smb3: allow decryption keys to be dumped by admin for debugging

In order to debug certain problems it is important to be able
to decrypt network traces (e.g. wireshark) but to do this we
need to be able to dump out the encryption/decryption keys.
Dumping them to an ioctl is safer than dumping then to dmesg,
(and better than showing all keys in a pseudofile).

Restrict this to root (CAP_SYS_ADMIN), and only for a mount
that this admin has access to.

Sample smbinfo output:
SMB3.0 encryption
Session Id:   0x82d2ec52
Session Key:  a5 6d 81 d0 e c1 ca e1 d8 13 aa 20 e8 f2 cc 71
Server Encryption Key:  1a c3 be ba 3d fc dc 3c e bc 93 9e 50 9e 19 c1
Server Decryption Key:  e0 d4 d9 43 1b a2 1b e3 d8 76 77 49 56 f7 20 88
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifs_ioctl.h

@@ -57,9 +57,18 @@ struct smb_query_info {
 	/* char buffer[]; */
 } __packed;
 
+struct smb3_key_debug_info {
+	__u64	Suid;
+	__u16	cipher_type;
+	__u8	auth_key[16]; /* SMB2_NTLMV2_SESSKEY_SIZE */
+	__u8	smb3encryptionkey[SMB3_SIGN_KEY_SIZE];
+	__u8	smb3decryptionkey[SMB3_SIGN_KEY_SIZE];
+} __packed;
+
 #define CIFS_IOCTL_MAGIC	0xCF
 #define CIFS_IOC_COPYCHUNK_FILE	_IOW(CIFS_IOCTL_MAGIC, 3, int)
 #define CIFS_IOC_SET_INTEGRITY  _IO(CIFS_IOCTL_MAGIC, 4)
 #define CIFS_IOC_GET_MNT_INFO _IOR(CIFS_IOCTL_MAGIC, 5, struct smb_mnt_fs_info)
 #define CIFS_ENUMERATE_SNAPSHOTS _IOR(CIFS_IOCTL_MAGIC, 6, struct smb_snapshot_array)
 #define CIFS_QUERY_INFO _IOWR(CIFS_IOCTL_MAGIC, 7, struct smb_query_info)
+#define CIFS_DUMP_KEY _IOWR(CIFS_IOCTL_MAGIC, 8, struct smb3_key_debug_info)

fs/cifs/ioctl.c

@@ -164,6 +164,7 @@ static long smb_mnt_get_fsinfo(unsigned int xid, struct cifs_tcon *tcon,
 long cifs_ioctl(struct file *filep, unsigned int command, unsigned long arg)
 {
 	struct inode *inode = file_inode(filep);
+	struct smb3_key_debug_info pkey_inf;
 	int rc = -ENOTTY; /* strange error - but the precedent */
 	unsigned int xid;
 	struct cifsFileInfo *pSMBFile = filep->private_data;
@@ -270,6 +271,34 @@ long cifs_ioctl(struct file *filep, unsigned int command, unsigned long arg)
 			else
 				rc = -EOPNOTSUPP;
 			break;
+		case CIFS_DUMP_KEY:
+			if (pSMBFile == NULL)
+				break;
+			if (!capable(CAP_SYS_ADMIN)) {
+				rc = -EACCES;
+				break;
+			}
+
+			tcon = tlink_tcon(pSMBFile->tlink);
+			if (!smb3_encryption_required(tcon)) {
+				rc = -EOPNOTSUPP;
+				break;
+			}
+			pkey_inf.cipher_type =
+				le16_to_cpu(tcon->ses->server->cipher_type);
+			pkey_inf.Suid = tcon->ses->Suid;
+			memcpy(pkey_inf.auth_key, tcon->ses->auth_key.response,
+					16 /* SMB2_NTLMV2_SESSKEY_SIZE */);
+			memcpy(pkey_inf.smb3decryptionkey,
+			      tcon->ses->smb3decryptionkey, SMB3_SIGN_KEY_SIZE);
+			memcpy(pkey_inf.smb3encryptionkey,
+			      tcon->ses->smb3encryptionkey, SMB3_SIGN_KEY_SIZE);
+			if (copy_to_user((void __user *)arg, &pkey_inf,
+					sizeof(struct smb3_key_debug_info)))
+				rc = -EFAULT;
+			else
+				rc = 0;
+			break;
 		default:
 			cifs_dbg(FYI, "unsupported ioctl\n");
 			break;