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fix: return 400 instead of 500 for user-caused process start failures #197

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Merged
hiroTamada merged 2 commits into from
Apr 1, 2026
+43 −0
Merged

fix: return 400 instead of 500 for user-caused process start failures #197

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55efa13
fix: return 400 instead of 500 for user-caused process start failures
hiroTamada Apr 1, 2026
30d1881
broaden isUserCmdError per review feedback
hiroTamada Apr 1, 2026
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19 changes: 19 additions & 0 deletions server/cmd/api/api/process.go
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Original file line number Diff line number Diff line change
Expand Up @@ -64,6 +64,16 @@ func (h *processHandle) setExited(code int) {
h.mu.Unlock()
}

func isUserCmdError(err error) bool {
return errors.Is(err, exec.ErrNotFound) ||
errors.Is(err, exec.ErrDot) ||
errors.Is(err, os.ErrNotExist) ||
errors.Is(err, os.ErrPermission) ||
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@cursor cursor bot Apr 1, 2026

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os.ErrPermission catches server-side EPERM as user error

Medium Severity

errors.Is(err, os.ErrPermission) matches both syscall.EACCES and syscall.EPERM due to Go's Errno.Is mapping. Only EACCES (file permission denied) is a user-input error. EPERM (operation not permitted) can arise from server-side issues — most notably when AsRoot or AsUser sets SysProcAttr.Credential but the server lacks CAP_SETUID/CAP_SETGID. In that case cmd.Start() fails with EPERM, which gets misclassified as a 400 instead of 500, masking a server configuration problem. Using syscall.EACCES directly instead of os.ErrPermission would avoid catching EPERM.

Additional Locations (1)
Fix in Cursor Fix in Web

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@hiroTamada hiroTamada Apr 1, 2026

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I think 400 is fine for now in this case

errors.Is(err, syscall.EISDIR) ||
errors.Is(err, syscall.ENOEXEC) ||
errors.Is(err, syscall.ENOTDIR)
}

func buildCmd(body *oapi.ProcessExecRequest) (*exec.Cmd, error) {
if body == nil || body.Command == "" {
return nil, errors.New("command required")
Expand Down Expand Up @@ -177,6 +187,9 @@ func (s *ApiService) ProcessExec(ctx context.Context, request oapi.ProcessExecRe
defer cancel()
}
if err := cmd.Start(); err != nil {
if isUserCmdError(err) {
return oapi.ProcessExec400JSONResponse{BadRequestErrorJSONResponse: oapi.BadRequestErrorJSONResponse{Message: err.Error()}}, nil
}
log.Error("failed to start process", "err", err)
return oapi.ProcessExec500JSONResponse{InternalErrorJSONResponse: oapi.InternalErrorJSONResponse{Message: "failed to start process"}}, nil
}
Expand Down Expand Up @@ -263,6 +276,9 @@ func (s *ApiService) ProcessSpawn(ctx context.Context, request oapi.ProcessSpawn
var errStart error
ptyFile, errStart = pty.Start(cmd)
if errStart != nil {
if isUserCmdError(errStart) {
return oapi.ProcessSpawn400JSONResponse{BadRequestErrorJSONResponse: oapi.BadRequestErrorJSONResponse{Message: errStart.Error()}}, nil
}
log.Error("failed to start PTY process", "err", errStart)
return oapi.ProcessSpawn500JSONResponse{InternalErrorJSONResponse: oapi.InternalErrorJSONResponse{Message: "failed to start process"}}, nil
}
Expand Down Expand Up @@ -294,6 +310,9 @@ func (s *ApiService) ProcessSpawn(ctx context.Context, request oapi.ProcessSpawn
return oapi.ProcessSpawn500JSONResponse{InternalErrorJSONResponse: oapi.InternalErrorJSONResponse{Message: "failed to open stdin"}}, nil
}
if err := cmd.Start(); err != nil {
if isUserCmdError(err) {
return oapi.ProcessSpawn400JSONResponse{BadRequestErrorJSONResponse: oapi.BadRequestErrorJSONResponse{Message: err.Error()}}, nil
}
log.Error("failed to start process", "err", err)
return oapi.ProcessSpawn500JSONResponse{InternalErrorJSONResponse: oapi.InternalErrorJSONResponse{Message: "failed to start process"}}, nil
}
Expand Down
24 changes: 24 additions & 0 deletions server/cmd/api/api/process_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -203,6 +203,30 @@ func TestProcessNotFoundRoutes(t *testing.T) {
}
}

func TestProcessExec_CommandNotFound(t *testing.T) {
t.Parallel()
ctx := context.Background()
svc := &ApiService{procs: make(map[string]*processHandle)}

body := &oapi.ProcessExecRequest{Command: "nonexistent_binary_that_does_not_exist"}
resp, err := svc.ProcessExec(ctx, oapi.ProcessExecRequestObject{Body: body})
require.NoError(t, err)
_, ok := resp.(oapi.ProcessExec400JSONResponse)
require.True(t, ok, "expected 400 for nonexistent command, got %T", resp)
}

func TestProcessSpawn_CommandNotFound(t *testing.T) {
t.Parallel()
ctx := context.Background()
svc := &ApiService{procs: make(map[string]*processHandle), stz: scaletozero.NewNoopController()}

body := &oapi.ProcessSpawnRequest{Command: "nonexistent_binary_that_does_not_exist"}
resp, err := svc.ProcessSpawn(ctx, oapi.ProcessSpawnRequestObject{Body: body})
require.NoError(t, err)
_, ok := resp.(oapi.ProcessSpawn400JSONResponse)
require.True(t, ok, "expected 400 for nonexistent command, got %T", resp)
}

func TestBuildCmd_AsRootSetsCredential(t *testing.T) {
t.Parallel()
asRoot := true
Expand Down
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