Avoid passing null pointers to memcpy/memcmp

By a strict reading of the C standard, memcpy and memcmp have
undefined behavior if their pointer arguments aren't valid object
pointers, even if the length argument is 0.  Compilers are becoming
more aggressive about breaking code with undefined behavior, so we
should try to avoid it when possible.

In a krb5_data object, we frequently use NULL as the data value when
the length is 0.  Accordingly, we should avoid copying from or
comparing the data field of a length-0 krb5_data object.  Add checks
to our wrapper functions (like data_eq and k5_memdup) and to code
which works with possibly-empty krb5_data objects.  In a few places,
use wrapper functions to simplify the code rather than adding checks.

21 files changed, 76 insertions, 65 deletions

diff --git a/src/include/k5-int.h b/src/include/k5-int.h
index d804047598..a489ce3839 100644
--- a/src/include/k5-int.h
+++ b/src/include/k5-int.h
@@ -2138,13 +2138,15 @@ krb5_error_code krb5_set_time_offsets(krb5_context, krb5_timestamp,
 static inline int
 data_eq(krb5_data d1, krb5_data d2)
 {
-    return (d1.length == d2.length && !memcmp(d1.data, d2.data, d1.length));
+    return (d1.length == d2.length && (d1.length == 0 ||
+                                       !memcmp(d1.data, d2.data, d1.length)));
 }
 
 static inline int
 data_eq_string (krb5_data d, const char *s)
 {
-    return (d.length == strlen(s) && !memcmp(d.data, s, d.length));
+    return (d.length == strlen(s) && (d.length == 0 ||
+                                      !memcmp(d.data, s, d.length)));
 }
 
 static inline krb5_data
@@ -2187,9 +2189,8 @@ alloc_data(krb5_data *data, unsigned int len)
 static inline int
 authdata_eq(krb5_authdata a1, krb5_authdata a2)
 {
-    return (a1.ad_type == a2.ad_type
-            && a1.length == a2.length
-            && !memcmp(a1.contents, a2.contents, a1.length));
+    return (a1.ad_type == a2.ad_type && a1.length == a2.length &&
+            (a1.length == 0 || !memcmp(a1.contents, a2.contents, a1.length)));
 }
 
 /* Allocate zeroed memory; set *code to 0 on success or ENOMEM on failure. */
@@ -2210,7 +2211,7 @@ k5memdup(const void *in, size_t len, krb5_error_code *code)
 {
     void *ptr = k5alloc(len, code);
 
-    if (ptr != NULL)
+    if (ptr != NULL && len > 0)
         memcpy(ptr, in, len);
     return ptr;
 }
@@ -2221,7 +2222,7 @@ k5memdup0(const void *in, size_t len, krb5_error_code *code)
 {
     void *ptr = k5alloc(len + 1, code);
 
-    if (ptr != NULL)
+    if (ptr != NULL && len > 0)
         memcpy(ptr, in, len);
     return ptr;
 }
diff --git a/src/kdc/kdc_transit.c b/src/kdc/kdc_transit.c
index 9947761450..c540ad26cb 100644
--- a/src/kdc/kdc_transit.c
+++ b/src/kdc/kdc_transit.c
@@ -135,7 +135,8 @@ data2string (krb5_data *d)
     char *s;
     s = malloc(d->length + 1);
     if (s) {
-        memcpy(s, d->data, d->length);
+        if (d->length > 0)
+            memcpy(s, d->data, d->length);
         s[d->length] = 0;
     }
     return s;
diff --git a/src/kdc/kdc_util.c b/src/kdc/kdc_util.c
index 4e85f68753..9948e1bbe3 100644
--- a/src/kdc/kdc_util.c
+++ b/src/kdc/kdc_util.c
@@ -1091,16 +1091,21 @@ verify_for_user_checksum(krb5_context context,
     p += 4;
 
     for (i = 0; i < krb5_princ_size(context, req->user); i++) {
-        memcpy(p, krb5_princ_component(context, req->user, i)->data,
-               krb5_princ_component(context, req->user, i)->length);
+        if (krb5_princ_component(context, req->user, i)->length > 0) {
+            memcpy(p, krb5_princ_component(context, req->user, i)->data,
+                   krb5_princ_component(context, req->user, i)->length);
+        }
         p += krb5_princ_component(context, req->user, i)->length;
     }
 
-    memcpy(p, krb5_princ_realm(context, req->user)->data,
-           krb5_princ_realm(context, req->user)->length);
+    if (krb5_princ_realm(context, req->user)->length > 0) {
+        memcpy(p, krb5_princ_realm(context, req->user)->data,
+               krb5_princ_realm(context, req->user)->length);
+    }
     p += krb5_princ_realm(context, req->user)->length;
 
