[PATCH v2 2/6] smb: clear the aes_cmac_key and aes_cmac_ctx when done

[PATCH v2 2/6] smb: clear the aes_cmac_key and aes_cmac_ctx when done

[Thomas Huth]

From: Thomas Huth <thuth@redhat.com>

Clear the local crypto-related structures via __cleanup() functions
when we're done with them to avoid that sensitive data could leak on
the stack.

Note: cmac_ctx in ksmbd_sign_smb3_pdu() gets cleared in aes_cmac_final()
already, so this does not need a __cleanup() marker.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 fs/smb/client/smb2transport.c | 4 ++--
 fs/smb/server/auth.c          | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/smb/client/smb2transport.c b/fs/smb/client/smb2transport.c
index 1143ee52470a7..d23566da2ac81 100644
--- a/fs/smb/client/smb2transport.c
+++ b/fs/smb/client/smb2transport.c
@@ -464,8 +464,8 @@ smb3_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
 	unsigned char smb3_signature[SMB2_CMACAES_SIZE];
 	struct kvec *iov = rqst->rq_iov;
 	struct smb2_hdr *shdr = (struct smb2_hdr *)iov[0].iov_base;
-	struct aes_cmac_key cmac_key;
-	struct aes_cmac_ctx cmac_ctx;
+	struct aes_cmac_key cmac_key __cleanup(aes_cmac_zeroize_key);
+	struct aes_cmac_ctx cmac_ctx __cleanup(aes_cmac_zeroize_ctx);
 	struct smb_rqst drqst;
 	u8 key[SMB3_SIGN_KEY_SIZE];
 
diff --git a/fs/smb/server/auth.c b/fs/smb/server/auth.c
index 4e7b6f0e6b8cd..e8d1c068a43e8 100644
--- a/fs/smb/server/auth.c
+++ b/fs/smb/server/auth.c
@@ -509,7 +509,7 @@ void ksmbd_sign_smb2_pdu(struct ksmbd_conn *conn, char *key, struct kvec *iov,
 void ksmbd_sign_smb3_pdu(struct ksmbd_conn *conn, char *key, struct kvec *iov,
 			 int n_vec, char *sig)
 {
-	struct aes_cmac_key cmac_key;
+	struct aes_cmac_key cmac_key __cleanup(aes_cmac_zeroize_key);
 	struct aes_cmac_ctx cmac_ctx;
 	int i;
 
-- 
2.55.0

Re: [PATCH v2 2/6] smb: clear the aes_cmac_key and aes_cmac_ctx when done

[Namjae Jeon]

> diff --git a/fs/smb/client/smb2transport.c b/fs/smb/client/smb2transport.c
> index 1143ee52470a7..d23566da2ac81 100644
> --- a/fs/smb/client/smb2transport.c
> +++ b/fs/smb/client/smb2transport.c
> @@ -464,8 +464,8 @@ smb3_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
>         unsigned char smb3_signature[SMB2_CMACAES_SIZE];
>         struct kvec *iov = rqst->rq_iov;
>         struct smb2_hdr *shdr = (struct smb2_hdr *)iov[0].iov_base;
> -       struct aes_cmac_key cmac_key;
> -       struct aes_cmac_ctx cmac_ctx;
> +       struct aes_cmac_key cmac_key __cleanup(aes_cmac_zeroize_key);
> +       struct aes_cmac_ctx cmac_ctx __cleanup(aes_cmac_zeroize_ctx);
>         struct smb_rqst drqst;
>         u8 key[SMB3_SIGN_KEY_SIZE];
Shouldn’t we also clear the raw key with memzero_explicit(key,
sizeof(key)) immediately after aes_cmac_preparekey() ?

        rc = aes_cmac_preparekey(&cmac_key, key, SMB2_CMACAES_SIZE);
+        memzero_explicit(key, sizeof(key));
        if (rc) {
                cifs_server_dbg(VFS, "%s: Could not set key for cmac
aes\n", __func__);
                return rc;
        }

Re: [PATCH v2 2/6] smb: clear the aes_cmac_key and aes_cmac_ctx when done

[Thomas Huth]

