Re: [PATCH 3/3] crypto: ccp - protect RSA implementation from too large input data

[Gary R Hook]

On 02/24/2018 10:03 AM, Maciej S. Szmigiero wrote:
CCP RSA implementation uses a hardware input buffer which size depends only
on the current RSA key length. Key modulus and a message to be processed
is then copied to this buffer based on their own lengths.
Since the price for providing too long input data is a buffer overflow and
there already has been a case when this has happened let's better reject
such oversized input data and log an error message in this case so we know
what is going on.

Signed-off-by: Maciej S. Szmigiero <m...@maciej.szmigiero.name>
---
  drivers/crypto/ccp/ccp-ops.c | 24 ++++++++++++++++++++----
  1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/drivers/crypto/ccp/ccp-ops.c b/drivers/crypto/ccp/ccp-ops.c
index 406b95329b3d..517aeee30abf 100644
--- a/drivers/crypto/ccp/ccp-ops.c
+++ b/drivers/crypto/ccp/ccp-ops.c
@@ -1770,10 +1770,6 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue *cmd_q, 
struct ccp_cmd *cmd)
        if (!rsa->exp || !rsa->mod || !rsa->src || !rsa->dst)
                return -EINVAL;
  
-	memset(&op, 0, sizeof(op));
-       op.cmd_q = cmd_q;
-       op.jobid = CCP_NEW_JOBID(cmd_q->ccp);
-
        /* The RSA modulus must precede the message being acted upon, so
         * it must be copied to a DMA area where the message and the
         * modulus can be concatenated.  Therefore the input buffer
@@ -1785,6 +1781,26 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue *cmd_q, 
struct ccp_cmd *cmd)
        o_len = 32 * ((rsa->key_size + 255) / 256);
        i_len = o_len * 2;
  
+	if (rsa->mod_len > o_len) {
+               dev_err(cmd_q->ccp->dev,
+                       "RSA modulus of %u bytes too large for key size of %u 
bits\n",
+                       (unsigned int)rsa->mod_len,
+                       (unsigned int)rsa->key_size);
+               return -EINVAL;
+       }
+
+       if (rsa->src_len > o_len) {
+               dev_err(cmd_q->ccp->dev,
+                       "RSA data of %u bytes too large for key size of %u 
bits\n",
+                       (unsigned int)rsa->src_len,
+                       (unsigned int)rsa->key_size);
+               return -EINVAL;
+       }

We've talked about this, and we believe that a more central fix is 
warranted. I intend to post another patch tomorrow that should address
this problem.

+
+       memset(&op, 0, sizeof(op));
+       op.cmd_q = cmd_q;
+       op.jobid = CCP_NEW_JOBID(cmd_q->ccp);
+
        sb_count = 0;
        if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0)) {
                /* sb_count is the number of storage block slots required