-    memcpy(p, req->auth_package.data, req->auth_package.length);
+    if (req->auth_package.length > 0)
+        memcpy(p, req->auth_package.data, req->auth_package.length);
     p += req->auth_package.length;
 
     code = krb5_c_verify_checksum(context,
diff --git a/src/lib/crypto/krb/encrypt.c b/src/lib/crypto/krb/encrypt.c
index f46fb1370f..d9d575a4dd 100644
--- a/src/lib/crypto/krb/encrypt.c
+++ b/src/lib/crypto/krb/encrypt.c
@@ -60,7 +60,8 @@ krb5_k_encrypt(krb5_context context, krb5_key key,
     iov[1].flags = KRB5_CRYPTO_TYPE_DATA;
     iov[1].data = make_data(output->ciphertext.data + header_len,
                             input->length);
-    memcpy(iov[1].data.data, input->data, input->length);
+    if (input->length > 0)
+        memcpy(iov[1].data.data, input->data, input->length);
 
     iov[2].flags = KRB5_CRYPTO_TYPE_PADDING;
     iov[2].data = make_data(iov[1].data.data + input->length, padding_len);
diff --git a/src/lib/crypto/krb/s2k_des.c b/src/lib/crypto/krb/s2k_des.c
index 61b3c0f012..31a613bebc 100644
--- a/src/lib/crypto/krb/s2k_des.c
+++ b/src/lib/crypto/krb/s2k_des.c
@@ -404,7 +404,8 @@ afs_s2k_oneblock(const krb5_data *data, const krb5_data *salt,
      */
 
     memset(password, 0, sizeof(password));
-    memcpy(password, salt->data, min(salt->length, 8));
+    if (salt->length > 0)
+        memcpy(password, salt->data, min(salt->length, 8));
     for (i = 0; i < 8; i++) {
         if (isupper(password[i]))
             password[i] = tolower(password[i]);
@@ -443,7 +444,8 @@ afs_s2k_multiblock(const krb5_data *data, const krb5_data *salt,
     if (!password)
         return ENOMEM;
 
-    memcpy(password, data->data, data->length);
+    if (data->length > 0)
+        memcpy(password, data->data, data->length);
     for (i = data->length, j = 0; j < salt->length; i++, j++) {
         password[i] = salt->data[j];
         if (isupper(password[i]))
@@ -513,8 +515,9 @@ des_s2k(const krb5_data *pw, const krb5_data *salt, unsigned char *key_out)
     copy = malloc(copylen);
     if (copy == NULL)
         return ENOMEM;
-    memcpy(copy, pw->data, pw->length);
-    if (salt)
+    if (pw->length > 0)
+        memcpy(copy, pw->data, pw->length);
+    if (salt != NULL && salt->length > 0)
         memcpy(copy + pw->length, salt->data, salt->length);
 
     memset(&temp, 0, sizeof(temp));
diff --git a/src/lib/crypto/krb/s2k_pbkdf2.c b/src/lib/crypto/krb/s2k_pbkdf2.c
index 2476865f35..4ada811ec0 100644
--- a/src/lib/crypto/krb/s2k_pbkdf2.c
+++ b/src/lib/crypto/krb/s2k_pbkdf2.c
@@ -61,8 +61,9 @@ krb5int_dk_string_to_key(const struct krb5_keytypes *ktp,
 
     /* construct input string ( = string + salt), fold it, make_key it */
 
-    memcpy(concat, string->data, string->length);
-    if (salt)
+    if (string->length > 0)
+        memcpy(concat, string->data, string->length);
+    if (salt != NULL && salt->length > 0)
         memcpy(concat + string->length, salt->data, salt->length);
 
     krb5int_nfold(concatlen*8, concat, keybytes*8, foldstring);
@@ -146,9 +147,11 @@ pbkdf2_string_to_key(const struct krb5_keytypes *ktp, const krb5_data *string,
         if (err)
             return err;
 
-        memcpy(sandp.data, pepper->data, pepper->length);
+        if (pepper->length > 0)
+            memcpy(sandp.data, pepper->data, pepper->length);
         sandp.data[pepper->length] = '\0';
-        memcpy(&sandp.data[pepper->length + 1], salt->data, salt->length);
+        if (salt->length > 0)
+            memcpy(&sandp.data[pepper->length + 1], salt->data, salt->length);
 
         salt = &sandp;
     }
diff --git a/src/lib/gssapi/krb5/iakerb.c b/src/lib/gssapi/krb5/iakerb.c
index 8c6a0823f1..f30de324aa 100644
--- a/src/lib/gssapi/krb5/iakerb.c
+++ b/src/lib/gssapi/krb5/iakerb.c
@@ -278,7 +278,8 @@ iakerb_make_token(iakerb_ctx_id_t ctx,
     }
     data->data = p;
 
