dirstate-v2: Enforce data size read from the docket file

The data file may not be shorter than its size given by the docket.
It may be longer, but additional data is ignored.

Differential Revision: https://phab.mercurial-scm.org/D11089

mercurial/dirstatemap.py

@@ -637,7 +637,9 b' if rustmod is not None:'
                     data = self._opener.read(self.docket.data_filename())
                 else:
                     data = b''
-                self._rustmap = rustmod.DirstateMap.new_v2(data)
+                self._rustmap = rustmod.DirstateMap.new_v2(
+                    data, self.docket.data_size
+                )
                 parents = self.docket.parents
             else:
                 self._rustmap, parents = rustmod.DirstateMap.new_v1(

rust/hg-core/src/dirstate_tree/dirstate_map.rs

@@ -410,8 +410,15 b" impl<'on_disk> DirstateMap<'on_disk> {"
     }
 
     #[timed]
-    pub fn new_v2(on_disk: &'on_disk [u8]) -> Result<Self, DirstateError> {
-        Ok(on_disk::read(on_disk)?)
+    pub fn new_v2(
+        on_disk: &'on_disk [u8],
+        data_size: usize,
+    ) -> Result<Self, DirstateError> {
+        if let Some(data) = on_disk.get(..data_size) {
+            Ok(on_disk::read(data)?)
+        } else {
+            Err(DirstateV2ParseError.into())
+        }
     }
 
     #[timed]

rust/hg-core/src/dirstate_tree/on_disk.rs

@@ -21,7 +21,7 b' use bytes_cast::unaligned::{I32Be, I64Be'
 use bytes_cast::BytesCast;
 use format_bytes::format_bytes;
 use std::borrow::Cow;
-use std::convert::TryFrom;
+use std::convert::{TryFrom, TryInto};
 use std::time::{Duration, SystemTime, UNIX_EPOCH};
 
 /// Added at the start of `.hg/dirstate` when the "v2" format is used.
@@ -224,6 +224,11 b" impl<'on_disk> Docket<'on_disk> {"
         DirstateParents { p1, p2 }
     }
 
+    pub fn data_size(&self) -> usize {
+        // This `unwrap` could only panic on a 16-bit CPU
+        self.header.data_size.get().try_into().unwrap()
+    }
+
     pub fn data_filename(&self) -> String {
         String::from_utf8(format_bytes!(b"dirstate.{}.d", self.uuid)).unwrap()
     }

rust/hg-cpython/src/dirstate/dirstate_map.rs

@@ -83,11 +83,12 b' py_class!(pub class DirstateMap |py| {'
     @staticmethod
     def new_v2(
         on_disk: PyBytes,
+        data_size: usize,
     ) -> PyResult<PyObject> {
         let dirstate_error = |e: DirstateError| {
             PyErr::new::<exc::OSError, _>(py, format!("Dirstate error: {:?}", e))
         };
-        let inner = OwningDirstateMap::new_v2(py, on_disk)
+        let inner = OwningDirstateMap::new_v2(py, on_disk, data_size)
                 .map_err(dirstate_error)?;
         let map = Self::create_instance(py, Box::new(inner))?;
         Ok(map.into_object())

rust/hg-cpython/src/dirstate/owning.rs

@@ -48,9 +48,10 b' impl OwningDirstateMap {'
     pub fn new_v2(
         py: Python,
         on_disk: PyBytes,
+        data_size: usize,
     ) -> Result<Self, DirstateError> {
         let bytes: &'_ [u8] = on_disk.data(py);
-        let map = DirstateMap::new_v2(bytes)?;
+        let map = DirstateMap::new_v2(bytes, data_size)?;
 
         // Like in `bytes` above, this `'_` lifetime parameter borrows from
         // the bytes buffer owned by `on_disk`.

rust/rhg/src/commands/status.rs

@@ -170,11 +170,13 b' pub fn run(invocation: &crate::CliInvoca'
     let (mut dmap, parents) = if repo.has_dirstate_v2() {
         let parents;
         let dirstate_data;
+        let data_size;
         if let Some(docket_data) =
             repo.hg_vfs().read("dirstate").io_not_found_as_none()?
         {
             let docket = on_disk::read_docket(&docket_data)?;
             parents = Some(docket.parents());
+            data_size = docket.data_size();
             dirstate_data_mmap = repo
                 .hg_vfs()
                 .mmap_open(docket.data_filename())
@@ -182,9 +184,10 b' pub fn run(invocation: &crate::CliInvoca'
             dirstate_data = dirstate_data_mmap.as_deref().unwrap_or(b"");
         } else {
             parents = None;
+            data_size = 0;
             dirstate_data = b"";
         }
-        let dmap = DirstateMap::new_v2(dirstate_data)?;
+        let dmap = DirstateMap::new_v2(dirstate_data, data_size)?;
         (dmap, parents)
     } else {
         dirstate_data_mmap =