On 11/08/2026 12.31, Namjae Jeon wrote:
>> diff --git a/fs/smb/client/smb2transport.c b/fs/smb/client/smb2transport.c
>> index 1143ee52470a7..d23566da2ac81 100644
>> --- a/fs/smb/client/smb2transport.c
>> +++ b/fs/smb/client/smb2transport.c
>> @@ -464,8 +464,8 @@ smb3_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
>>          unsigned char smb3_signature[SMB2_CMACAES_SIZE];
>>          struct kvec *iov = rqst->rq_iov;
>>          struct smb2_hdr *shdr = (struct smb2_hdr *)iov[0].iov_base;
>> -       struct aes_cmac_key cmac_key;
>> -       struct aes_cmac_ctx cmac_ctx;
>> +       struct aes_cmac_key cmac_key __cleanup(aes_cmac_zeroize_key);
>> +       struct aes_cmac_ctx cmac_ctx __cleanup(aes_cmac_zeroize_ctx);
>>          struct smb_rqst drqst;
>>          u8 key[SMB3_SIGN_KEY_SIZE];
> Shouldn’t we also clear the raw key with memzero_explicit(key,
> sizeof(key)) immediately after aes_cmac_preparekey() ?
> 
>          rc = aes_cmac_preparekey(&cmac_key, key, SMB2_CMACAES_SIZE);
> +        memzero_explicit(key, sizeof(key));
>          if (rc) {
>                  cifs_server_dbg(VFS, "%s: Could not set key for cmac
> aes\n", __func__);
>                  return rc;
>          }
Yes, but I was planning to do all the scrubbing for such other spots in a 
separate patch series (similar to what I've posted for the smb/server code 
already) ... this patch series here focuses on aes_cmac_zeroize_key and 
aes_cmac_zeroize_ctx only. I hope that's ok?

  Thomas

Re: [PATCH v2 2/6] smb: clear the aes_cmac_key and aes_cmac_ctx when done

[Namjae Jeon]

On Tue, Aug 11, 2026 at 9:57 PM Thomas Huth <thuth@redhat.com> wrote:
>
> On 11/08/2026 12.31, Namjae Jeon wrote:
> >> diff --git a/fs/smb/client/smb2transport.c b/fs/smb/client/smb2transport.c
> >> index 1143ee52470a7..d23566da2ac81 100644
> >> --- a/fs/smb/client/smb2transport.c
> >> +++ b/fs/smb/client/smb2transport.c
> >> @@ -464,8 +464,8 @@ smb3_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
> >>          unsigned char smb3_signature[SMB2_CMACAES_SIZE];
> >>          struct kvec *iov = rqst->rq_iov;
> >>          struct smb2_hdr *shdr = (struct smb2_hdr *)iov[0].iov_base;
> >> -       struct aes_cmac_key cmac_key;
> >> -       struct aes_cmac_ctx cmac_ctx;
> >> +       struct aes_cmac_key cmac_key __cleanup(aes_cmac_zeroize_key);
> >> +       struct aes_cmac_ctx cmac_ctx __cleanup(aes_cmac_zeroize_ctx);
> >>          struct smb_rqst drqst;
> >>          u8 key[SMB3_SIGN_KEY_SIZE];
> > Shouldn’t we also clear the raw key with memzero_explicit(key,
> > sizeof(key)) immediately after aes_cmac_preparekey() ?
> >
> >          rc = aes_cmac_preparekey(&cmac_key, key, SMB2_CMACAES_SIZE);
> > +        memzero_explicit(key, sizeof(key));
> >          if (rc) {
> >                  cifs_server_dbg(VFS, "%s: Could not set key for cmac
> > aes\n", __func__);
> >                  return rc;
> >          }
> Yes, but I was planning to do all the scrubbing for such other spots in a
> separate patch series (similar to what I've posted for the smb/server code
> already) ... this patch series here focuses on aes_cmac_zeroize_key and
> aes_cmac_zeroize_ctx only. I hope that's ok?
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Thanks.