Refactor git command package to improve security and maintainability (#…

…22678)

This PR follows #21535 (and replace #22592)

## Review without space diff

https://github.com/go-gitea/gitea/pull/22678/files?diff=split&w=1

## Purpose of this PR

1. Make git module command completely safe (risky user inputs won't be
passed as argument option anymore)
2. Avoid low-level mistakes like
#22098 (comment)
3. Remove deprecated and dirty `CmdArgCheck` function, hide the `CmdArg`
type
4. Simplify code when using git command

## The main idea of this PR

* Move the `git.CmdArg` to the `internal` package, then no other package
except `git` could use it. Then developers could never do
`AddArguments(git.CmdArg(userInput))` any more.
* Introduce `git.ToTrustedCmdArgs`, it's for user-provided and already
trusted arguments. It's only used in a few cases, for example: use git
arguments from config file, help unit test with some arguments.
* Introduce `AddOptionValues` and `AddOptionFormat`, they make code more
clear and simple:
    * Before: `AddArguments("-m").AddDynamicArguments(message)`
    * After: `AddOptionValues("-m", message)`
    * -
* Before: `AddArguments(git.CmdArg(fmt.Sprintf("--author='%s <%s>'",
sig.Name, sig.Email)))`
* After: `AddOptionFormat("--author='%s <%s>'", sig.Name, sig.Email)`

## FAQ

### Why these changes were not done in #21535 ?

#21535 is mainly a search&replace, it did its best to not change too
much logic.

Making the framework better needs a lot of changes, so this separate PR
is needed as the second step.


### The naming of `AddOptionXxx`

According to git's manual, the `--xxx` part is called `option`.

### How can it guarantee that `internal.CmdArg` won't be not misused?

Go's specification guarantees that. Trying to access other package's
internal package causes compilation error.

And, `golangci-lint` also denies the git/internal package. Only the
`git/command.go` can use it carefully.

### There is still a `ToTrustedCmdArgs`, will it still allow developers
to make mistakes and pass untrusted arguments?

Generally speaking, no. Because when using `ToTrustedCmdArgs`, the code
will be very complex (see the changes for examples). Then developers and
reviewers can know that something might be unreasonable.

### Why there was a `CmdArgCheck` and why it's removed?

At the moment of #21535, to reduce unnecessary changes, `CmdArgCheck`
was introduced as a hacky patch. Now, almost all code could be written
as `cmd := NewCommand(); cmd.AddXxx(...)`, then there is no need for
`CmdArgCheck` anymore.


### Why many codes for `signArg == ""` is deleted?

Because in the old code, `signArg` could never be empty string, it's
either `-S[key-id]` or `--no-gpg-sign`. So the `signArg == ""` is just
dead code.

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

.golangci.yml

@@ -84,6 +84,7 @@ linters-settings:
       - github.com/unknwon/com: "use gitea's util and replacements"
       - io/ioutil: "use os or io instead"
       - golang.org/x/exp: "it's experimental and unreliable."
+      - code.gitea.io/gitea/modules/git/internal: "do not use the internal package, use AddXxx function instead"
 
 issues:
   max-issues-per-linter: 0

modules/git/command.go

@@ -16,14 +16,20 @@ import (
 	"time"
 	"unsafe"
 
+	"code.gitea.io/gitea/modules/git/internal" //nolint:depguard // only this file can use the internal type CmdArg, other files and packages should use AddXxx functions
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/process"
 	"code.gitea.io/gitea/modules/util"
 )
 
+// TrustedCmdArgs returns the trusted arguments for git command.
+// It's mainly for passing user-provided and trusted arguments to git command
+// In most cases, it shouldn't be used. Use AddXxx function instead
+type TrustedCmdArgs []internal.CmdArg
+
 var (
 	// globalCommandArgs global command args for external package setting
-	globalCommandArgs []CmdArg
+	globalCommandArgs TrustedCmdArgs
 
 	// defaultCommandExecutionTimeout default command execution timeout duration
 	defaultCommandExecutionTimeout = 360 * time.Second
@@ -42,8 +48,6 @@ type Command struct {
 	brokenArgs       []string
 }
 
-type CmdArg string
-
 func (c *Command) String() string {
 	if len(c.args) == 0 {
 		return c.name
@@ -53,7 +57,7 @@ func (c *Command) String() string {
 
