digsig: remove unnecessary memory allocation and copying

In existing use case, copying of the decoded data is unnecessary in
pkcs_1_v1_5_decode_emsa. It is just enough to get pointer to the message.
Removing copying and extra buffer allocation.

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>

diff --git a/lib/digsig.c b/lib/digsig.c
index 8c0e629..0103c5b 100644 (file)
--- a/lib/digsig.c
+++ b/lib/digsig.c
@@ -30,11 +30,10 @@
 
 static struct crypto_shash *shash;
 
-static int pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
-                       unsigned long  msglen,
-                       unsigned long  modulus_bitlen,
-                       unsigned char *out,
-                       unsigned long *outlen)
+static const char *pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
+                                               unsigned long  msglen,
+                                               unsigned long  modulus_bitlen,
+                                               unsigned long *outlen)
 {
        unsigned long modulus_len, ps_len, i;
 
@@ -42,11 +41,11 @@ static int pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
 
        /* test message size */
        if ((msglen > modulus_len) || (modulus_len < 11))
-               return -EINVAL;
+               return NULL;
 
        /* separate encoded message */
-       if ((msg[0] != 0x00) || (msg[1] != (unsigned char)1))
-               return -EINVAL;
+       if (msg[0] != 0x00 || msg[1] != 0x01)
+               return NULL;
 
        for (i = 2; i < modulus_len - 1; i++)
                if (msg[i] != 0xFF)
@@ -56,19 +55,13 @@ static int pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
        if (msg[i] != 0)
                /* There was no octet with hexadecimal value 0x00
                to separate ps from m. */
-               return -EINVAL;
+               return NULL;
 
        ps_len = i - 2;
 
-       if (*outlen < (msglen - (2 + ps_len + 1))) {
-               *outlen = msglen - (2 + ps_len + 1);
-               return -EOVERFLOW;
-       }
-
        *outlen = (msglen - (2 + ps_len + 1));
-       memcpy(out, &msg[2 + ps_len + 1], *outlen);
 
-       return 0;
+       return msg + 2 + ps_len + 1;
 }
 
 /*
@@ -83,7 +76,8 @@ static int digsig_verify_rsa(struct key *key,
        unsigned long mlen, mblen;
        unsigned nret, l;
        int head, i;
-       unsigned char *out1 = NULL, *out2 = NULL;
+       unsigned char *out1 = NULL;
+       const char *m;
        MPI in = NULL, res = NULL, pkey[2];
        uint8_t *p, *datap, *endp;
        struct user_key_payload *ukp;
@@ -120,7 +114,7 @@ static int digsig_verify_rsa(struct key *key,
        }
 
        mblen = mpi_get_nbits(pkey[0]);
-       mlen = (mblen + 7)/8;
+       mlen = DIV_ROUND_UP(mblen, 8);
 
        if (mlen == 0)
                goto err;
@@ -129,10 +123,6 @@ static int digsig_verify_rsa(struct key *key,
        if (!out1)
                goto err;
 
-       out2 = kzalloc(mlen, GFP_KERNEL);
-       if (!out2)
-               goto err;
-
        nret = siglen;
        in = mpi_read_from_buffer(sig, &nret);
        if (!in)
@@ -162,18 +152,15 @@ static int digsig_verify_rsa(struct key *key,
        memset(out1, 0, head);
        memcpy(out1 + head, p, l);
 
-       err = pkcs_1_v1_5_decode_emsa(out1, len, mblen, out2, &len);
-       if (err)
-               goto err;
+       m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
 
-       if (len != hlen || memcmp(out2, h, hlen))
+       if (!m || len != hlen || memcmp(m, h, hlen))
                err = -EINVAL;
 
 err:
        mpi_free(in);
        mpi_free(res);
        kfree(out1);
-       kfree(out2);
        while (--i >= 0)
                mpi_free(pkey[i]);
 err1: