miri/shims/unix/

fd.rs

//! General management of file descriptors, and support for
//! standard file descriptors (stdin/stdout/stderr).

use std::io;
use std::io::ErrorKind;

use rand::Rng;
use rustc_abi::Size;
use rustc_target::spec::Os;

use crate::shims::files::FileDescription;
use crate::shims::sig::check_min_vararg_count;
use crate::shims::unix::linux_like::epoll::EpollEvents;
use crate::shims::unix::*;
use crate::*;

#[derive(Debug, Clone, Copy, Eq, PartialEq)]
pub(crate) enum FlockOp {
    SharedLock { nonblocking: bool },
    ExclusiveLock { nonblocking: bool },
    Unlock,
}

/// Represents unix-specific file descriptions.
pub trait UnixFileDescription: FileDescription {
    /// Reads as much as possible into the given buffer `ptr` from a given offset.
    /// `len` indicates how many bytes we should try to read.
    /// `dest` is where the return value should be stored: number of bytes read, or `-1` in case of error.
    fn pread<'tcx>(
        &self,
        _communicate_allowed: bool,
        _offset: u64,
        _ptr: Pointer,
        _len: usize,
        _ecx: &mut MiriInterpCx<'tcx>,
        _finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
    ) -> InterpResult<'tcx> {
        throw_unsup_format!("cannot pread from {}", self.name());
    }

    /// Writes as much as possible from the given buffer `ptr` starting at a given offset.
    /// `ptr` is the pointer to the user supplied read buffer.
    /// `len` indicates how many bytes we should try to write.
    /// `dest` is where the return value should be stored: number of bytes written, or `-1` in case of error.
    fn pwrite<'tcx>(
        &self,
        _communicate_allowed: bool,
        _ptr: Pointer,
        _len: usize,
        _offset: u64,
        _ecx: &mut MiriInterpCx<'tcx>,
        _finish: DynMachineCallback<'tcx, Result<usize, IoError>>,
    ) -> InterpResult<'tcx> {
        throw_unsup_format!("cannot pwrite to {}", self.name());
    }

    fn flock<'tcx>(
        &self,
        _communicate_allowed: bool,
        _op: FlockOp,
    ) -> InterpResult<'tcx, io::Result<()>> {
        throw_unsup_format!("cannot flock {}", self.name());
    }

    /// Return which epoll events are currently active.
    fn epoll_active_events<'tcx>(&self) -> InterpResult<'tcx, EpollEvents> {
        throw_unsup_format!("{}: epoll does not support this file description", self.name());
    }
}

impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
    fn dup(&mut self, old_fd_num: i32) -> InterpResult<'tcx, Scalar> {
        let this = self.eval_context_mut();

        let Some(fd) = this.machine.fds.get(old_fd_num) else {
            return this.set_last_error_and_return_i32(LibcError("EBADF"));
        };
        interp_ok(Scalar::from_i32(this.machine.fds.insert(fd)))
    }

    fn dup2(&mut self, old_fd_num: i32, new_fd_num: i32) -> InterpResult<'tcx, Scalar> {
        let this = self.eval_context_mut();

        let Some(fd) = this.machine.fds.get(old_fd_num) else {
            return this.set_last_error_and_return_i32(LibcError("EBADF"));
        };
        if new_fd_num != old_fd_num {
            // Close new_fd if it is previously opened.
            // If old_fd and new_fd point to the same description, then `dup_fd` ensures we keep the underlying file description alive.
            if let Some(old_new_fd) = this.machine.fds.fds.insert(new_fd_num, fd) {
                // Ignore close error (not interpreter's) according to dup2() doc.
                old_new_fd.close_ref(this.machine.communicate(), this)?.ok();
            }
        }
        interp_ok(Scalar::from_i32(new_fd_num))
    }

    fn flock(&mut self, fd_num: i32, op: i32) -> InterpResult<'tcx, Scalar> {
        let this = self.eval_context_mut();
        let Some(fd) = this.machine.fds.get(fd_num) else {
            return this.set_last_error_and_return_i32(LibcError("EBADF"));
        };