 // NewCommand creates and returns a new Git Command based on given command and arguments.
 // Each argument should be safe to be trusted. User-provided arguments should be passed to AddDynamicArguments instead.
-func NewCommand(ctx context.Context, args ...CmdArg) *Command {
+func NewCommand(ctx context.Context, args ...internal.CmdArg) *Command {
 	// Make an explicit copy of globalCommandArgs, otherwise append might overwrite it
 	cargs := make([]string, 0, len(globalCommandArgs)+len(args))
 	for _, arg := range globalCommandArgs {
@@ -70,15 +74,9 @@ func NewCommand(ctx context.Context, args ...CmdArg) *Command {
 	}
 }
 
-// NewCommandNoGlobals creates and returns a new Git Command based on given command and arguments only with the specify args and don't care global command args
-// Each argument should be safe to be trusted. User-provided arguments should be passed to AddDynamicArguments instead.
-func NewCommandNoGlobals(args ...CmdArg) *Command {
-	return NewCommandContextNoGlobals(DefaultContext, args...)
-}
-
 // NewCommandContextNoGlobals creates and returns a new Git Command based on given command and arguments only with the specify args and don't care global command args
 // Each argument should be safe to be trusted. User-provided arguments should be passed to AddDynamicArguments instead.
-func NewCommandContextNoGlobals(ctx context.Context, args ...CmdArg) *Command {
+func NewCommandContextNoGlobals(ctx context.Context, args ...internal.CmdArg) *Command {
 	cargs := make([]string, 0, len(args))
 	for _, arg := range args {
 		cargs = append(cargs, string(arg))
@@ -96,27 +94,70 @@ func (c *Command) SetParentContext(ctx context.Context) *Command {
 	return c
 }
 
-// SetDescription sets the description for this command which be returned on
-// c.String()
+// SetDescription sets the description for this command which be returned on c.String()
 func (c *Command) SetDescription(desc string) *Command {
 	c.desc = desc
 	return c
 }
 
-// AddArguments adds new git argument(s) to the command. Each argument must be safe to be trusted.
-// User-provided arguments should be passed to AddDynamicArguments instead.
-func (c *Command) AddArguments(args ...CmdArg) *Command {
+// isSafeArgumentValue checks if the argument is safe to be used as a value (not an option)
+func isSafeArgumentValue(s string) bool {
+	return s == "" || s[0] != '-'
+}
+
+// isValidArgumentOption checks if the argument is a valid option (starting with '-').
+// It doesn't check whether the option is supported or not
+func isValidArgumentOption(s string) bool {
+	return s != "" && s[0] == '-'
+}
+
+// AddArguments adds new git arguments (option/value) to the command. It only accepts string literals, or trusted CmdArg.
+// Type CmdArg is in the internal package, so it can not be used outside of this package directly,
+// it makes sure that user-provided arguments won't cause RCE risks.
+// User-provided arguments should be passed by other AddXxx functions
+func (c *Command) AddArguments(args ...internal.CmdArg) *Command {
 	for _, arg := range args {
 		c.args = append(c.args, string(arg))
 	}
 	return c
 }
 
-// AddDynamicArguments adds new dynamic argument(s) to the command.
-// The arguments may come from user input and can not be trusted, so no leading '-' is allowed to avoid passing options
+// AddOptionValues adds a new option with a list of non-option values
+// For example: AddOptionValues("--opt", val) means 2 arguments: {"--opt", val}.
+// The values are treated as dynamic argument values. It equals to: AddArguments("--opt") then AddDynamicArguments(val).
+func (c *Command) AddOptionValues(opt internal.CmdArg, args ...string) *Command {
+	if !isValidArgumentOption(string(opt)) {
+		c.brokenArgs = append(c.brokenArgs, string(opt))
+		return c
+	}
+	c.args = append(c.args, string(opt))
+	c.AddDynamicArguments(args...)
+	return c
+}
+
+// AddOptionFormat adds a new option with a format string and arguments
+// For example: AddOptionFormat("--opt=%s %s", val1, val2) means 1 argument: {"--opt=val1 val2"}.
+func (c *Command) AddOptionFormat(opt string, args ...any) *Command {
+	if !isValidArgumentOption(opt) {
+		c.brokenArgs = append(c.brokenArgs, opt)
+		return c
+	}
+	// a quick check to make sure the format string matches the number of arguments, to find low-level mistakes ASAP
+	if strings.Count(strings.ReplaceAll(opt, "%%", ""), "%") != len(args) {
+		c.brokenArgs = append(c.brokenArgs, opt)
+		return c
+	}
+	s := fmt.Sprintf(opt, args...)
+	c.args = append(c.args, s)
+	return c
+}
+
+// AddDynamicArguments adds new dynamic argument values to the command.
+// The arguments may come from user input and can not be trusted, so no leading '-' is allowed to avoid passing options.
+// TODO: in the future, this function can be renamed to AddArgumentValues
 func (c *Command) AddDynamicArguments(args ...string) *Command {
 	for _, arg := range args {
-		if arg != "" && arg[0] == '-' {
+		if !isSafeArgumentValue(arg) {
 			c.brokenArgs = append(c.brokenArgs, arg)
 		}
 	}
@@ -137,14 +178,14 @@ func (c *Command) AddDashesAndList(list ...string) *Command {
 	return c
 }
 
