fix(vfs): 修复 pread64 系统调用的兼容性和错误处理 #1398

kaleidoscope416 · 2025-11-21T09:49:17Z

验证 offset 参数：当偏移量为负数或发生溢出时返回 EINVAL。
验证用户缓冲区：使用 new_checked 确保内存已映射，从而正确返回 EFAULT。
检查文件类型：对不可定位的文件（如管道、Socket）返回 ESPIPE。
修复 File::readable() 中的权限检查：
- 对 O_PATH 文件描述符返回 EBADF。
- 对只写模式（Write-only）打开的文件返回 EBADF 而不是 EPERM。
修复了 gVisor pread64 测试集中的多个失败项，包括 BadBuffer、CantReadSocketPair、WriteOnlyNotReadable、Pread64WithOpath、BadOffset 和 Overflow。

Note

Validate pread64 offset for overflow/negativity, reject non-seekable fds with ESPIPE, switch to new_checked/user_accessible_len for robust user buffer checks, and enable gVisor pread64 tests (blocklist Overflow).

Syscall: pread64 (kernel/src/filesystem/vfs/syscall/sys_pread64.rs)
- Validate offset and offset + len (cap at i64::MAX, return EINVAL on overflow/negative).
- Use UserBufferWriter::new_checked to return EFAULT for unmapped/insufficiently mapped buffers.
- Reject non-seekable types (Pipe, Socket, CharDevice) with ESPIPE before read.
User access (kernel/src/syscall/user_access.rs)
- Replace page-table boolean checks with user_accessible_len in new_checked and convert_with_offset_checked for readers/writers; return EFAULT if accessible range < requested.
Tests
- Add gVisor blocklist for pread64_test: Pread64Test.Overflow.
- Whitelist pread64_test in user/apps/tests/syscall/gvisor/whitelist.txt.

^{Written by Cursor Bugbot for commit 667c09c. This will update automatically on new commits. Configure here.}

- 验证 `offset` 参数：当偏移量为负数或发生溢出时返回 `EINVAL`。 - 验证用户缓冲区：使用 `new_checked` 确保内存已映射，从而正确返回 `EFAULT`。 - 检查文件类型：对不可定位的文件（如管道、Socket）返回 `ESPIPE`。 - 修复 `File::readable()` 中的权限检查： - 对 `O_PATH` 文件描述符返回 `EBADF`。 - 对只写模式（Write-only）打开的文件返回 `EBADF` 而不是 `EPERM`。 - 修复了 gVisor `pread64` 测试集中的多个失败项，包括 `BadBuffer`、`CantReadSocketPair`、`WriteOnlyNotReadable`、`Pread64WithOpath`、`BadOffset` 和 `Overflow`。

Copilot

Pull Request Overview

This pull request enhances the pread64 system call implementation to fix compatibility issues with the gVisor test suite by adding comprehensive validation and error handling. The changes improve POSIX compliance by properly validating parameters and file descriptor states before performing read operations.

Key Changes

Added offset validation to reject negative values and detect arithmetic overflow
Switched from UserBufferWriter::new to new_checked for proper EFAULT handling on unmapped memory
Added file type checking to return ESPIPE for non-seekable file types (pipes and sockets)
Fixed File::readable() permission checks to properly handle O_PATH file descriptors and return EBADF (instead of EPERM) for write-only files using the accmode() method

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
kernel/src/filesystem/vfs/syscall/sys_pread64.rs	Added parameter validation (offset bounds, overflow checks), buffer verification, and file type checking for non-seekable files
kernel/src/filesystem/vfs/file.rs	Improved `readable()` method to check O_PATH flag and use proper access mode extraction with correct EBADF error code for write-only files

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Copilot · 2025-11-21T09:52:53Z

kernel/src/filesystem/vfs/syscall/sys_pread64.rs


+        // 检查是否是管道/Socket (ESPIPE)
+        let md = file.metadata()?;
+        if md.file_type == FileType::Pipe || md.file_type == FileType::Socket {


Incomplete file type check for non-seekable files: The check should also include FileType::CharDevice to be consistent with lseek() at file.rs:364, which returns ESPIPE for both Pipe and CharDevice. Character devices like terminals are non-seekable and should fail pread64 with ESPIPE.

Should be: if md.file_type == FileType::Pipe || md.file_type == FileType::Socket || md.file_type == FileType::CharDevice

Suggested change

if md.file_type == FileType::Pipe || md.file_type == FileType::Socket {

if md.file_type == FileType::Pipe || md.file_type == FileType::Socket || md.file_type == FileType::CharDevice {

Copilot · 2025-11-21T09:52:54Z

kernel/src/filesystem/vfs/syscall/sys_pread64.rs

+        // 检查offset + len是否溢出
+        if offset.checked_add(len).is_none() || offset > i64::MAX as usize {


Incomplete overflow check: The validation should also check if offset + len exceeds i64::MAX, not just offset alone. If offset is valid but offset + len > i64::MAX, this should also return EINVAL.