        // We need to check that there aren't unsupported options in `op`.
        let lock_sh = this.eval_libc_i32("LOCK_SH");
        let lock_ex = this.eval_libc_i32("LOCK_EX");
        let lock_nb = this.eval_libc_i32("LOCK_NB");
        let lock_un = this.eval_libc_i32("LOCK_UN");

        use FlockOp::*;
        let parsed_op = if op == lock_sh {
            SharedLock { nonblocking: false }
        } else if op == lock_sh | lock_nb {
            SharedLock { nonblocking: true }
        } else if op == lock_ex {
            ExclusiveLock { nonblocking: false }
        } else if op == lock_ex | lock_nb {
            ExclusiveLock { nonblocking: true }
        } else if op == lock_un {
            Unlock
        } else {
            throw_unsup_format!("unsupported flags {:#x}", op);
        };

        let result = fd.as_unix(this).flock(this.machine.communicate(), parsed_op)?;
        // return `0` if flock is successful
        let result = result.map(|()| 0i32);
        interp_ok(Scalar::from_i32(this.try_unwrap_io_result(result)?))
    }

    fn fcntl(
        &mut self,
        fd_num: &OpTy<'tcx>,
        cmd: &OpTy<'tcx>,
        varargs: &[OpTy<'tcx>],
    ) -> InterpResult<'tcx, Scalar> {
        let this = self.eval_context_mut();

        let fd_num = this.read_scalar(fd_num)?.to_i32()?;
        let cmd = this.read_scalar(cmd)?.to_i32()?;

        let f_getfd = this.eval_libc_i32("F_GETFD");
        let f_dupfd = this.eval_libc_i32("F_DUPFD");
        let f_dupfd_cloexec = this.eval_libc_i32("F_DUPFD_CLOEXEC");
        let f_getfl = this.eval_libc_i32("F_GETFL");
        let f_setfl = this.eval_libc_i32("F_SETFL");

        // We only support getting the flags for a descriptor.
        match cmd {
            cmd if cmd == f_getfd => {
                // Currently this is the only flag that `F_GETFD` returns. It is OK to just return the
                // `FD_CLOEXEC` value without checking if the flag is set for the file because `std`
                // always sets this flag when opening a file. However we still need to check that the
                // file itself is open.
                if !this.machine.fds.is_fd_num(fd_num) {
                    this.set_last_error_and_return_i32(LibcError("EBADF"))
                } else {
                    interp_ok(this.eval_libc("FD_CLOEXEC"))
                }
            }
            cmd if cmd == f_dupfd || cmd == f_dupfd_cloexec => {
                // Note that we always assume the FD_CLOEXEC flag is set for every open file, in part
                // because exec() isn't supported. The F_DUPFD and F_DUPFD_CLOEXEC commands only
                // differ in whether the FD_CLOEXEC flag is pre-set on the new file descriptor,
                // thus they can share the same implementation here.
                let cmd_name = if cmd == f_dupfd {
                    "fcntl(fd, F_DUPFD, ...)"
                } else {
                    "fcntl(fd, F_DUPFD_CLOEXEC, ...)"
                };

                let [start] = check_min_vararg_count(cmd_name, varargs)?;
                let start = this.read_scalar(start)?.to_i32()?;

                if let Some(fd) = this.machine.fds.get(fd_num) {
                    interp_ok(Scalar::from_i32(this.machine.fds.insert_with_min_num(fd, start)))
                } else {
                    this.set_last_error_and_return_i32(LibcError("EBADF"))
                }
            }
            cmd if cmd == f_getfl => {
                // Check if this is a valid open file descriptor.
                let Some(fd) = this.machine.fds.get(fd_num) else {
                    return this.set_last_error_and_return_i32(LibcError("EBADF"));
                };

                fd.get_flags(this)
            }
            cmd if cmd == f_setfl => {
                // Check if this is a valid open file descriptor.
                let Some(fd) = this.machine.fds.get(fd_num) else {
                    return this.set_last_error_and_return_i32(LibcError("EBADF"));
                };

                let [flag] = check_min_vararg_count("fcntl(fd, F_SETFL, ...)", varargs)?;
                let flag = this.read_scalar(flag)?.to_i32()?;