-// CmdArgCheck checks whether the string is safe to be used as a dynamic argument.
-// It panics if the check fails. Usually it should not be used, it's just for refactoring purpose
-// deprecated
-func CmdArgCheck(s string) CmdArg {
-	if s != "" && s[0] == '-' {
-		panic("invalid git cmd argument: " + s)
+// ToTrustedCmdArgs converts a list of strings (trusted as argument) to TrustedCmdArgs
+// In most cases, it shouldn't be used. Use AddXxx function instead
+func ToTrustedCmdArgs(args []string) TrustedCmdArgs {
+	ret := make(TrustedCmdArgs, len(args))
+	for i, arg := range args {
+		ret[i] = internal.CmdArg(arg)
 	}
-	return CmdArg(s)
+	return ret
 }
 
 // RunOpts represents parameters to run the command. If UseContextTimeout is specified, then Timeout is ignored.
@@ -364,9 +405,9 @@ func (c *Command) RunStdBytes(opts *RunOpts) (stdout, stderr []byte, runErr RunS
 }
 
 // AllowLFSFiltersArgs return globalCommandArgs with lfs filter, it should only be used for tests
-func AllowLFSFiltersArgs() []CmdArg {
+func AllowLFSFiltersArgs() TrustedCmdArgs {
 	// Now here we should explicitly allow lfs filters to run
-	filteredLFSGlobalArgs := make([]CmdArg, len(globalCommandArgs))
+	filteredLFSGlobalArgs := make(TrustedCmdArgs, len(globalCommandArgs))
 	j := 0
 	for _, arg := range globalCommandArgs {
 		if strings.Contains(string(arg), "lfs") {

modules/git/command_test.go

@@ -41,3 +41,14 @@ func TestRunWithContextStd(t *testing.T) {
 	assert.Empty(t, stderr)
 	assert.Contains(t, stdout, "git version")
 }
+
+func TestGitArgument(t *testing.T) {
+	assert.True(t, isValidArgumentOption("-x"))
+	assert.True(t, isValidArgumentOption("--xx"))
+	assert.False(t, isValidArgumentOption(""))
+	assert.False(t, isValidArgumentOption("x"))
+
+	assert.True(t, isSafeArgumentValue(""))
+	assert.True(t, isSafeArgumentValue("x"))
+	assert.False(t, isSafeArgumentValue("-x"))
+}

modules/git/commit.go

@@ -9,7 +9,6 @@ import (
 	"bytes"
 	"context"
 	"errors"
-	"fmt"
 	"io"
 	"os/exec"
 	"strconv"
@@ -91,8 +90,8 @@ func AddChanges(repoPath string, all bool, files ...string) error {
 }
 
 // AddChangesWithArgs marks local changes to be ready for commit.
-func AddChangesWithArgs(repoPath string, globalArgs []CmdArg, all bool, files ...string) error {
-	cmd := NewCommandNoGlobals(append(globalArgs, "add")...)
+func AddChangesWithArgs(repoPath string, globalArgs TrustedCmdArgs, all bool, files ...string) error {
+	cmd := NewCommandContextNoGlobals(DefaultContext, globalArgs...).AddArguments("add")
 	if all {
 		cmd.AddArguments("--all")
 	}
@@ -111,27 +110,28 @@ type CommitChangesOptions struct {
 // CommitChanges commits local changes with given committer, author and message.
 // If author is nil, it will be the same as committer.
 func CommitChanges(repoPath string, opts CommitChangesOptions) error {
-	cargs := make([]CmdArg, len(globalCommandArgs))
+	cargs := make(TrustedCmdArgs, len(globalCommandArgs))
 	copy(cargs, globalCommandArgs)
 	return CommitChangesWithArgs(repoPath, cargs, opts)
 }
 