-    memcpy(data->data + data->length, request->data, request->length);
+    if (request->length > 0)
+        memcpy(data->data + data->length, request->data, request->length);
     data->length += request->length;
 
     if (initialContextToken)
diff --git a/src/lib/krb5/ccache/ccfns.c b/src/lib/krb5/ccache/ccfns.c
index 3154b17c8f..1a0bed0acd 100644
--- a/src/lib/krb5/ccache/ccfns.c
+++ b/src/lib/krb5/ccache/ccfns.c
@@ -284,15 +284,9 @@ krb5_cc_set_config(krb5_context context, krb5_ccache id,
     if (data == NULL) {
         ret = krb5_cc_remove_cred(context, id, 0, &cred);
     } else {
-        cred.ticket.data = malloc(data->length);
-        if (cred.ticket.data == NULL) {
-            ret = ENOMEM;
-            krb5_set_error_message(context, ret, "malloc: out of memory");
+        ret = krb5int_copy_data_contents(context, data, &cred.ticket);
+        if (ret)
             goto out;
-        }
-        cred.ticket.length = data->length;
-        memcpy(cred.ticket.data, data->data, data->length);
-
         ret = krb5_cc_store_cred(context, id, &cred);
     }
 out:
@@ -319,14 +313,9 @@ krb5_cc_get_config(krb5_context context, krb5_ccache id,
     if (ret)
         goto out;
 
-    data->data = malloc(cred.ticket.length);
-    if (data->data == NULL) {
-        ret = ENOMEM;
-        krb5_set_error_message(context, ENOMEM, "malloc: out of memory");
+    ret = krb5int_copy_data_contents(context, &cred.ticket, data);
+    if (ret)
         goto out;
-    }
-    data->length = cred.ticket.length;
-    memcpy(data->data, cred.ticket.data, data->length);
 
     TRACE_CC_GET_CONFIG(context, id, principal, key, data);
 
diff --git a/src/lib/krb5/ccache/ccselect_k5identity.c b/src/lib/krb5/ccache/ccselect_k5identity.c
index adf0fad269..bee5416587 100644
--- a/src/lib/krb5/ccache/ccselect_k5identity.c
+++ b/src/lib/krb5/ccache/ccselect_k5identity.c
@@ -46,14 +46,13 @@ k5identity_init(krb5_context context, krb5_ccselect_moddata *data_out,
 static krb5_boolean
 fnmatch_data(const char *pattern, krb5_data *data, krb5_boolean fold_case)
 {
+    krb5_error_code ret;
     char *str, *p;
     int res;
 
-    str = malloc(data->length + 1);
+    str = k5memdup0(data->data, data->length, &ret);
     if (str == NULL)
         return FALSE;
-    memcpy(str, data->data, data->length);
-    str[data->length] = '\0';
 
     if (fold_case) {
         for (p = str; *p != '\0'; p++) {
diff --git a/src/lib/krb5/krb/authdata.c b/src/lib/krb5/krb/authdata.c
index 546fb82dc5..75b1c6ec0f 100644
--- a/src/lib/krb5/krb/authdata.c
+++ b/src/lib/krb5/krb/authdata.c
@@ -292,8 +292,7 @@ k5_ad_find_module(krb5_context kcontext,
             continue;
 
         /* check for name match */
-        if (strlen(module->name) != name->length ||
-            memcmp(module->name, name->data, name->length) != 0)
+        if (!data_eq_string(*name, module->name))
             continue;
 