                // Ignore flags that never get stored by SETFL.
                // "File access mode (O_RDONLY, O_WRONLY, O_RDWR) and file
                // creation flags (i.e., O_CREAT, O_EXCL, O_NOCTTY, O_TRUNC)
                // in arg are ignored."
                let ignored_flags = this.eval_libc_i32("O_RDONLY")
                    | this.eval_libc_i32("O_WRONLY")
                    | this.eval_libc_i32("O_RDWR")
                    | this.eval_libc_i32("O_CREAT")
                    | this.eval_libc_i32("O_EXCL")
                    | this.eval_libc_i32("O_NOCTTY")
                    | this.eval_libc_i32("O_TRUNC");

                fd.set_flags(flag & !ignored_flags, this)
            }
            cmd if this.tcx.sess.target.os == Os::MacOs
                && cmd == this.eval_libc_i32("F_FULLFSYNC") =>
            {
                // Reject if isolation is enabled.
                if let IsolatedOp::Reject(reject_with) = this.machine.isolated_op {
                    this.reject_in_isolation("`fcntl`", reject_with)?;
                    return this.set_last_error_and_return_i32(ErrorKind::PermissionDenied);
                }

                this.ffullsync_fd(fd_num)
            }
            cmd => {
                throw_unsup_format!("fcntl: unsupported command {cmd:#x}");
            }
        }
    }

    fn close(&mut self, fd_op: &OpTy<'tcx>) -> InterpResult<'tcx, Scalar> {
        let this = self.eval_context_mut();

        let fd_num = this.read_scalar(fd_op)?.to_i32()?;

        let Some(fd) = this.machine.fds.remove(fd_num) else {
            return this.set_last_error_and_return_i32(LibcError("EBADF"));
        };
        let result = fd.close_ref(this.machine.communicate(), this)?;
        // return `0` if close is successful
        let result = result.map(|()| 0i32);
        interp_ok(Scalar::from_i32(this.try_unwrap_io_result(result)?))
    }

    /// Read data from `fd` into buffer specified by `buf` and `count`.
    ///
    /// If `offset` is `None`, reads data from current cursor position associated with `fd`
    /// and updates cursor position on completion. Otherwise, reads from the specified offset
    /// and keeps the cursor unchanged.
    fn read(
        &mut self,
        fd_num: i32,
        buf: Pointer,
        count: u64,
        offset: Option<i128>,
        dest: &MPlaceTy<'tcx>,
    ) -> InterpResult<'tcx> {
        let this = self.eval_context_mut();

        // Isolation check is done via `FileDescription` trait.

        trace!("Reading from FD {}, size {}", fd_num, count);

        // Check that the *entire* buffer is actually valid memory.
        this.check_ptr_access(buf, Size::from_bytes(count), CheckInAllocMsg::MemoryAccess)?;

        // We cap the number of read bytes to the largest value that we are able to fit in both the
        // host's and target's `isize`. This saves us from having to handle overflows later.
        let count = count
            .min(u64::try_from(this.target_isize_max()).unwrap())
            .min(u64::try_from(isize::MAX).unwrap());
        let count = usize::try_from(count).unwrap(); // now it fits in a `usize`
        let communicate = this.machine.communicate();

        // Get the FD.
        let Some(fd) = this.machine.fds.get(fd_num) else {
            trace!("read: FD not found");
            return this.set_last_error_and_return(LibcError("EBADF"), dest);
        };

        // Handle the zero-sized case. The man page says:
        // > If count is zero, read() may detect the errors described below.  In the absence of any
        // > errors, or if read() does not check for errors, a read() with a count of 0 returns zero
        // > and has no other effects.
        if count == 0 {
            this.write_null(dest)?;
            return interp_ok(());
        }
        // Non-deterministically decide to further reduce the count, simulating a partial read (but
        // never to 0, that would indicate EOF).
        let count = if this.machine.short_fd_operations
            && fd.short_fd_operations()
            && count >= 2
            && this.machine.rng.get_mut().random()
        {
            count / 2 // since `count` is at least 2, the result is still at least 1
        } else {
            count
        };

        trace!("read: FD mapped to {fd:?}");
        // We want to read at most `count` bytes. We are sure that `count` is not negative
        // because it was a target's `usize`. Also we are sure that it's smaller than
        // `usize::MAX` because it is bounded by the host's `isize`.

