[PATCH] crypto: mxs-dcp: handle zero-length skcipher requests

[PATCH] crypto: mxs-dcp: handle zero-length skcipher requests

[Linmao Li]

Zero-length skcipher requests are valid no-ops, but MXS-DCP queues them.
When such a request reaches the worker, last_out_len remains zero. The
CBC completion path then subtracts AES_BLOCK_SIZE from this unsigned
value when updating the IV, causing the offset to underflow. On
decryption, the resulting source address precedes aes_in_buf.

Return success before enqueueing zero-length requests. This avoids the
invalid source access and leaves the IV unchanged for a no-op.

Fixes: fadd7a6e616b ("crypto: mxs-dcp - Fix AES issues")
Signed-off-by: Linmao Li <lilinmao@kylinos.cn>
---
 drivers/crypto/mxs-dcp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/crypto/mxs-dcp.c b/drivers/crypto/mxs-dcp.c
index 133ebc998236..60794b4d49fa 100644
--- a/drivers/crypto/mxs-dcp.c
+++ b/drivers/crypto/mxs-dcp.c
@@ -473,6 +473,9 @@ static int mxs_dcp_aes_enqueue(struct skcipher_request *req, int enc, int ecb)
 	struct dcp_aes_req_ctx *rctx = skcipher_request_ctx(req);
 	int ret;
 
+	if (!req->cryptlen)
+		return 0;
+
 	if (unlikely(actx->key_len != AES_KEYSIZE_128 && !actx->key_referenced))
 		return mxs_dcp_block_fallback(req, enc);
 

base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
-- 
2.25.1

Re: [PATCH] crypto: mxs-dcp: handle zero-length skcipher requests

[Frank Li]

On Fri, Aug 28, 2026 at 05:32:09PM +0800, Linmao Li wrote:
> [You don't often get email from lilinmao@kylinos.cn. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>
> Zero-length skcipher requests are valid no-ops, but MXS-DCP queues them.

Any document show it? if return 0 when cryptelen, it is async, no
call crypto_request_complete.

Frank

> When such a request reaches the worker, last_out_len remains zero. The
> CBC completion path then subtracts AES_BLOCK_SIZE from this unsigned
> value when updating the IV, causing the offset to underflow. On
> decryption, the resulting source address precedes aes_in_buf.
>
> Return success before enqueueing zero-length requests. This avoids the
> invalid source access and leaves the IV unchanged for a no-op.
>
> Fixes: fadd7a6e616b ("crypto: mxs-dcp - Fix AES issues")
> Signed-off-by: Linmao Li <lilinmao@kylinos.cn>
> ---
>  drivers/crypto/mxs-dcp.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/crypto/mxs-dcp.c b/drivers/crypto/mxs-dcp.c
> index 133ebc998236..60794b4d49fa 100644
> --- a/drivers/crypto/mxs-dcp.c
> +++ b/drivers/crypto/mxs-dcp.c
> @@ -473,6 +473,9 @@ static int mxs_dcp_aes_enqueue(struct skcipher_request *req, int enc, int ecb)
>         struct dcp_aes_req_ctx *rctx = skcipher_request_ctx(req);
>         int ret;
>
> +       if (!req->cryptlen)
> +               return 0;
> +
>         if (unlikely(actx->key_len != AES_KEYSIZE_128 && !actx->key_referenced))
>                 return mxs_dcp_block_fallback(req, enc);
>
>
> base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
> --
> 2.25.1
>
>

Re: [PATCH] crypto: mxs-dcp: handle zero-length skcipher requests

[Linmao Li]

在 2026/8/29 3:25, Frank Li 写道:
> On Fri, Aug 28, 2026 at 05:32:09PM +0800, Linmao Li wrote:
>> [You don't often get email from lilinmao@kylinos.cn. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>>
>> Zero-length skcipher requests are valid no-ops, but MXS-DCP queues them.
> Any document show it? if return 0 when cryptelen, it is async, no
> call crypto_request_complete.
   Yes. CRYPTO_ALG_ASYNC means that the implementation may complete a
   request asynchronously, not that every request must do so.

   A return value of 0 indicates synchronous completion.  Only
   -EINPROGRESS and -EBUSY cause crypto_wait_req() to wait for the
   completion callback.  The existing fallback path relies on the same
   semantics.

