Add support for ssh commit signing (#17743)

* Add support for ssh commit signing

* Split out ssh verification to separate file

* Show ssh key fingerprint on commit page

* Update sshsig lib

* Make sure we verify against correct namespace

* Add ssh public key verification via ssh signatures

When adding a public ssh key also validate that this user actually
owns the key by signing a token with the private key.

* Remove some gpg references and make verify key optional

* Fix spaces indentation

* Update options/locale/locale_en-US.ini

Co-authored-by: Gusted <williamzijl7@hotmail.com>

* Update templates/user/settings/keys_ssh.tmpl

Co-authored-by: Gusted <williamzijl7@hotmail.com>

* Update options/locale/locale_en-US.ini

Co-authored-by: Gusted <williamzijl7@hotmail.com>

* Update options/locale/locale_en-US.ini

Co-authored-by: Gusted <williamzijl7@hotmail.com>

* Update models/ssh_key_commit_verification.go

Co-authored-by: Gusted <williamzijl7@hotmail.com>

* Reword ssh/gpg_key_success message

* Change Badsignature to NoKeyFound

* Add sign/verify tests

* Fix upstream api changes to user_model User

* Match exact on SSH signature

* Fix code review remarks

Co-authored-by: Gusted <williamzijl7@hotmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

vendor/golang.org/x/sys/unix/sysvshm_unix.go

@@ -0,0 +1,61 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build (darwin && !ios) || linux
+// +build darwin,!ios linux
+
+package unix
+
+import (
+	"unsafe"
+
+	"golang.org/x/sys/internal/unsafeheader"
+)
+
+// SysvShmAttach attaches the Sysv shared memory segment associated with the
+// shared memory identifier id.
+func SysvShmAttach(id int, addr uintptr, flag int) ([]byte, error) {
+	addr, errno := shmat(id, addr, flag)
+	if errno != nil {
+		return nil, errno
+	}
+
+	// Retrieve the size of the shared memory to enable slice creation
+	var info SysvShmDesc
+
+	_, err := SysvShmCtl(id, IPC_STAT, &info)
+	if err != nil {
+		// release the shared memory if we can't find the size
+
+		// ignoring error from shmdt as there's nothing sensible to return here
+		shmdt(addr)
+		return nil, err
+	}
+
+	// Use unsafe to convert addr into a []byte.
+	// TODO: convert to unsafe.Slice once we can assume Go 1.17
+	var b []byte
+	hdr := (*unsafeheader.Slice)(unsafe.Pointer(&b))
+	hdr.Data = unsafe.Pointer(addr)
+	hdr.Cap = int(info.Segsz)
+	hdr.Len = int(info.Segsz)
+	return b, nil
+}
+
+// SysvShmDetach unmaps the shared memory slice returned from SysvShmAttach.
+//
+// It is not safe to use the slice after calling this function.
+func SysvShmDetach(data []byte) error {
+	if len(data) == 0 {
+		return EINVAL
+	}
+
+	return shmdt(uintptr(unsafe.Pointer(&data[0])))
+}
+
+// SysvShmGet returns the Sysv shared memory identifier associated with key.
+// If the IPC_CREAT flag is specified a new segment is created.
+func SysvShmGet(key, size, flag int) (id int, err error) {
+	return shmget(key, size, flag)
+}