Handle overflow errors in Bytes -> Pages conversion

wasmerio · Dec 10, 2020 · afc879a · afc879a
1 parent df3a211
commit afc879a
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Showing 3 changed files with 46 additions and 5 deletions.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -12,6 +12,7 @@
 * [#1867](https://github.com/wasmerio/wasmer/pull/1867) Added `Metering::get_remaining_points` and `Metering::set_remaining_points` 
 * [#1881](https://github.com/wasmerio/wasmer/pull/1881) Added `UnsupportedTarget` error to `CompileError`
 * [#1908](https://github.com/wasmerio/wasmer/pull/1908) Implemented `TryFrom<Value<T>>` for `i32`/`u32`/`i64`/`u64`/`f32`/`f64`
+* [#1914](https://github.com/wasmerio/wasmer/pull/1914) Implemented `TryFrom<Bytes> for Pages` instead of `From<Bytes> for Pages` to properly handle overflow errors
 
 ### Changed
 

diff --git a/lib/vm/src/memory.rs b/lib/vm/src/memory.rs
@@ -318,7 +318,7 @@ impl Memory for LinearMemory {
         unsafe {
             let md_ptr = self.get_vm_memory_definition();
             let md = md_ptr.as_ref();
-            Bytes::from(md.current_length).into()
+            Bytes::from(md.current_length).try_into().unwrap()
         }
     }
 
@@ -376,7 +376,7 @@ impl Memory for LinearMemory {
                     .checked_add(guard_bytes)
                     .ok_or_else(|| MemoryError::CouldNotGrow {
                         current: new_pages,
-                        attempted_delta: Bytes(guard_bytes).into(),
+                        attempted_delta: Bytes(guard_bytes).try_into().unwrap(),
                     })?;
 
             let mut new_mmap =

diff --git a/lib/wasmer-types/src/units.rs b/lib/wasmer-types/src/units.rs
@@ -1,3 +1,4 @@
+use crate::lib::std::convert::TryFrom;
 use crate::lib::std::fmt;
 use crate::lib::std::ops::{Add, Sub};
 #[cfg(feature = "enable-serde")]
@@ -108,9 +109,16 @@ where
     }
 }
 
-impl From<Bytes> for Pages {
-    fn from(bytes: Bytes) -> Self {
-        Self((bytes.0 / WASM_PAGE_SIZE) as u32)
+const PAGES_EXCEED_UINT32: &'static str = "Number of pages exceeds uint32 range";
+
+impl TryFrom<Bytes> for Pages {
+    type Error = &'static str;
+
+    fn try_from(bytes: Bytes) -> Result<Self, Self::Error> {
+        let pages: u32 = (bytes.0 / WASM_PAGE_SIZE)
+            .try_into()
+            .or(Err(PAGES_EXCEED_UINT32))?;
+        Ok(Self(pages))
     }
 }
 
@@ -133,3 +141,35 @@ where
         Self(self.0 + rhs.into().0)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn convert_bytes_to_pages() {
+        // rounds down
+        let pages = Pages::try_from(Bytes(0)).unwrap();
+        assert_eq!(pages, Pages(0));
+        let pages = Pages::try_from(Bytes(1)).unwrap();
+        assert_eq!(pages, Pages(0));
+        let pages = Pages::try_from(Bytes(WASM_PAGE_SIZE - 1)).unwrap();
+        assert_eq!(pages, Pages(0));
+        let pages = Pages::try_from(Bytes(WASM_PAGE_SIZE)).unwrap();
+        assert_eq!(pages, Pages(1));
+        let pages = Pages::try_from(Bytes(WASM_PAGE_SIZE + 1)).unwrap();
+        assert_eq!(pages, Pages(1));
+        let pages = Pages::try_from(Bytes(28 * WASM_PAGE_SIZE + 42)).unwrap();
+        assert_eq!(pages, Pages(28));
+        let pages = Pages::try_from(Bytes((u32::MAX as usize) * WASM_PAGE_SIZE)).unwrap();
+        assert_eq!(pages, Pages(u32::MAX));
+        let pages = Pages::try_from(Bytes((u32::MAX as usize) * WASM_PAGE_SIZE + 1)).unwrap();
+        assert_eq!(pages, Pages(u32::MAX));
+
+        // Errors when page count cannot be represented as u32
+        let result = Pages::try_from(Bytes((u32::MAX as usize + 1) * WASM_PAGE_SIZE));
+        assert_eq!(result.unwrap_err(), "Number of pages exceeds uint32 range");
+        let result = Pages::try_from(Bytes(usize::MAX));
+        assert_eq!(result.unwrap_err(), "Number of pages exceeds uint32 range");
+    }
+}