   There is also a direct precedent in commit 8a4e047c6cc0
   ("crypto: marvell/cesa - Handle zero-length skcipher requests").
   Marvell CESA registers asynchronous skcipher algorithms but handles a
   zero-length request with:

           if (!req->cryptlen)
                   return 0;


Thanks,
Linmao

>
> Frank
>
>> When such a request reaches the worker, last_out_len remains zero. The
>> CBC completion path then subtracts AES_BLOCK_SIZE from this unsigned
>> value when updating the IV, causing the offset to underflow. On
>> decryption, the resulting source address precedes aes_in_buf.
>>
>> Return success before enqueueing zero-length requests. This avoids the
>> invalid source access and leaves the IV unchanged for a no-op.
>>
>> Fixes: fadd7a6e616b ("crypto: mxs-dcp - Fix AES issues")
>> Signed-off-by: Linmao Li <lilinmao@kylinos.cn>
>> ---
>>   drivers/crypto/mxs-dcp.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/crypto/mxs-dcp.c b/drivers/crypto/mxs-dcp.c
>> index 133ebc998236..60794b4d49fa 100644
>> --- a/drivers/crypto/mxs-dcp.c
>> +++ b/drivers/crypto/mxs-dcp.c
>> @@ -473,6 +473,9 @@ static int mxs_dcp_aes_enqueue(struct skcipher_request *req, int enc, int ecb)
>>          struct dcp_aes_req_ctx *rctx = skcipher_request_ctx(req);
>>          int ret;
>>
>> +       if (!req->cryptlen)
>> +               return 0;
>> +
>>          if (unlikely(actx->key_len != AES_KEYSIZE_128 && !actx->key_referenced))
>>                  return mxs_dcp_block_fallback(req, enc);
>>
>>
>> base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
>> --
>> 2.25.1
>>
>>

Re: [PATCH] crypto: mxs-dcp: handle zero-length skcipher requests

[Frank Li]

On Mon, Aug 31, 2026 at 08:42:20PM +0800, Linmao Li wrote:
> [You don't often get email from lilinmao@kylinos.cn. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>
> 在 2026/8/29 3:25, Frank Li 写道:
> > On Fri, Aug 28, 2026 at 05:32:09PM +0800, Linmao Li wrote:
> > > [You don't often get email from lilinmao@kylinos.cn. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> > >
> > > Zero-length skcipher requests are valid no-ops, but MXS-DCP queues them.
> > Any document show it? if return 0 when cryptelen, it is async, no
> > call crypto_request_complete.
>   Yes. CRYPTO_ALG_ASYNC means that the implementation may complete a
>   request asynchronously, not that every request must do so.
>
>   A return value of 0 indicates synchronous completion.  Only
>   -EINPROGRESS and -EBUSY cause crypto_wait_req() to wait for the
>   completion callback.  The existing fallback path relies on the same
>   semantics.
>
>   There is also a direct precedent in commit 8a4e047c6cc0
>   ("crypto: marvell/cesa - Handle zero-length skcipher requests").
>   Marvell CESA registers asynchronous skcipher algorithms but handles a
>   zero-length request with:
>
>           if (!req->cryptlen)
>                   return 0;

Thanks, but still not answer my question,

Any document show "Zero-length skcipher requests are valid no-ops", why
not API direct return 0, instead of pass to every driver to check it.

I suppose it should be checked before call driver's callback.

Frank

>
>
> Thanks,
> Linmao
>
> >
> > Frank
> >
> > > When such a request reaches the worker, last_out_len remains zero. The
> > > CBC completion path then subtracts AES_BLOCK_SIZE from this unsigned
> > > value when updating the IV, causing the offset to underflow. On
> > > decryption, the resulting source address precedes aes_in_buf.
> > >
> > > Return success before enqueueing zero-length requests. This avoids the
> > > invalid source access and leaves the IV unchanged for a no-op.
> > >
> > > Fixes: fadd7a6e616b ("crypto: mxs-dcp - Fix AES issues")
> > > Signed-off-by: Linmao Li <lilinmao@kylinos.cn>
> > > ---
> > >   drivers/crypto/mxs-dcp.c | 3 +++
> > >   1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/crypto/mxs-dcp.c b/drivers/crypto/mxs-dcp.c
> > > index 133ebc998236..60794b4d49fa 100644
> > > --- a/drivers/crypto/mxs-dcp.c
> > > +++ b/drivers/crypto/mxs-dcp.c
> > > @@ -473,6 +473,9 @@ static int mxs_dcp_aes_enqueue(struct skcipher_request *req, int enc, int ecb)
> > >          struct dcp_aes_req_ctx *rctx = skcipher_request_ctx(req);
> > >          int ret;
> > >
> > > +       if (!req->cryptlen)
> > > +               return 0;
> > > +
> > >          if (unlikely(actx->key_len != AES_KEYSIZE_128 && !actx->key_referenced))
> > >                  return mxs_dcp_block_fallback(req, enc);
> > >
> > >
> > > base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
> > > --
> > > 2.25.1
> > >
> > >