Consider: if offset.checked_add(len).map_or(true, |sum| sum > i64::MAX as usize) || offset > i64::MAX as usize

Or split into clearer logic:

let end_pos = offset.checked_add(len).ok_or(SystemError::EINVAL)?; if offset > i64::MAX as usize || end_pos > i64::MAX as usize { return Err(SystemError::EINVAL); }

Suggested change

// 检查offset + len是否溢出

if offset.checked_add(len).is_none() || offset > i64::MAX as usize {

// 检查offset + len是否溢出，并且两者都不能超过i64::MAX

let end_pos = offset.checked_add(len).ok_or(SystemError::EINVAL)?;

if offset > i64::MAX as usize || end_pos > i64::MAX as usize {

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Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

kernel/src/filesystem/vfs/file.rs:437

Inconsistency with readable(): the writeable() method still returns EPERM for read-only files, while readable() now returns EBADF for write-only files. For consistency with POSIX standards and the pattern established in readable(), this should also return EBADF instead of EPERM. Additionally, line 436 should use mode.accmode() == FileMode::O_RDONLY.bits() instead of direct comparison, similar to line 418.

        if mode == FileMode::O_RDONLY {
            return Err(SystemError::EPERM);

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kernel/src/filesystem/vfs/syscall/sys_pread64.rs

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Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

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Copilot · 2025-11-24T07:59:54Z

kernel/src/filesystem/vfs/file.rs

+        let mode = *self.mode.read();
+
+        // 检查是否是O_PATH文件描述符
+        if mode == FileMode::O_WRONLY || mode.contains(FileMode::O_PATH) {


Missing space after || operator. The condition should be mode == FileMode::O_WRONLY || mode.contains(FileMode::O_PATH) for consistency with Rust formatting conventions.

Copilot · 2025-11-24T07:59:55Z

kernel/src/filesystem/vfs/syscall/sys_pread64.rs

+        // 检查offset是否为负数
+        if (offset as isize) < 0 {
+            return Err(SystemError::EINVAL);
+        }
+


The check (offset as isize) < 0 is redundant with the check on line 47 offset > i64::MAX as usize. Both conditions check if offset >= 2^63 (on 64-bit systems). The first check interprets the value as signed and checks if the sign bit is set, while the second explicitly compares against i64::MAX. Consider removing the first check to avoid duplication and improve code clarity.

Suggested change

// 检查offset是否为负数

if (offset as isize) < 0 {

return Err(SystemError::EINVAL);

}

Copilot · 2025-11-24T07:59:55Z

user/apps/tests/syscall/gvisor/blocklists/pread64_test

@@ -0,0 +1,4 @@
+# SYS_MEMFD_CREATE未实现
+Pread64Test.Overflow


According to the PR description, the Overflow test case should now be fixed (listed among the fixed test cases). However, it's still present in the blocklist. If the test is indeed fixed, it should be removed from this blocklist. If it still needs to be blocked for a different reason (SYS_MEMFD_CREATE not implemented), the comment and PR description should be clarified to explain that only partial fixes were made.

Suggested change

Pread64Test.Overflow

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Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

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Copilot · 2025-11-24T08:22:58Z

kernel/src/filesystem/vfs/file.rs

+        let mode = *self.mode.read();
+
+        // 检查是否是O_PATH文件描述符
+        if mode == FileMode::O_WRONLY || mode.contains(FileMode::O_PATH) {


The check mode == FileMode::O_WRONLY is incorrect because it only matches when the mode is exactly O_WRONLY (0o1) with no other flags set. A file opened with O_WRONLY | O_NONBLOCK (0o4001) would incorrectly pass this check as readable.

The correct check should use the access mode bits:

if mode.accmode() == FileMode::O_WRONLY.bits() || mode.contains(FileMode::O_PATH) { return Err(SystemError::EBADF); }

This ensures we properly check only the access mode portion of the flags (lowest 2 bits), not the entire flag value.

Suggested change

if mode == FileMode::O_WRONLY || mode.contains(FileMode::O_PATH) {

if mode.accmode() == FileMode::O_WRONLY.bits() || mode.contains(FileMode::O_PATH) {

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fslongjin · 2025-11-25T16:27:21Z

kernel/src/filesystem/vfs/syscall/sys_pread64.rs

+        }
+
+        let mut user_buffer_writer =
+            UserBufferWriter::new_checked(buf_vaddr, len, frame.is_from_user())?;


要求用户缓冲区已经映射应该是不对的。可能是pagefault延迟映射。应该是使用protected的那个，校验vma

kernel/src/filesystem/vfs/syscall/sys_pread64.rs

…_pread64

…ser access modules - Updated SysPread64Handle to use new_checked for user buffer writing. - Enhanced user access validation by replacing direct checks with user_accessible_len in UserBufferReader and UserBufferWriter. Signed-off-by: longjin <[email protected]>

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kernel/src/filesystem/vfs/syscall/sys_pread64.rs

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删去冗余的负数判断

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增加注释

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Merge remote-tracking branch 'origin/master' into jiangruizhi-fix/sys…

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…_pread64

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禁用preadv的不稳定测试

cbad321

	if md.file_type == FileType::Pipe \|\| md.file_type == FileType::Socket {
	if md.file_type == FileType::Pipe \|\| md.file_type == FileType::Socket \|\| md.file_type == FileType::CharDevice {

		// 检查offset + len是否溢出
		if offset.checked_add(len).is_none() \|\| offset > i64::MAX as usize {

-        // 检查offset + len是否溢出
-        if offset.checked_add(len).is_none() || offset > i64::MAX as usize {
+        // 检查offset + len是否溢出，并且两者都不能超过i64::MAX
+        let end_pos = offset.checked_add(len).ok_or(SystemError::EINVAL)?;
+        if offset > i64::MAX as usize || end_pos > i64::MAX as usize {

		@@ -0,0 +1,4 @@
		# SYS_MEMFD_CREATE未实现
		Pread64Test.Overflow

	if mode == FileMode::O_WRONLY \|\| mode.contains(FileMode::O_PATH) {
	if mode.accmode() == FileMode::O_WRONLY.bits() \|\| mode.contains(FileMode::O_PATH) {

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fix(vfs): 修复 pread64 系统调用的兼容性和错误处理 #1398

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kaleidoscope416 commented Nov 21, 2025 •

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