Clean up the check to make sure we can get the next header field.

Just check whether the pointer to it is within the available packet data
- and, if it's not, report truncation.

While we're at it:

Make the initialization vector length unsigned; it's either zero or a
positive number.

Rename a variable used for the ciphertext len to ctlen.

diff --git a/print-esp.c b/print-esp.c
index c743b764b9eac4b9ac7468428403cb05526852e7..ae6dc27bc5d60da588f4d346f7cc3a0863fa32d5 100644 (file)
--- a/print-esp.c
+++ b/print-esp.c
@@ -111,7 +111,7 @@ struct sa_list {
        u_char          spii[8];      /* for IKEv2 */
        u_char          spir[8];
        const EVP_CIPHER *evp;
-       int             ivlen;
+       u_int           ivlen;
        int             authlen;
        u_char          authsecret[256];
        int             authsecret_len;
@@ -406,6 +406,7 @@ espprint_decode_encalgo(netdissect_options *ndo,
 
        sa->evp = evp;
        sa->authlen = authlen;
+       /* This returns an int, but it should never be negative */
        sa->ivlen = EVP_CIPHER_iv_length(evp);
 
        colon++;
@@ -688,9 +689,9 @@ esp_print(netdissect_options *ndo,
        struct sa_list *sa = NULL;
        const struct ip6_hdr *ip6 = NULL;
        int advance;
-       int len;
+       u_int ctlen;
        u_char *secret;
-       int ivlen = 0;
+       u_int ivlen;
        const u_char *ivoff;
        const u_char *p;
        EVP_CIPHER_CTX *ctx;
@@ -745,7 +746,6 @@ esp_print(netdissect_options *ndo,
                        return;
                /* XXX - check whether it's fragmented? */
                /* if we can't get nexthdr, we do not need to decrypt it */
-               len = sizeof(struct ip6_hdr) + GET_BE_U_2(ip6->ip6_plen);
 
                /* see if we can find the SA, and if so, decode it */
                for (sa = ndo->ndo_sa_list_head; sa != NULL; sa = sa->next) {
@@ -761,7 +761,6 @@ esp_print(netdissect_options *ndo,
                /* nexthdr & padding are in the last fragment */
                if (fragmented)
                        return;
-               len = GET_BE_U_2(ip->ip_len);
 
                /* see if we can find the SA, and if so, decode it */
                for (sa = ndo->ndo_sa_list_head; sa != NULL; sa = sa->next) {
@@ -787,14 +786,6 @@ esp_print(netdissect_options *ndo,
        if (sa == NULL)
                return;
 
-       /* if we can't get nexthdr, we do not need to decrypt it */
-       if (ep - bp2 < len)
-               return;
-       if (ep - bp2 > len) {
-               /* FCS included at end of frame (NetBSD 1.6 or later) */
-               ep = bp2 + len;
-       }
-
        /* pointer to the IV, if there is one */
        ivoff = (const u_char *)(esp + 1) + 0;
        /* length of the IV, if there is one; 0, if there isn't */
@@ -805,12 +796,27 @@ esp_print(netdissect_options *ndo,
         * isn't bigger than the total amount of data available and, if
         * not, slice that off.
         */
-       if (ep - bp < sa->authlen)
+       if (ep - bp < sa->authlen) {
+               nd_print_trunc(ndo);
                return;
+       }
        ep = ep - sa->authlen;
 
        if (sa->evp == NULL)
                return;
+
+       /*
+        * If the next header value is past the end of the available
+        * data, we won't be able to fetch it once we've decrypted
+        * the ciphertext, so there's no point in decrypting the data.
+        *
+        * Report it as truncation.
+        */
+       if (!ND_TTEST_1(ep - 1)) {
+               nd_print_trunc(ndo);
+               return;
+       }
+
        ctx = EVP_CIPHER_CTX_new();
        if (ctx == NULL) {
                /*
@@ -834,7 +840,16 @@ esp_print(netdissect_options *ndo,
                (*ndo->ndo_warning)(ndo, "IV init failed");
                return;
        }
-       len = ep - (p + ivlen);
+
+       /*
+        * Calculate the length of the ciphertext.  ep points to
+        * the beginning of the authentication data/integrity check
+        * value, i.e. right past the end of the ciphertext; p points
+        * to the beginning of the payload, i.e. to the initialization
+        * vector, so if we skip past the initialization vector, it
+        * points to the beginning of the ciphertext.
+        */
+       ctlen = ep - (p + ivlen);
 
        /*
         * Allocate buffers for the encrypted and decrypted
@@ -843,7 +858,7 @@ esp_print(netdissect_options *ndo,
         * be separate from the input buffer.
         */
        block_size = (unsigned int)EVP_CIPHER_CTX_block_size(ctx);
-       buffer_size = len + (block_size - len % block_size);
+       buffer_size = ctlen + (block_size - ctlen % block_size);
 
        /*
         * Attempt to allocate the input buffer.
@@ -858,8 +873,8 @@ esp_print(netdissect_options *ndo,
         * Copy the input data to the encrypted data buffer,
         * and pad it with zeroes.
         */
-       memcpy(input_buffer, p + ivlen, len);
-       memset(input_buffer + len, 0, buffer_size - len);
+       memcpy(input_buffer, p + ivlen, ctlen);
+       memset(input_buffer + ctlen, 0, buffer_size - ctlen);
 
        /*
         * Attempt to allocate the output buffer.
@@ -872,7 +887,7 @@ esp_print(netdissect_options *ndo,
                        "esp_print: can't allocate memory for decryption buffer");
        }
 
-       if (!EVP_Cipher(ctx, output_buffer, input_buffer, len)) {
+       if (!EVP_Cipher(ctx, output_buffer, input_buffer, ctlen)) {
                free(input_buffer);
                (*ndo->ndo_warning)(ndo, "EVP_Cipher failed");
                return;
@@ -884,7 +899,7 @@ esp_print(netdissect_options *ndo,
         * const buffer, but changing this would require a
         * more complicated fix.
         */
-       memcpy(p + ivlen, output_buffer, len);
+       memcpy(p + ivlen, output_buffer, ctlen);
        free(output_buffer);
        advance = ivoff - (const u_char *)esp + ivlen;