Re: [PATCH] crypto: mxs-dcp: handle zero-length skcipher requests

[Linmao Li]

在 2026/8/31 23:01, Frank Li 写道:
> On Mon, Aug 31, 2026 at 08:42:20PM +0800, Linmao Li wrote:
>> [You don't often get email from lilinmao@kylinos.cn. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>>
>> 在 2026/8/29 3:25, Frank Li 写道:
>>> On Fri, Aug 28, 2026 at 05:32:09PM +0800, Linmao Li wrote:
>>>> [You don't often get email from lilinmao@kylinos.cn. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>>>>
>>>> Zero-length skcipher requests are valid no-ops, but MXS-DCP queues them.
>>> Any document show it? if return 0 when cryptelen, it is async, no
>>> call crypto_request_complete.
>>    Yes. CRYPTO_ALG_ASYNC means that the implementation may complete a
>>    request asynchronously, not that every request must do so.
>>
>>    A return value of 0 indicates synchronous completion.  Only
>>    -EINPROGRESS and -EBUSY cause crypto_wait_req() to wait for the
>>    completion callback.  The existing fallback path relies on the same
>>    semantics.
>>
>>    There is also a direct precedent in commit 8a4e047c6cc0
>>    ("crypto: marvell/cesa - Handle zero-length skcipher requests").
>>    Marvell CESA registers asynchronous skcipher algorithms but handles a
>>    zero-length request with:
>>
>>            if (!req->cryptlen)
>>                    return 0;
> Thanks, but still not answer my question,
>
> Any document show "Zero-length skcipher requests are valid no-ops", why
> not API direct return 0, instead of pass to every driver to check it.
>
> I suppose it should be checked before call driver's callback.
   You are right; I could not find an explicit Crypto API document defining
   the zero-length behavior, so the wording "valid no-ops" was too broad.

   With the current API, simply returning 0 in the core for every
   zero-length request would change XTS semantics, since the generic XTS
   implementation returns -EINVAL.  MXS-DCP only implements ECB and CBC
   here, whose generic implementations currently return 0.  Handling it in
   the driver therefore matches existing behavior; centralizing this would
   require algorithm-specific length information.

   I agree that the commit message should describe this as existing ECB/CBC
   behavior rather than a general skcipher API rule.

   Thanks,
   Linmao
>
> Frank
>
>>
>> Thanks,
>> Linmao
>>
>>> Frank
>>>
>>>> When such a request reaches the worker, last_out_len remains zero. The
>>>> CBC completion path then subtracts AES_BLOCK_SIZE from this unsigned
>>>> value when updating the IV, causing the offset to underflow. On
>>>> decryption, the resulting source address precedes aes_in_buf.
>>>>
>>>> Return success before enqueueing zero-length requests. This avoids the
>>>> invalid source access and leaves the IV unchanged for a no-op.
>>>>
>>>> Fixes: fadd7a6e616b ("crypto: mxs-dcp - Fix AES issues")
>>>> Signed-off-by: Linmao Li <lilinmao@kylinos.cn>
>>>> ---
>>>>    drivers/crypto/mxs-dcp.c | 3 +++
>>>>    1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/drivers/crypto/mxs-dcp.c b/drivers/crypto/mxs-dcp.c
>>>> index 133ebc998236..60794b4d49fa 100644
>>>> --- a/drivers/crypto/mxs-dcp.c
>>>> +++ b/drivers/crypto/mxs-dcp.c
>>>> @@ -473,6 +473,9 @@ static int mxs_dcp_aes_enqueue(struct skcipher_request *req, int enc, int ecb)
>>>>           struct dcp_aes_req_ctx *rctx = skcipher_request_ctx(req);
>>>>           int ret;
>>>>
>>>> +       if (!req->cryptlen)
>>>> +               return 0;
>>>> +
>>>>           if (unlikely(actx->key_len != AES_KEYSIZE_128 && !actx->key_referenced))
>>>>                   return mxs_dcp_block_fallback(req, enc);
>>>>
>>>>
>>>> base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
>>>> --
>>>> 2.25.1
>>>>
>>>>

