[PATCH] smb3.1.1: allow dumping GCM256 keys to improve debugging of encrypted shares

[ronnie sahlberg]

These elements should probably be [32] and not
+ __u8 smb3encryptionkey[SMB3_ENC_DEC_KEY_SIZE];

Because this is now visible to userspace and we can not allow this to
ever change.
Because when GCM512 is eventually released, if we bump
SMB3_ENC_DEC_KEY_SIZE to a larger value we suddenly break userspace.


On Sat, May 1, 2021 at 8:20 AM Steve French <smfrench at gmail.com> wrote:
>
> Previously we were only able to dump CCM or GCM-128 keys (see "smbinfo
> keys" e.g.)
> to allow network debugging (e.g. wireshark) of mounts to SMB3.1.1 encrypted
> shares.  But with the addition of GCM-256 support, we have to be able to dump
> 32 byte instead of 16 byte keys which requires adding an additional ioctl
> for that.
>
> Signed-off-by: Steve French <stfrench at microsoft.com>
> ---
>  fs/cifs/cifs_ioctl.h | 19 +++++++++++++++++++
>  fs/cifs/ioctl.c      | 33 +++++++++++++++++++++++++++++++++
>  2 files changed, 52 insertions(+)
>
> diff --git a/fs/cifs/cifs_ioctl.h b/fs/cifs/cifs_ioctl.h
> index f262c64516bc..9f2ed9cccb08 100644
> --- a/fs/cifs/cifs_ioctl.h
> +++ b/fs/cifs/cifs_ioctl.h
> @@ -57,6 +57,12 @@ struct smb_query_info {
>   /* char buffer[]; */
>  } __packed;
>
> +/*
> + * Dumping the commonly used 16 byte (e.g. CCM and GCM128) keys still supported
> + * for backlevel compatibility, but is not sufficient for dumping the less
> + * frequently used GCM256 (32 byte) keys (see the newer "CIFS_DUMP_FULL_KEY"
> + * ioctl for dumping decryption info for GCM256 mounts)
> + */
>  struct smb3_key_debug_info {
>   __u64 Suid;
>   __u16 cipher_type;
> @@ -65,6 +71,18 @@ struct smb3_key_debug_info {
>   __u8 smb3decryptionkey[SMB3_SIGN_KEY_SIZE];
>  } __packed;
>
> +/*
> + * Dump full key (32 byte encrypt/decrypt keys instead of 16 bytes)
> + * is needed if GCM256 (stronger encryption) negotiated
> + */
> +struct smb3_full_key_debug_info {
> + __u64 Suid;
> + __u16 cipher_type;
> + __u8 auth_key[16]; /* SMB2_NTLMV2_SESSKEY_SIZE */
> + __u8 smb3encryptionkey[SMB3_ENC_DEC_KEY_SIZE];
> + __u8 smb3decryptionkey[SMB3_ENC_DEC_KEY_SIZE];
> +} __packed;
> +
>  struct smb3_notify {
>   __u32 completion_filter;
>   bool watch_tree;
> @@ -78,6 +96,7 @@ struct smb3_notify {
>  #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)
>  #define CIFS_IOC_NOTIFY _IOW(CIFS_IOCTL_MAGIC, 9, struct smb3_notify)
> +#define CIFS_DUMP_FULL_KEY _IOWR(CIFS_IOCTL_MAGIC, 10, struct
> smb3_full_key_debug_info)
>  #define CIFS_IOC_SHUTDOWN _IOR ('X', 125, __u32)
>
>  /*
> diff --git a/fs/cifs/ioctl.c b/fs/cifs/ioctl.c
> index ef41fa878793..e4321e2a27d2 100644
> --- a/fs/cifs/ioctl.c
> +++ b/fs/cifs/ioctl.c
> @@ -218,6 +218,7 @@ 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;
> + struct smb3_full_key_debug_info pfull_key_inf;
>   int rc = -ENOTTY; /* strange error - but the precedent */
>   unsigned int xid;
>   struct cifsFileInfo *pSMBFile = filep->private_data;
> @@ -354,6 +355,38 @@ long cifs_ioctl(struct file *filep, unsigned int
> command, unsigned long arg)
>   else
>   rc = 0;
>   break;
> + /*
> + * Dump full key (32 bytes instead of 16 bytes) is
> + * needed if GCM256 (stronger encryption) negotiated
> + */
> + case CIFS_DUMP_FULL_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;
> + }
> + pfull_key_inf.cipher_type =
> + le16_to_cpu(tcon->ses->server->cipher_type);
> + pfull_key_inf.Suid = tcon->ses->Suid;
> + memcpy(pfull_key_inf.auth_key, tcon->ses->auth_key.response,
> + 16 /* SMB2_NTLMV2_SESSKEY_SIZE */);
> + memcpy(pfull_key_inf.smb3decryptionkey,
> +       tcon->ses->smb3decryptionkey, SMB3_ENC_DEC_KEY_SIZE);
> + memcpy(pfull_key_inf.smb3encryptionkey,
> +       tcon->ses->smb3encryptionkey, SMB3_ENC_DEC_KEY_SIZE);
> + if (copy_to_user((void __user *)arg, &pfull_key_inf,
> + sizeof(struct smb3_full_key_debug_info)))
> + rc = -EFAULT;
> + else
> + rc = 0;
> + break;
>   case CIFS_IOC_NOTIFY:
>   if (!S_ISDIR(inode->i_mode)) {
>   /* Notify can only be done on directories */
>
> --
> Thanks,
>
> Steve