Fix pointer arithmetic around FileOperationInMirrordBinTempDir

mirrord/layer/src/common.rs

@@ -6,11 +6,8 @@ use std::{ffi::CStr, fmt::Debug, path::PathBuf};
 use libc::c_char;
 use mirrord_intproxy_protocol::{IsLayerRequest, IsLayerRequestWithResponse, MessageId};
 use mirrord_protocol::file::OpenOptionsInternal;
-<<<<<<< HEAD
-=======
 #[cfg(target_os = "macos")]
 use mirrord_sip::{MIRRORD_TEMP_BIN_DIR_CANONIC_PATHBUF, MIRRORD_TEMP_BIN_DIR_PATH_BUF};
->>>>>>> b6d57201 (Fix type errors in non-SIP crates)
 use tracing::warn;
 
 use crate::{
@@ -113,7 +110,11 @@ impl CheckedInto<PathBuf> for *const c_char {
                 // `stripped_path` is a reference to a later character in the same string as
                 // `path_str`, `stripped_path.as_ptr()` returns a pointer to a later index
                 // in the same string owned by the caller (the hooked program).
-                Detour::Bypass(Bypass::FileOperationInMirrordBinTempDir(stripped_path))
+                let prefix_len = path_str.len() - stripped_path.to_string_lossy().len();
+                Detour::Bypass(Bypass::FileOperationInMirrordBinTempDir((
+                    prefix_len,
+                    stripped_path,
+                )))
             } else {
                 Detour::Success(path_str) // strip is None, path not in temp dir.
             }

mirrord/layer/src/detour.rs

@@ -142,9 +142,11 @@ pub(crate) enum Bypass {
     CStrConversion,
 
     /// We hooked a file operation on a path in mirrord's bin directory. So do the operation
-    /// locally, but on the original path, not the one in mirrord's dir.
+    /// locally, but on the original path, not the one in mirrord's dir. The offset from the full
+    /// path to the original path is needed for pointer arithmetic, as a pointer to the String is
+    /// no longer possible.
     #[cfg(target_os = "macos")]
-    FileOperationInMirrordBinTempDir(PathBuf),
+    FileOperationInMirrordBinTempDir((usize, PathBuf)),
 
     /// File [`PathBuf`] should be ignored (used for tests).
     IgnoredFile(PathBuf),

mirrord/layer/src/exec_utils.rs

@@ -11,13 +11,9 @@ use std::{
 
 use libc::{c_char, c_int, pid_t};
 use mirrord_layer_macro::{hook_fn, hook_guard_fn};
-<<<<<<< HEAD
-use mirrord_sip::{sip_patch, SipError, MIRRORD_PATCH_DIR};
-=======
 use mirrord_sip::{
     sip_patch, SipError, MIRRORD_TEMP_BIN_DIR_CANONIC_PATHBUF, MIRRORD_TEMP_BIN_DIR_PATH_BUF,
 };
->>>>>>> b6d57201 (Fix type errors in non-SIP crates)
 use null_terminated::Nul;
 use tracing::{trace, warn};
 
@@ -322,16 +318,14 @@ pub(crate) unsafe extern "C" fn _nsget_executable_path_detour(
     let res = FN__NSGET_EXECUTABLE_PATH(path, buflen);
     if res == 0 {
         let path_buf_detour = CheckedInto::<PathBuf>::checked_into(path as *const c_char);
-        if let Bypass(FileOperationInMirrordBinTempDir(path_buf)) = path_buf_detour {
-            let later_ptr: *const i8 = path_buf.as_os_str().as_encoded_bytes().as_ptr() as _;
+        if let Bypass(FileOperationInMirrordBinTempDir((prefix_len, path_buf))) = path_buf_detour {
             // SAFETY: If we're here, the original function was passed this pointer and was
             //         successful, so this pointer must be valid.
-            let old_len = *buflen;
 
             // SAFETY:  `later_ptr` is a pointer to a later char in the same buffer.
-            let prefix_len = later_ptr.offset_from(path);
+            let later_ptr = path.wrapping_add(prefix_len);
 
-            let stripped_len = old_len - prefix_len as u32;
+            let stripped_len = path_buf.to_string_lossy().len() as u32;
 
             // SAFETY:
             // - can read `stripped_len` bytes from `path_cstring` because it's its length.
@@ -366,9 +360,9 @@ pub(crate) unsafe extern "C" fn dlopen_detour(
     // we hold the guard manually for tracing/internal code
     let guard = crate::detour::DetourGuard::new();
     let detour: Detour<PathBuf> = raw_path.checked_into();
-    let raw_path = if let Bypass(FileOperationInMirrordBinTempDir(path_buf)) = detour {
+    let raw_path = if let Bypass(FileOperationInMirrordBinTempDir((prefix_len, _))) = detour {
         trace!("dlopen called with a path inside our patch dir, switching with fixed pointer.");
-        path_buf.as_os_str().as_encoded_bytes().as_ptr() as _
+        raw_path.wrapping_add(prefix_len)
     } else {
         trace!("dlopen called on path {detour:?}.");
         raw_path

mirrord/layer/src/file/hooks.rs

@@ -62,8 +62,10 @@ fn update_ptr_from_bypass(ptr: *const c_char, bypass: Bypass) -> *const c_char {
         // inside mirrord's temp bin dir. The detour has returned us the original path of the file
         // (stripped mirrord's dir path), so now we carry out the operation locally, on the stripped
         // path.
-        Bypass::FileOperationInMirrordBinTempDir(path_buf) => {
-            path_buf.as_os_str().as_encoded_bytes().as_ptr() as _
+        Bypass::FileOperationInMirrordBinTempDir((prefix_len, path_buf)) => {
+            // add length of path to strip to ptr to obtain new pointer
+            dbg!("{:?}", path_buf.clone());
+            ptr.wrapping_add(prefix_len)
         }
         _ => ptr,
     }