0.lock_vmar();
         let Some(vmar) = vmar_guard.as_ref() else {
-            return_errno_with_message!(Errno::ESRCH, "the process has exited");
+            return Ok(0);
         };
         match vmar.read_remote(offset, writer) {
             Ok(bytes) => Ok(bytes),
@@ -37,10 +85,15 @@ impl FileOps for MemFileOps {
         }
     }
 
-    fn write_at(&self, offset: usize, reader: &mut VmReader) -> Result<usize> {
+    fn write_at(
+        &self,
+        offset: usize,
+        reader: &mut VmReader,
+        _status_flags: StatusFlags,
+    ) -> Result<usize> {
         let vmar_guard = self.0.lock_vmar();
         let Some(vmar) = vmar_guard.as_ref() else {
-            return_errno_with_message!(Errno::ESRCH, "the process has exited");
+            return Ok(0);
         };
         match vmar.write_remote(offset, reader) {
             Ok(bytes) => Ok(bytes),
@@ -49,3 +102,20 @@ impl FileOps for MemFileOps {
         }
     }
 }
+
+impl Pollable for MemFileHandle {
+    fn poll(&self, mask: IoEvents, _poller: Option<&mut PollHandle>) -> IoEvents {
+        let events = IoEvents::IN | IoEvents::OUT;
+        events & mask
+    }
+}
+
+impl FileIo for MemFileHandle {
+    fn check_seekable(&self) -> Result<()> {
+        Ok(())
+    }
+
+    fn is_offset_aware(&self) -> bool {
+        true
+    }
+}

kernel/src/fs/procfs/template/file.rs

@@ -6,9 +6,12 @@ use inherit_methods_macro::inherit_methods;
 
 use super::{Common, ProcFs};
 use crate::{
-    fs::utils::{
-        Extension, FileSystem, Inode, InodeIo, InodeMode, InodeType, Metadata, StatusFlags,
-        SymbolicLink,
+    fs::{
+        inode_handle::FileIo,
+        utils::{
+            AccessMode, Extension, FileSystem, Inode, InodeIo, InodeMode, InodeType, Metadata,
+            StatusFlags, SymbolicLink,
+        },
     },
     prelude::*,
     process::{Gid, Uid},
@@ -108,6 +111,14 @@ impl<F: FileOps + 'static> Inode for ProcFile<F> {
         // Seeking regular files under `/proc` with `SEEK_END` will fail.
         None
     }
+
+    fn open(
+        &self,
+        access_mode: AccessMode,
+        status_flags: StatusFlags,
+    ) -> Option<Result<Box<dyn FileIo>>> {
+        self.inner.open(access_mode, status_flags)
+    }
 }
 
 pub trait FileOps: Sync + Send {
@@ -116,4 +127,12 @@ pub trait FileOps: Sync + Send {
     fn write_at(&self, _offset: usize, _reader: &mut VmReader) -> Result<usize> {
         return_errno_with_message!(Errno::EPERM, "the file is not writable");
     }
+
+    fn open(
+        &self,
+        _access_mode: AccessMode,
+        _status_flags: StatusFlags,
+    ) -> Option<Result<Box<dyn FileIo>>> {
+        None
+    }
 }

kernel/src/process/clone.rs

@@ -391,7 +391,7 @@ fn clone_child_task(
 
         let mut thread_builder =
             PosixThreadBuilder::new(child_tid, thread_name, child_user_ctx, credentials)
-                .process(posix_thread.weak_process())
+                .process(posix_thread.weak_process().clone())
                 .sig_mask(sig_mask)
                 .file_table(child_file_table)
                 .fs(child_fs)

kernel/src/process/posix_thread/mod.rs

@@ -30,6 +30,7 @@ mod exit;
 pub mod futex;
 mod name;
 mod posix_thread_ext;
+pub mod ptrace;
 mod robust_list;
 mod thread_local;
 pub mod thread_table;
@@ -97,8 +98,8 @@ impl PosixThread {
         self.process.upgrade().unwrap()
     }
 
-    pub fn weak_process(&self) -> Weak<Process> {
-        Weak::clone(&self.process)
+    pub fn weak_process(&self) -> &Weak<Process> {
+        &self.process
     }
 