 // CommitChangesWithArgs commits local changes with given committer, author and message.
 // If author is nil, it will be the same as committer.
-func CommitChangesWithArgs(repoPath string, args []CmdArg, opts CommitChangesOptions) error {
-	cmd := NewCommandNoGlobals(args...)
+func CommitChangesWithArgs(repoPath string, args TrustedCmdArgs, opts CommitChangesOptions) error {
+	cmd := NewCommandContextNoGlobals(DefaultContext, args...)
 	if opts.Committer != nil {
-		cmd.AddArguments("-c", CmdArg("user.name="+opts.Committer.Name), "-c", CmdArg("user.email="+opts.Committer.Email))
+		cmd.AddOptionValues("-c", "user.name="+opts.Committer.Name)
+		cmd.AddOptionValues("-c", "user.email="+opts.Committer.Email)
 	}
 	cmd.AddArguments("commit")
 
 	if opts.Author == nil {
 		opts.Author = opts.Committer
 	}
 	if opts.Author != nil {
-		cmd.AddArguments(CmdArg(fmt.Sprintf("--author='%s <%s>'", opts.Author.Name, opts.Author.Email)))
+		cmd.AddOptionFormat("--author='%s <%s>'", opts.Author.Name, opts.Author.Email)
 	}
-	cmd.AddArguments("-m").AddDynamicArguments(opts.Message)
+	cmd.AddOptionValues("-m", opts.Message)
 
 	_, _, err := cmd.RunStdString(&RunOpts{Dir: repoPath})
 	// No stderr but exit status 1 means nothing to commit.

modules/git/git.go

@@ -383,6 +383,6 @@ func configUnsetAll(key, value string) error {
 }
 
 // Fsck verifies the connectivity and validity of the objects in the database
-func Fsck(ctx context.Context, repoPath string, timeout time.Duration, args ...CmdArg) error {
+func Fsck(ctx context.Context, repoPath string, timeout time.Duration, args TrustedCmdArgs) error {
 	return NewCommand(ctx, "fsck").AddArguments(args...).Run(&RunOpts{Timeout: timeout, Dir: repoPath})
 }

modules/git/internal/cmdarg.go

@@ -0,0 +1,9 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package internal
+
+// CmdArg represents a command argument for git command, and it will be used for the git command directly without any further processing.
+// In most cases, you should use the "AddXxx" functions to add arguments, but not use this type directly.
+// Casting a risky (user-provided) string to CmdArg would cause security issues if it's injected with a "--xxx" argument.
+type CmdArg string

modules/git/repo.go

@@ -115,7 +115,7 @@ func Clone(ctx context.Context, from, to string, opts CloneRepoOptions) error {
 }
 
 // CloneWithArgs original repository to target path.
-func CloneWithArgs(ctx context.Context, args []CmdArg, from, to string, opts CloneRepoOptions) (err error) {
+func CloneWithArgs(ctx context.Context, args TrustedCmdArgs, from, to string, opts CloneRepoOptions) (err error) {
 	toDir := path.Dir(to)
 	if err = os.MkdirAll(toDir, os.ModePerm); err != nil {
 		return err

modules/git/repo_archive.go

@@ -57,9 +57,9 @@ func (repo *Repository) CreateArchive(ctx context.Context, format ArchiveType, t
 
 	cmd := NewCommand(ctx, "archive")
 	if usePrefix {
-		cmd.AddArguments(CmdArg("--prefix=" + filepath.Base(strings.TrimSuffix(repo.Path, ".git")) + "/"))
+		cmd.AddOptionFormat("--prefix=%s", filepath.Base(strings.TrimSuffix(repo.Path, ".git"))+"/")
 	}
-	cmd.AddArguments(CmdArg("--format=" + format.String()))
+	cmd.AddOptionFormat("--format=%s", format.String())
 	cmd.AddDynamicArguments(commitID)
 