Re: [PATCH] crypto: mxs-dcp: handle zero-length skcipher requests

[Frank Li]

On Tue, Sep 01, 2026 at 11:05:30AM +0800, Linmao Li wrote:
>
> 在 2026/8/31 23:01, Frank Li 写道:
> > On Mon, Aug 31, 2026 at 08:42:20PM +0800, Linmao Li wrote:
> > > [You don't often get email from lilinmao@kylinos.cn. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> > >
> > > 在 2026/8/29 3:25, Frank Li 写道:
> > > > On Fri, Aug 28, 2026 at 05:32:09PM +0800, Linmao Li wrote:
> > > > > [You don't often get email from lilinmao@kylinos.cn. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> > > > >
> > > > > Zero-length skcipher requests are valid no-ops, but MXS-DCP queues them.
> > > > Any document show it? if return 0 when cryptelen, it is async, no
> > > > call crypto_request_complete.
> > >    Yes. CRYPTO_ALG_ASYNC means that the implementation may complete a
> > >    request asynchronously, not that every request must do so.
> > >
> > >    A return value of 0 indicates synchronous completion.  Only
> > >    -EINPROGRESS and -EBUSY cause crypto_wait_req() to wait for the
> > >    completion callback.  The existing fallback path relies on the same
> > >    semantics.
> > >
> > >    There is also a direct precedent in commit 8a4e047c6cc0
> > >    ("crypto: marvell/cesa - Handle zero-length skcipher requests").
> > >    Marvell CESA registers asynchronous skcipher algorithms but handles a
> > >    zero-length request with:
> > >
> > >            if (!req->cryptlen)
> > >                    return 0;
> > Thanks, but still not answer my question,
> >
> > Any document show "Zero-length skcipher requests are valid no-ops", why
> > not API direct return 0, instead of pass to every driver to check it.
> >
> > I suppose it should be checked before call driver's callback.
>   You are right; I could not find an explicit Crypto API document defining
>   the zero-length behavior, so the wording "valid no-ops" was too broad.
>
>   With the current API, simply returning 0 in the core for every
>   zero-length request would change XTS semantics, since the generic XTS
>   implementation returns -EINVAL.  MXS-DCP only implements ECB and CBC
>   here, whose generic implementations currently return 0.  Handling it in
>   the driver therefore matches existing behavior; centralizing this would
>   require algorithm-specific length information.
>
>   I agree that the commit message should describe this as existing ECB/CBC
>   behavior rather than a general skcipher API rule.

Okay

Frank
>
>   Thanks,
>   Linmao
> >
> > Frank
> >
> > >
> > > Thanks,
> > > Linmao
> > >
> > > > Frank
> > > >
> > > > > When such a request reaches the worker, last_out_len remains zero. The
> > > > > CBC completion path then subtracts AES_BLOCK_SIZE from this unsigned
> > > > > value when updating the IV, causing the offset to underflow. On
> > > > > decryption, the resulting source address precedes aes_in_buf.
> > > > >
> > > > > Return success before enqueueing zero-length requests. This avoids the
> > > > > invalid source access and leaves the IV unchanged for a no-op.
> > > > >
> > > > > Fixes: fadd7a6e616b ("crypto: mxs-dcp - Fix AES issues")
> > > > > Signed-off-by: Linmao Li <lilinmao@kylinos.cn>
> > > > > ---
> > > > >    drivers/crypto/mxs-dcp.c | 3 +++
> > > > >    1 file changed, 3 insertions(+)
> > > > >
> > > > > diff --git a/drivers/crypto/mxs-dcp.c b/drivers/crypto/mxs-dcp.c
> > > > > index 133ebc998236..60794b4d49fa 100644
> > > > > --- a/drivers/crypto/mxs-dcp.c
> > > > > +++ b/drivers/crypto/mxs-dcp.c
> > > > > @@ -473,6 +473,9 @@ static int mxs_dcp_aes_enqueue(struct skcipher_request *req, int enc, int ecb)
> > > > >           struct dcp_aes_req_ctx *rctx = skcipher_request_ctx(req);
> > > > >           int ret;
> > > > >
> > > > > +       if (!req->cryptlen)
> > > > > +               return 0;
> > > > > +
> > > > >           if (unlikely(actx->key_len != AES_KEYSIZE_128 && !actx->key_referenced))
> > > > >                   return mxs_dcp_block_fallback(req, enc);
> > > > >
> > > > >
> > > > > base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
> > > > > --
> > > > > 2.25.1
> > > > >
> > > > >