     /// Returns the thread id

kernel/src/process/posix_thread/ptrace.rs

@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use bitflags::bitflags;
+
+use crate::{
+    prelude::*,
+    process::{credentials::capabilities::CapSet, posix_thread::PosixThread},
+};
+
+/// Checks whether the current `PosixThread` may access the given target `PosixThread`
+// Reference: <https://elixir.bootlin.com/linux/v6.16.5/source/kernel/ptrace.c#L276>
+pub fn check_may_access(
+    current_pthread: &PosixThread,
+    target_pthread: &PosixThread,
+    mode: PtraceMode,
+) -> Result<()> {
+    if mode.contains(PtraceMode::FSCREDS) == mode.contains(PtraceMode::REALCREDS) {
+        return_errno_with_message!(
+            Errno::EPERM,
+            "should specify exactly one of FSCREDS and REALCREDS"
+        );
+    }
+
+    if Weak::ptr_eq(
+        current_pthread.weak_process(),
+        target_pthread.weak_process(),
+    ) {
+        return Ok(());
+    }
+
+    let cred = current_pthread.credentials();
+    let (caller_uid, caller_gid) = if mode.contains(PtraceMode::FSCREDS) {
+        (cred.fsuid(), cred.fsgid())
+    } else {
+        (cred.ruid(), cred.rgid())
+    };
+
+    let tcred = target_pthread.credentials();
+    let caller_is_same = caller_uid == tcred.euid()
+        && caller_uid == tcred.suid()
+        && caller_uid == tcred.ruid()
+        && caller_gid == tcred.egid()
+        && caller_gid == tcred.sgid()
+        && caller_gid == tcred.rgid();
+    let caller_has_cap = target_pthread
+        .process()
+        .user_ns()
+        .lock()
+        .check_cap(CapSet::SYS_PTRACE, current_pthread)
+        .is_ok();
+
+    if !caller_is_same && !caller_has_cap {
+        return_errno_with_message!(
+            Errno::EPERM,
+            "the calling process does not have the required permissions"
+        );
+    }
+
+    // TODO: Add further security checks (e.g., YAMA LSM).
+
+    Ok(())
+}
+
+bitflags! {
+    pub struct PtraceMode: u32 {
+        const READ       = 0x01;
+        const ATTACH     = 0x02;
+        const NOAUDIT    = 0x04;
+        const FSCREDS    = 0x08;
+        const REALCREDS  = 0x10;
+        const READ_FSCREDS     = Self::READ.bits()   | Self::FSCREDS.bits();
+        const READ_REALCREDS   = Self::READ.bits()   | Self::REALCREDS.bits();
+        const ATTACH_FSCREDS   = Self::ATTACH.bits() | Self::FSCREDS.bits();
+        const ATTACH_REALCREDS = Self::ATTACH.bits() | Self::REALCREDS.bits();
+    }
+}

kernel/src/syscall/pidfd_getfd.rs

@@ -3,7 +3,13 @@
 use crate::{
     fs::file_table::{FdFlags, FileDesc, get_file_fast},
     prelude::*,
-    process::{PidFile, credentials::capabilities::CapSet, posix_thread::AsPosixThread},
+    process::{
+        PidFile,
+        posix_thread::{
+            AsPosixThread,
+            ptrace::{PtraceMode, check_may_access},
+        },
+    },
     syscall::SyscallReturn,
 };
 
@@ -32,22 +38,11 @@ pub fn sys_pidfd_getfd(
         .process_opt()
         .ok_or_else(|| Error::with_message(Errno::ESRCH, "the target process has been reaped"))?;
 
-    // The calling process should have PTRACE_MODE_ATTACH_REALCREDS permissions (see ptrace(2))
-    // over the process referred to by `pidfd`.
-    // Currently, this is implemented as requiring the calling process to have the
-    // CAP_SYS_PTRACE capability, which is stricter.
-    // TODO: Implement appropriate PTRACE_MODE_ATTACH_REALCREDS permission check.
-    if process
-        .user_ns()
-        .lock()
-        .check_cap(CapSet::SYS_PTRACE, ctx.posix_thread)
-        .is_err()
-    {
-        return_errno_with_message!(
-            Errno::EPERM,
-            "the calling process does not have the required permissions"
-        );
-    }
+    check_may_access(
+        ctx.posix_thread,
+        process.main_thread().as_posix_thread().unwrap(),
+        PtraceMode::ATTACH_REALCREDS,
+    )?;
 
     let main_thread = process.main_thread();
 

test/initramfs/src/syscall/gvisor/blocklists/proc_test

@@ -12,7 +12,7 @@ ProcPid.AccessDeny
 ProcPidCwd.Subprocess
 ProcPidRoot.Subprocess
 ProcPidEnviron.MatchesEnviron
-ProcPidMem.AfterExit
+# TODO: support `ptrace`.
 ProcPidMem.DifferentUserAttached
 ProcPidFile.SubprocessRunning
 ProcPidFile.SubprocessZombie