         ret = module;
diff --git a/src/lib/krb5/krb/chk_trans.c b/src/lib/krb5/krb/chk_trans.c
index 2c29e62c61..71833e6095 100644
--- a/src/lib/krb5/krb/chk_trans.c
+++ b/src/lib/krb5/krb/chk_trans.c
@@ -242,7 +242,8 @@ foreach_realm (krb5_error_code (*fn)(krb5_data *comp,void *data), void *data,
                 if (p == transit->data) {
                     if (crealm->length >= MAXLEN)
                         return KRB5KRB_AP_ERR_ILL_CR_TKT;
-                    memcpy (last, crealm->data, crealm->length);
+                    if (crealm->length > 0)
+                        memcpy (last, crealm->data, crealm->length);
                     last[crealm->length] = '\0';
                     last_component.length = crealm->length;
                 }
diff --git a/src/lib/krb5/krb/conv_princ.c b/src/lib/krb5/krb/conv_princ.c
index 04d4b6514a..c33c67dda5 100644
--- a/src/lib/krb5/krb/conv_princ.c
+++ b/src/lib/krb5/krb/conv_princ.c
@@ -194,7 +194,8 @@ krb5_524_conv_principal(krb5_context context, krb5_const_principal princ,
             compo = &princ->data[1];
             if (compo->length >= INST_SZ - 1)
                 return KRB5_INVALID_PRINCIPAL;
-            memcpy(inst, compo->data, compo->length);
+            if (compo->length > 0)
+                memcpy(inst, compo->data, compo->length);
             inst[compo->length] = '\0';
         }
         /* fall through */
@@ -204,7 +205,8 @@ krb5_524_conv_principal(krb5_context context, krb5_const_principal princ,
             compo = &princ->data[0];
             if (compo->length >= ANAME_SZ)
                 return KRB5_INVALID_PRINCIPAL;
-            memcpy(name, compo->data, compo->length);
+            if (compo->length > 0)
+                memcpy(name, compo->data, compo->length);
             name[compo->length] = '\0';
         }
         break;
diff --git a/src/lib/krb5/krb/get_in_tkt.c b/src/lib/krb5/krb/get_in_tkt.c
index 15f7cc6dc6..59614e7135 100644
--- a/src/lib/krb5/krb/get_in_tkt.c
+++ b/src/lib/krb5/krb/get_in_tkt.c
@@ -1073,6 +1073,7 @@ init_creds_validate_reply(krb5_context context,
 static void
 read_allowed_preauth_type(krb5_context context, krb5_init_creds_context ctx)
 {
+    krb5_error_code ret;
     krb5_data config;
     char *tmp, *p;
 
@@ -1084,18 +1085,14 @@ read_allowed_preauth_type(krb5_context context, krb5_init_creds_context ctx)
                            ctx->request->server,
                            KRB5_CC_CONF_PA_TYPE, &config) != 0)
         return;
-    tmp = malloc(config.length + 1);
-    if (tmp == NULL) {
-        krb5_free_data_contents(context, &config);
+    tmp = k5memdup0(config.data, config.length, &ret);
+    krb5_free_data_contents(context, &config);
+    if (tmp == NULL)
         return;
-    }
-    memcpy(tmp, config.data, config.length);
-    tmp[config.length] = '\0';
     ctx->allowed_preauth_type = strtol(tmp, &p, 10);
     if (p == NULL || *p != '\0')
         ctx->allowed_preauth_type = KRB5_PADATA_NONE;
     free(tmp);
-    krb5_free_data_contents(context, &config);
 }
 
 static krb5_error_code
diff --git a/src/lib/krb5/krb/pr_to_salt.c b/src/lib/krb5/krb/pr_to_salt.c
index 87fe91117f..00d0c734f9 100644
--- a/src/lib/krb5/krb/pr_to_salt.c
+++ b/src/lib/krb5/krb/pr_to_salt.c
@@ -56,11 +56,13 @@ principal2salt_internal(krb5_context context,
 
     if (use_realm) {
         offset = pr->realm.length;
-        memcpy(ret->data, pr->realm.data, offset);
+        if (offset > 0)
+            memcpy(ret->data, pr->realm.data, offset);
     }
 
     for (i = 0; i < pr->length; i++) {
-        memcpy(&ret->data[offset], pr->data[i].data, pr->data[i].length);
+        if (pr->data[i].length > 0)
+            memcpy(&ret->data[offset], pr->data[i].data, pr->data[i].length);
         offset += pr->data[i].length;
     }
     return 0;
diff --git a/src/lib/krb5/krb/princ_comp.c b/src/lib/krb5/krb/princ_comp.c
index 994f41d45c..a6936107de 100644
--- a/src/lib/krb5/krb/princ_comp.c
+++ b/src/lib/krb5/krb/princ_comp.c
@@ -38,6 +38,8 @@ realm_compare_flags(krb5_context context,
 
     if (realm1->length != realm2->length)
         return FALSE;
+    if (realm1->length == 0)
+        return TRUE;
 
     return (flags & KRB5_PRINCIPAL_COMPARE_CASEFOLD) ?
         (strncasecmp(realm1->data, realm2->data, realm2->length) == 0) :
diff --git a/src/lib/krb5/krb/s4u_creds.c b/src/lib/krb5/krb/s4u_creds.c
index b7bb9fe5b0..c85c0d44a3 100644
--- a/src/lib/krb5/krb/s4u_creds.c
+++ b/src/lib/krb5/krb/s4u_creds.c
@@ -161,14 +161,17 @@ make_pa_for_user_checksum(krb5_context context,
     p += 4;
 
     for (i = 0; i < req->user->length; i++) {
-        memcpy(p, req->user->data[i].data, req->user->data[i].length);
+        if (req->user->data[i].length > 0)
+            memcpy(p, req->user->data[i].data, req->user->data[i].length);
         p += req->user->data[i].length;
     }
 
