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Error when there is an unsupported flag for opening a file #987

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Merged
merged 4 commits into from
Oct 16, 2019
Merged

Error when there is an unsupported flag for opening a file #987

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a1c6797
Error when there is an unsupported flag
pvdrz Oct 11, 2019
d73fae1
Remove F_SETFD command
pvdrz Oct 11, 2019
f76f8ce
Correct fcntl behavior
pvdrz Oct 13, 2019
2487223
Check that access mode flags only use the first two bits
pvdrz Oct 14, 2019
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66 changes: 37 additions & 29 deletions src/shims/fs.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,6 @@ use crate::*;

pub struct FileHandle {
file: File,
flag: i32,
}

pub struct FileHandler {
Expand Down Expand Up @@ -44,7 +43,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx

let mut options = OpenOptions::new();

// The first two bits of the flag correspond to the access mode of the file in linux.
// The first two bits of the flag correspond to the access mode of the file in linux. This
// is done this way because `O_RDONLY` is zero in several platforms.
let access_mode = flag & 0b11;

if access_mode == this.eval_libc_i32("O_RDONLY")? {
Expand All @@ -56,15 +56,36 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
} else {
throw_unsup_format!("Unsupported access mode {:#x}", access_mode);
}
// We need to check that there aren't unsupported options in `flag`. For this we try to
// reproduce the content of `flag` in the `mirror` variable using only the supported
// options.
let mut mirror = access_mode;

if flag & this.eval_libc_i32("O_APPEND")? != 0 {
let o_append = this.eval_libc_i32("O_APPEND")?;
if flag & o_append != 0 {
options.append(true);
mirror |= o_append;
}
if flag & this.eval_libc_i32("O_TRUNC")? != 0 {
let o_trunc = this.eval_libc_i32("O_TRUNC")?;
if flag & o_trunc != 0 {
options.truncate(true);
mirror |= o_trunc;
}
if flag & this.eval_libc_i32("O_CREAT")? != 0 {
let o_creat = this.eval_libc_i32("O_CREAT")?;
if flag & o_creat != 0 {
options.create(true);
mirror |= o_creat;
}
let o_cloexec = this.eval_libc_i32("O_CLOEXEC")?;
if flag & o_cloexec != 0 {
// We do not need to do anything for this flag because `std` already sets it.
// (Technically we do not support *not* setting this flag, but we ignore that.)
mirror |= o_cloexec;
}
// If `flag` is not equal to `mirror`, there is an unsupported option enabled in `flag`,
// then we throw an error.
if flag != mirror {
throw_unsup_format!("unsupported flags {:#x}", flag & !mirror);
}

let path_bytes = this
Expand All @@ -76,7 +97,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
let fd = options.open(path).map(|file| {
let mut fh = &mut this.machine.file_handler;
fh.low += 1;
fh.handles.insert(fh.low, FileHandle { file, flag });
fh.handles.insert(fh.low, FileHandle { file });
fh.low
});

Expand All @@ -87,7 +108,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
&mut self,
fd_op: OpTy<'tcx, Tag>,
cmd_op: OpTy<'tcx, Tag>,
arg_op: Option<OpTy<'tcx, Tag>>,
_arg1_op: Option<OpTy<'tcx, Tag>>,
) -> InterpResult<'tcx, i32> {
let this = self.eval_context_mut();

Expand All @@ -97,29 +118,16 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx

let fd = this.read_scalar(fd_op)?.to_i32()?;
let cmd = this.read_scalar(cmd_op)?.to_i32()?;

if cmd == this.eval_libc_i32("F_SETFD")? {
// This does not affect the file itself. Certain flags might require changing the file
// or the way it is accessed somehow.
let flag = this.read_scalar(arg_op.unwrap())?.to_i32()?;
// The only usage of this in stdlib at the moment is to enable the `FD_CLOEXEC` flag.
let fd_cloexec = this.eval_libc_i32("FD_CLOEXEC")?;
if let Some(FileHandle { flag: old_flag, .. }) =
this.machine.file_handler.handles.get_mut(&fd)
{
// Check that the only difference between the old flag and the current flag is
// exactly the `FD_CLOEXEC` value.
if flag ^ *old_flag == fd_cloexec {
*old_flag = flag;
} else {
throw_unsup_format!("Unsupported arg {:#x} for `F_SETFD`", flag);
}
}
Ok(0)
} else if cmd == this.eval_libc_i32("F_GETFD")? {
this.get_handle_and(fd, |handle| Ok(handle.flag))
// We only support getting the flags for a descriptor
if cmd == this.eval_libc_i32("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.
this.get_handle_and(fd, |_| Ok(0))?;
this.eval_libc_i32("FD_CLOEXEC")
} else {
throw_unsup_format!("Unsupported command {:#x}", cmd);
throw_unsup_format!("The {:#x} command is not supported for `fcntl`)", cmd);
}
}

Expand Down