fs: Don't dereference a pointer to a too-small allocation

library/std/src/sys/unix/fs.rs

@@ -491,14 +491,18 @@ impl Iterator for ReadDir {
 
                 // Only d_reclen bytes of *entry_ptr are valid, so we can't just copy the
                 // whole thing (#93384).  Instead, copy everything except the name.
+                let mut copy: dirent64 = mem::zeroed();
+                // Can't dereference entry_ptr, so use the local entry to get
+                // offsetof(struct dirent, d_name)
+                let copy_bytes = &mut copy as *mut _ as *mut u8;
+                let copy_name = &mut copy.d_name as *mut _ as *mut u8;
+                let name_offset = copy_name.offset_from(copy_bytes) as usize;
                 let entry_bytes = entry_ptr as *const u8;
-                let entry_name = ptr::addr_of!((*entry_ptr).d_name) as *const u8;
-                let name_offset = entry_name.offset_from(entry_bytes) as usize;
-                let mut entry: dirent64 = mem::zeroed();
-                ptr::copy_nonoverlapping(entry_bytes, &mut entry as *mut _ as *mut u8, name_offset);
+                let entry_name = entry_bytes.add(name_offset);
+                ptr::copy_nonoverlapping(entry_bytes, copy_bytes, name_offset);
 
                 let ret = DirEntry {
-                    entry,
+                    entry: copy,
                     // d_name is guaranteed to be null-terminated.
                     name: CStr::from_ptr(entry_name as *const _).to_owned(),
                     dir: Arc::clone(&self.inner),