-    memcpy(p, req->user->realm.data, req->user->realm.length);
+    if (req->user->realm.length > 0)
+        memcpy(p, req->user->realm.data, req->user->realm.length);
     p += req->user->realm.length;
 
-    memcpy(p, req->auth_package.data, req->auth_package.length);
+    if (req->auth_package.length > 0)
+        memcpy(p, req->auth_package.data, req->auth_package.length);
 
     /* Per spec, use hmac-md5 checksum regardless of key type. */
     code = krb5_c_make_checksum(context, CKSUMTYPE_HMAC_MD5_ARCFOUR, key,
diff --git a/src/lib/krb5/krb/unparse.c b/src/lib/krb5/krb/unparse.c
index 779121a860..5bb64d00ad 100644
--- a/src/lib/krb5/krb/unparse.c
+++ b/src/lib/krb5/krb/unparse.c
@@ -90,7 +90,8 @@ copy_component_quoting(char *dest, const krb5_data *src, int flags)
     int length = src->length;
 
     if (flags & KRB5_PRINCIPAL_UNPARSE_DISPLAY) {
-        memcpy(dest, src->data, src->length);
+        if (src->length > 0)
+            memcpy(dest, src->data, src->length);
         return src->length;
     }
 
diff --git a/src/lib/krb5/krb/walk_rtree.c b/src/lib/krb5/krb/walk_rtree.c
index 0aed147f34..2b966287c4 100644
--- a/src/lib/krb5/krb/walk_rtree.c
+++ b/src/lib/krb5/krb/walk_rtree.c
@@ -105,10 +105,8 @@ krb5_walk_realm_tree( krb5_context context,
     if (client->data == NULL || server->data == NULL)
         return KRB5_NO_TKT_IN_RLM;
 
-    if (client->length == server->length &&
-        memcmp(client->data, server->data, server->length) == 0) {
+    if (data_eq(*client, *server))
         return KRB5_NO_TKT_IN_RLM;
-    }
     retval = rtree_capath_vals(context, client, server, &capvals);
     if (retval)
         return retval;
diff --git a/src/plugins/preauth/securid_sam2/securid2.c b/src/plugins/preauth/securid_sam2/securid2.c
index 57d4e37d20..e3c8c7dae2 100644
--- a/src/plugins/preauth/securid_sam2/securid2.c
+++ b/src/plugins/preauth/securid_sam2/securid2.c
@@ -378,7 +378,8 @@ verify_securid_data_2(krb5_context context, krb5_db_entry *client,
                 esre2->sam_sad.length, user);
         goto cleanup;
     }
-    memcpy(passcode, esre2->sam_sad.data, esre2->sam_sad.length);
+    if (esre2->sam_sad.length > 0)
+        memcpy(passcode, esre2->sam_sad.data, esre2->sam_sad.length);
 
     securid_user = strdup(user);
     if (!securid_user) {
diff --git a/src/util/support/json.c b/src/util/support/json.c
index c7f6fdd4a9..b2dd1333e7 100644
--- a/src/util/support/json.c
+++ b/src/util/support/json.c
@@ -489,7 +489,8 @@ k5_json_string_create_len(const void *data, size_t len,
     s = alloc_value(&string_type, len + 1);
     if (s == NULL)
         return ENOMEM;
-    memcpy(s, data, len);
+    if (len > 0)
+        memcpy(s, data, len);
     s[len] = '\0';
     *val_out = (k5_json_string)s;
     return 0;
diff --git a/src/util/support/k5buf.c b/src/util/support/k5buf.c
index 7d491ce2bd..778e68b39b 100644
--- a/src/util/support/k5buf.c
+++ b/src/util/support/k5buf.c
@@ -119,7 +119,8 @@ k5_buf_add_len(struct k5buf *buf, const char *data, size_t len)
 {
     if (!ensure_space(buf, len))
         return;
-    memcpy(buf->data + buf->len, data, len);
+    if (len > 0)
+        memcpy(buf->data + buf->len, data, len);
     buf->len += len;
     buf->data[buf->len] = '\0';
 }