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SubjectRe: [PATCH] crypto: arm64/sm4 - Fix possible crash in GCM cryption
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Hi Herbert,

On 1/18/23 10:54 PM, Herbert Xu wrote:
> On Wed, Jan 18, 2023 at 10:19:28PM +0800, Tianjia Zhang wrote:
>> When the cryption total length is zero, GCM cryption call
>> skcipher_walk_done() will cause an unexpected crash, so skip calling
>> this function to avoid possible crash when the GCM cryption length
>> is equal to zero.
>>
>> Fixes: ae1b83c7d572 ("crypto: arm64/sm4 - add CE implementation for GCM mode")
>> Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
>> ---
>> arch/arm64/crypto/sm4-ce-gcm-glue.c | 12 +++++++-----
>> 1 file changed, 7 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/crypto/sm4-ce-gcm-glue.c b/arch/arm64/crypto/sm4-ce-gcm-glue.c
>> index c450a2025ca9..9b63bcf9aa85 100644
>> --- a/arch/arm64/crypto/sm4-ce-gcm-glue.c
>> +++ b/arch/arm64/crypto/sm4-ce-gcm-glue.c
>> @@ -178,11 +178,13 @@ static int gcm_crypt(struct aead_request *req, struct skcipher_walk *walk,
>>
>> kernel_neon_end();
>>
>> - err = skcipher_walk_done(walk, tail);
>> - if (err)
>> - return err;
>> - if (walk->nbytes)
>> - kernel_neon_begin();
>> + if (walk->nbytes) {
>
> Please do
> if (!walk->nbytes)
> break;

Thanks for the suggestion, a new patch has been sent.

>
> As an additional improvement, the tail calculation can be removed
> entirely because you already set the chunksize so the walker should
> only be feeding you multiples of chunksize except at the end.
>
> Cheers
I printed the walk->nbytes of each iteration of the walker, it is not
always multiples of chunksize except at the end when the algorithm test
manager is turned on.

For example, during a GCM encryption process, I get data like this:

total = 4014, nbytes = 2078, tail = 14
total = 1950, nbytes = 16, tail = 0
total = 1934, nbytes = 311, tail = 7
total = 1630, nbytes = 16, tail = 0
total = 1614, nbytes = 16, tail = 0
total = 1598, nbytes = 1598, tail = 14

Is my understanding wrong?

Best regards,
Tianjia

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