fix: fix readdir libc bug

Author: akitaSummer

src/passthrough/sync_io_macos.rs

@@ -1,15 +1,13 @@
 use std::{
-    io, mem,
+    ffi::CStr,
+    io,
     os::fd::{AsRawFd, RawFd},
+    ptr,
 };
 
 use vm_memory::bitmap::BitmapSlice;
 
-use crate::{
-    api::{filesystem::DirEntry, CURRENT_DIR_CSTR, PARENT_DIR_CSTR},
-    bytes_to_cstr,
-    passthrough::util::einval,
-};
+use crate::api::filesystem::DirEntry;
 
 use super::{Handle, Inode, OffT, PassthroughFs};
 
@@ -26,95 +24,50 @@ impl<S: BitmapSlice + Send + Sync> PassthroughFs<S> {
             return Ok(());
         }
 
-        let mut buf = Vec::<u8>::with_capacity(size as usize);
         let data = self.get_dirdata(handle, inode, libc::O_RDONLY)?;
 
-        {
-            // Since we are going to work with the kernel offset, we have to acquire the file lock
-            // for both the `lseek64` and `getdents64` syscalls to ensure that no other thread
-            // changes the kernel offset while we are using it.
-            let (guard, dir) = data.get_file_mut();
-
-            // Safe because this doesn't modify any memory and we check the return value.
-            let res = unsafe { libc::lseek(dir.as_raw_fd(), offset as OffT, libc::SEEK_SET) };
-            if res < 0 {
-                return Err(io::Error::last_os_error());
-            }
-
-            // Safe because the kernel guarantees that it will only write to `buf` and we check the
-            // return value.
-            let res = unsafe {
-                libc::read(
-                    dir.as_raw_fd(),
-                    buf.as_mut_ptr() as *mut libc::c_void,
-                    size as libc::size_t,
-                )
-            };
-            if res < 0 {
-                return Err(io::Error::last_os_error());
-            }
-
-            // Safe because we trust the value returned by kernel.
-            unsafe { buf.set_len(res as usize) };
-
-            // Explicitly drop the lock so that it's not held while we fill in the fuse buffer.
-            mem::drop(guard);
+        let (_guard, dir) = data.get_file_mut();
+        if dir.metadata()?.is_dir() {
+            return Ok(());
+        }
+        // Safe because this doesn't modify any memory and we check the return value.
+        let res = unsafe { libc::lseek(dir.as_raw_fd(), offset as OffT, libc::SEEK_SET) };
+        if res < 0 {
+            return Err(io::Error::last_os_error());
         }
 
-        let mut rem = &buf[..];
-        let orig_rem_len = rem.len();
-
-        while !rem.is_empty() {
-            debug_assert!(
-                rem.len() >= mem::size_of::<libc::dirent>(),
-                "fuse: not enough space left in `rem`"
-            );
-
-            let (front, back) = rem.split_at(mem::size_of::<libc::dirent>());
+        let dir = unsafe { libc::fdopendir(dir.as_raw_fd()) };
+        loop {
+            let entry_ptr = unsafe { libc::readdir(dir) };
 
-            let dirent = unsafe { *(front.as_ptr() as *const libc::dirent) };
+            if entry_ptr.is_null() {
+                break;
+            }
 
-            let namelen = dirent.d_namlen as usize;
-            debug_assert!(
-                namelen <= back.len(),
-                "fuse: back is smaller than `namelen`"
-            );
+            let entry: libc::dirent = unsafe { ptr::read(entry_ptr) };
 
-            let name = &back[..namelen];
-            let res = if name.starts_with(CURRENT_DIR_CSTR) || name.starts_with(PARENT_DIR_CSTR) {
+            let cstr = unsafe { CStr::from_ptr(entry.d_name.as_ptr()) };
+            let name_str = cstr.to_str().expect("Failed to convert CStr to str");
+            let res = if name_str == "." || name_str == ".." {
                 Ok(1)
             } else {
-                let name = bytes_to_cstr(name)
-                    .map_err(|e| {
-                        error!("fuse: do_readdir: {:?}", e);
-                        einval()
-                    })?
-                    .to_bytes();
-
                 add_entry(
                     DirEntry {
-                        ino: dirent.d_ino,
-                        offset: dirent.d_seekoff,
-                        type_: dirent.d_type as u32,
-                        name,
+                        ino: entry.d_ino,
+                        offset: entry.d_seekoff,
+                        type_: entry.d_type as u32,
+                        name: cstr.to_bytes(),
                     },
                     data.borrow_fd().as_raw_fd(),
                 )
             };
-
-            debug_assert!(
-                rem.len() >= dirent.d_reclen as usize,
-                "fuse: rem is smaller than `d_reclen`"
-            );
-
             match res {
                 Ok(0) => break,
-                Ok(_) => rem = &rem[dirent.d_reclen as usize..],
-                Err(e) if rem.len() == orig_rem_len => return Err(e),
+                Ok(_) => continue,
                 Err(_) => return Ok(()),
             }
         }
-
+        unsafe { libc::closedir(dir) };
         Ok(())
     }
 }