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

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Message-ID: <4af6c02f-db3f-3d82-9685-367913c684ff@maciej.szmigiero.name>
Date:   Sat, 24 Feb 2018 17:03:31 +0100
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>
Cc:     David Howells <dhowells@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Gary Hook <gary.hook@....com>, keyrings@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] crypto: ccp - protect RSA implementation from too large
 input data

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 <mail@...iej.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;
+	}
+
+	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