        let finish = {
            let dest = dest.clone();
            callback!(
                @capture<'tcx> {
                    count: usize,
                    dest: MPlaceTy<'tcx>,
                }
                |this, result: Result<usize, IoError>| {
                    match result {
                        Ok(read_size) => {
                            assert!(read_size <= count);
                            // This must fit since `count` fits.
                            this.write_int(u64::try_from(read_size).unwrap(), &dest)
                        }
                        Err(e) => {
                            this.set_last_error_and_return(e, &dest)
                        }
                }}
            )
        };
        match offset {
            None => fd.read(communicate, buf, count, this, finish)?,
            Some(offset) => {
                let Ok(offset) = u64::try_from(offset) else {
                    return this.set_last_error_and_return(LibcError("EINVAL"), dest);
                };
                fd.as_unix(this).pread(communicate, offset, buf, count, this, finish)?
            }
        };
        interp_ok(())
    }

    fn write(
        &mut self,
        fd_num: i32,
        buf: Pointer,
        count: u64,
        offset: Option<i128>,
        dest: &MPlaceTy<'tcx>,
    ) -> InterpResult<'tcx> {
        let this = self.eval_context_mut();

        // Isolation check is done via `FileDescription` trait.

        // Check that the *entire* buffer is actually valid memory.
        this.check_ptr_access(buf, Size::from_bytes(count), CheckInAllocMsg::MemoryAccess)?;

        // We cap the number of written bytes to the largest value that we are able to fit in both the
        // host's and target's `isize`. This saves us from having to handle overflows later.
        let count = count
            .min(u64::try_from(this.target_isize_max()).unwrap())
            .min(u64::try_from(isize::MAX).unwrap());
        let count = usize::try_from(count).unwrap(); // now it fits in a `usize`
        let communicate = this.machine.communicate();

        // We temporarily dup the FD to be able to retain mutable access to `this`.
        let Some(fd) = this.machine.fds.get(fd_num) else {
            return this.set_last_error_and_return(LibcError("EBADF"), dest);
        };

        // Handle the zero-sized case. The man page says:
        // > If count is zero and fd refers to a regular file, then write() may return a failure
        // > status if one of the errors below is detected.  If no errors are detected, or error
        // > detection is not performed, 0 is returned without causing any other effect.   If  count
        // > is  zero  and  fd refers to a file other than a regular file, the results are not
        // > specified.
        if count == 0 {
            // For now let's not open the can of worms of what exactly "not specified" could mean...
            this.write_null(dest)?;
            return interp_ok(());
        }
        // Non-deterministically decide to further reduce the count, simulating a partial write.
        // We avoid reducing the write size to 0: the docs seem to be entirely fine with that,
        // but the standard library is not (https://github.com/rust-lang/rust/issues/145959).
        let count = if this.machine.short_fd_operations
            && fd.short_fd_operations()
            && count >= 2
            && this.machine.rng.get_mut().random()
        {
            count / 2
        } else {
            count
        };

        let finish = {
            let dest = dest.clone();
            callback!(
                @capture<'tcx> {
                    count: usize,
                    dest: MPlaceTy<'tcx>,
                }
                |this, result: Result<usize, IoError>| {
                    match result {
                        Ok(write_size) => {
                            assert!(write_size <= count);
                            // This must fit since `count` fits.
                            this.write_int(u64::try_from(write_size).unwrap(), &dest)
                        }
                        Err(e) => {
                            this.set_last_error_and_return(e, &dest)
                        }
                }}
            )
        };
        match offset {
            None => fd.write(communicate, buf, count, this, finish)?,
            Some(offset) => {
                let Ok(offset) = u64::try_from(offset) else {
                    return this.set_last_error_and_return(LibcError("EINVAL"), dest);
                };
                fd.as_unix(this).pwrite(communicate, buf, count, offset, this, finish)?
            }
        };
        interp_ok(())
    }
}