Change in libosmo-pfcp[master]: gtlv: check memory bounds 1/3: encoding TLV

neels has uploaded this change for review. ( https://gerrit.osmocom.org/c/libosmo-pfcp/+/29039 ) Change subject: gtlv: check memory bounds 1/3: encoding TLV ...................................................................... gtlv: check memory bounds 1/3: encoding TLV Introduce a maximum bound of memory access to the osmo_gtlv API. Properly pass const-ness within the gtlv implementation. This patch adds membof_const(). The following patch will add the non-const membof() equivalent, which is not needed in this patch, yet. Coverity CID#275417 drew my attention to the fact that the gtlv decoding and encoding does not actually guard against access past the end of the decoded struct. We have not yet officially released libosmo-gtlv; also, osmo-upf and osmo-hnbgw so far only use the libosmo-pfcp API, which "hides" the gtlv API. Hence just change the API without a backwards compat shim. Related: CID#275417 Change-Id: Id8d997c9d5e655ff1842ec69eab6c073875c6330 --- M include/osmocom/gtlv/gtlv_dec_enc.h M src/libosmo-gtlv/gtlv_dec_enc.c M src/libosmo-gtlv/gtlv_gen.c M tests/libosmo-gtlv/gtlv_dec_enc_test.c 4 files changed, 29 insertions(+), 14 deletions(-) git pull ssh://gerrit.osmocom.org:29418/libosmo-pfcp refs/changes/39/29039/1 diff --git a/include/osmocom/gtlv/gtlv_dec_enc.h b/include/osmocom/gtlv/gtlv_dec_enc.h index 132239f..df8d161 100644 --- a/include/osmocom/gtlv/gtlv_dec_enc.h +++ b/include/osmocom/gtlv/gtlv_dec_enc.h @@ -186,9 +186,9 @@ const struct osmo_gtlv_coding *ie_coding, osmo_gtlv_err_cb err_cb, void *err_cb_data, const struct value_string *iei_strs); -int osmo_gtlvs_encode(struct osmo_gtlv_put *gtlv, const void *decoded_struct, unsigned int obj_ofs, - const struct osmo_gtlv_coding *ie_coding, - osmo_gtlv_err_cb err_cb, void *err_cb_data, const struct value_string *iei_strs); +int osmo_gtlvs_encode(struct osmo_gtlv_put *gtlv, const void *decoded_struct, size_t decoded_struct_max_len, + unsigned int obj_ofs, const struct osmo_gtlv_coding *ie_coding, osmo_gtlv_err_cb err_cb, + void *err_cb_data, const struct value_string *iei_strs); int osmo_gtlvs_encode_to_str_buf(char *buf, size_t buflen, const void *decoded_struct, unsigned int obj_ofs, const struct osmo_gtlv_coding *ie_coding, const struct value_string *iei_strs); diff --git a/src/libosmo-gtlv/gtlv_dec_enc.c b/src/libosmo-gtlv/gtlv_dec_enc.c index 2e5509a..f60ea94 100644 --- a/src/libosmo-gtlv/gtlv_dec_enc.c +++ b/src/libosmo-gtlv/gtlv_dec_enc.c @@ -49,6 +49,15 @@ return RC; \ } while (0) +/* Reverse offsetof(): return the address of the struct member for a given osmo_gtlv_msg and member ofs_foo value. */ +static const void *membof_const(const void *parent, size_t parent_max_len, unsigned int memb_ofs) +{ + const char *p = parent; + const char *end = p + parent_max_len; + const char *memb = p + memb_ofs; + OSMO_ASSERT(memb < end); + return memb; +} /*! Decode a TLV structure from raw data to a decoded struct, for unordered TLV IEs. * How to decode IE values and where to place them in the decoded struct, is defined by ie_coding, an array terminated @@ -378,19 +387,22 @@ * \param[in] iei_strs value_string array to give IEI names in error messages passed to err_cb(), or NULL. * \return 0 on success, negative on error. */ -int osmo_gtlvs_encode(struct osmo_gtlv_put *gtlv, const void *decoded_struct, unsigned int obj_ofs, - const struct osmo_gtlv_coding *ie_coding, - osmo_gtlv_err_cb err_cb, void *err_cb_data, const struct value_string *iei_strs) +int osmo_gtlvs_encode(struct osmo_gtlv_put *gtlv, const void *decoded_struct, size_t decoded_struct_max_len, + unsigned int obj_ofs, const struct osmo_gtlv_coding *ie_coding, osmo_gtlv_err_cb err_cb, + void *err_cb_data, const struct value_string *iei_strs) { - void *obj = MEMB(decoded_struct, obj_ofs); + const void *obj = membof_const(decoded_struct, decoded_struct_max_len, obj_ofs); + size_t obj_maxlen = decoded_struct_max_len - obj_ofs; if (!ie_coding) return -ENOTSUP; for (; !osmo_gtlv_coding_end(ie_coding); ie_coding++) { int rc; - bool *presence_flag_p = ie_coding->has_presence_flag ? MEMB(obj, ie_coding->presence_flag_ofs) : NULL; - unsigned int *multi_count_p = ie_coding->has_count ? MEMB(obj, ie_coding->count_ofs) : NULL; + const bool *presence_flag_p = ie_coding->has_presence_flag ? + membof_const(obj, obj_maxlen, ie_coding->presence_flag_ofs) : NULL; + const unsigned int *multi_count_p = ie_coding->has_count ? + membof_const(obj, obj_maxlen, ie_coding->count_ofs) : NULL; unsigned int n; unsigned int i; @@ -423,13 +435,14 @@ .cfg = ie_coding->nested_ies_cfg ? : gtlv->cfg, .dst = gtlv->dst, }; - rc = osmo_gtlvs_encode(&nested_tlv, decoded_struct, obj_ofs + memb_ofs, - ie_coding->nested_ies, err_cb, err_cb_data, iei_strs); + rc = osmo_gtlvs_encode(&nested_tlv, decoded_struct, decoded_struct_max_len, + obj_ofs + memb_ofs, ie_coding->nested_ies, + err_cb, err_cb_data, iei_strs); if (rc) RETURN_ERROR(rc, ie_coding->ti, "Error while encoding TLV structure nested inside this IE"); } else { - rc = ie_coding->enc_func(gtlv, decoded_struct, MEMB(obj, memb_ofs)); + rc = ie_coding->enc_func(gtlv, decoded_struct, membof_const(obj, obj_maxlen, memb_ofs)); if (rc) RETURN_ERROR(rc, ie_coding->ti, "Error while encoding this IE"); } diff --git a/src/libosmo-gtlv/gtlv_gen.c b/src/libosmo-gtlv/gtlv_gen.c index fd3fbd9..9fe4b0c 100644 --- a/src/libosmo-gtlv/gtlv_gen.c +++ b/src/libosmo-gtlv/gtlv_gen.c @@ -388,7 +388,8 @@ "int %s_ies_encode(struct osmo_gtlv_put *gtlv, const union %s_ies *src,\n" " %s message_type, osmo_gtlv_err_cb err_cb, void *err_cb_data, const struct value_string *iei_strs)\n" "{\n" - " return osmo_gtlvs_encode(gtlv, src, 0, %s_get_msg_coding(message_type), err_cb, err_cb_data, iei_strs);\n" + " return osmo_gtlvs_encode(gtlv, src, sizeof(*src), 0, %s_get_msg_coding(message_type),\n" + " err_cb, err_cb_data, iei_strs);\n" "}\n", g_cfg->proto_name, g_cfg->proto_name, g_cfg->message_type_enum ? : "int", g_cfg->proto_name); printf("\n" diff --git a/tests/libosmo-gtlv/gtlv_dec_enc_test.c b/tests/libosmo-gtlv/gtlv_dec_enc_test.c index e02a2e5..63de266 100644 --- a/tests/libosmo-gtlv/gtlv_dec_enc_test.c +++ b/tests/libosmo-gtlv/gtlv_dec_enc_test.c @@ -387,7 +387,8 @@ .cfg = cfg, .dst = msgb_alloc(1024, __func__), }; - rc = osmo_gtlvs_encode(&put, (void *)orig, 0, msg_ie_coding, err_cb, &verify_err_cb_data, tag_names); + rc = osmo_gtlvs_encode(&put, (void *)orig, sizeof(*orig), 0, msg_ie_coding, + err_cb, &verify_err_cb_data, tag_names); printf("osmo_gtlvs_encode() rc = %d\n", rc); printf("%s.\n", osmo_hexdump(put.dst->data, put.dst->len)); -- To view, visit https://gerrit.osmocom.org/c/libosmo-pfcp/+/29039 To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: libosmo-pfcp Gerrit-Branch: master Gerrit-Change-Id: Id8d997c9d5e655ff1842ec69eab6c073875c6330 Gerrit-Change-Number: 29039 Gerrit-PatchSet: 1 Gerrit-Owner: neels &lt;nhofmeyr(a)sysmocom.de&gt; Gerrit-MessageType: newchange