 	var stderr strings.Builder

modules/git/repo_attribute.go

@@ -17,7 +17,7 @@ import (
 type CheckAttributeOpts struct {
 	CachedOnly    bool
 	AllAttributes bool
-	Attributes    []CmdArg
+	Attributes    []string
 	Filenames     []string
 	IndexFile     string
 	WorkTree      string
@@ -48,7 +48,7 @@ func (repo *Repository) CheckAttribute(opts CheckAttributeOpts) (map[string]map[
 	} else {
 		for _, attribute := range opts.Attributes {
 			if attribute != "" {
-				cmd.AddArguments(attribute)
+				cmd.AddDynamicArguments(attribute)
 			}
 		}
 	}
@@ -95,7 +95,7 @@ func (repo *Repository) CheckAttribute(opts CheckAttributeOpts) (map[string]map[
 // CheckAttributeReader provides a reader for check-attribute content that can be long running
 type CheckAttributeReader struct {
 	// params
-	Attributes []CmdArg
+	Attributes []string
 	Repo       *Repository
 	IndexFile  string
 	WorkTree   string
@@ -111,19 +111,6 @@ type CheckAttributeReader struct {
 
 // Init initializes the CheckAttributeReader
 func (c *CheckAttributeReader) Init(ctx context.Context) error {
-	cmdArgs := []CmdArg{"check-attr", "--stdin", "-z"}
-
-	if len(c.IndexFile) > 0 {
-		cmdArgs = append(cmdArgs, "--cached")
-		c.env = append(c.env, "GIT_INDEX_FILE="+c.IndexFile)
-	}
-
-	if len(c.WorkTree) > 0 {
-		c.env = append(c.env, "GIT_WORK_TREE="+c.WorkTree)
-	}
-
-	c.env = append(c.env, "GIT_FLUSH=1")
-
 	if len(c.Attributes) == 0 {
 		lw := new(nulSeparatedAttributeWriter)
 		lw.attributes = make(chan attributeTriple)
@@ -134,11 +121,22 @@ func (c *CheckAttributeReader) Init(ctx context.Context) error {
 		return fmt.Errorf("no provided Attributes to check")
 	}
 
-	cmdArgs = append(cmdArgs, c.Attributes...)
-	cmdArgs = append(cmdArgs, "--")
-
 	c.ctx, c.cancel = context.WithCancel(ctx)
-	c.cmd = NewCommand(c.ctx, cmdArgs...)
+	c.cmd = NewCommand(c.ctx, "check-attr", "--stdin", "-z")
+
+	if len(c.IndexFile) > 0 {
+		c.cmd.AddArguments("--cached")
+		c.env = append(c.env, "GIT_INDEX_FILE="+c.IndexFile)
+	}
+
+	if len(c.WorkTree) > 0 {
+		c.env = append(c.env, "GIT_WORK_TREE="+c.WorkTree)
+	}
+
+	c.env = append(c.env, "GIT_FLUSH=1")
+
+	// The empty "--" comes from #16773 , and it seems unnecessary because nothing else would be added later.
+	c.cmd.AddDynamicArguments(c.Attributes...).AddArguments("--")
 
 	var err error
 
@@ -294,7 +292,7 @@ func (repo *Repository) CheckAttributeReader(commitID string) (*CheckAttributeRe
 	}
 
 	checker := &CheckAttributeReader{
-		Attributes: []CmdArg{"linguist-vendored", "linguist-generated", "linguist-language", "gitlab-language"},
+		Attributes: []string{"linguist-vendored", "linguist-generated", "linguist-language", "gitlab-language"},
 		Repo:       repo,
 		IndexFile:  indexFilename,
 		WorkTree:   worktree,

modules/git/repo_blame.go

@@ -3,7 +3,9 @@
 
 package git
 
-import "fmt"
+import (
+	"fmt"
+)
 
 // FileBlame return the Blame object of file
 func (repo *Repository) FileBlame(revision, path, file string) ([]byte, error) {
@@ -14,8 +16,8 @@ func (repo *Repository) FileBlame(revision, path, file string) ([]byte, error) {
 // LineBlame returns the latest commit at the given line
 func (repo *Repository) LineBlame(revision, path, file string, line uint) (*Commit, error) {
 	res, _, err := NewCommand(repo.Ctx, "blame").
-		AddArguments(CmdArg(fmt.Sprintf("-L %d,%d", line, line))).
-		AddArguments("-p").AddDynamicArguments(revision).
+		AddOptionFormat("-L %d,%d", line, line).
+		AddOptionValues("-p", revision).
 		AddDashesAndList(file).RunStdString(&RunOpts{Dir: path})
 	if err != nil {
 		return nil, err