Fuzz introspector
For issues and ideas: https://github.com/ossf/fuzz-introspector/issues
Project coverage
Per-fuzzer coverage

Table of contents

Project overview: libssh2
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: ssh2_client_fuzzer
Call tree
Fuzz blockers
Runtime coverage analysis
Files reached
Analyses and suggestions
Optimal target analysis
Remaining optimal interesting functions
All functions overview
Runtime coverage analysis
Complex functions with low coverage
Files and Directories in report
Files in report
Directories in report
Metadata section
Function call coverage
Function in each files in report
Report generation date: 2023-06-07

Project overview: libssh2

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
23.0%
78 / 341
Cyclomatic complexity statically reachable by fuzzers
28.0%
854 / 3038
Runtime code coverage of functions
36.0%
123 / 341

Warning: The number of runtime covered functions are larger than the number of reachable functions. This means that Fuzz Introspector found there are more functions covered at runtime than what is considered reachable based on the static analysis. This is a limitation in the analysis as anything covered at runtime is by definition reachable by the fuzzers.
This is likely due to a limitation in the static analysis. In this case, the count of functions covered at runtime is the true value, which means this is what should be considered "achieved" by the fuzzer.

Use the project functions table below to query all functions that were not covered at runtime.

Fuzzers overview

Fuzzer Fuzzer filename Functions Reached Functions unreached Fuzzer depth Files reached Basic blocks reached Cyclomatic complexity Details
ssh2_client_fuzzer /src/libssh2/tests/ossfuzz/ssh2_client_fuzzer.cc 106 395 13 13 2254 918 ssh2_client_fuzzer.cc

Project functions overview

The following table shows data about each function in the project. The functions included in this table correspond to all functions that exist in the executables of the fuzzers. As such, there may be functions that are from third-party libraries.

For further technical details on the meaning of columns in the below table, please see the Glossary .

Func name Functions filename Args Function call depth Reached by Fuzzers Fuzzers runtime hit Func lines hit % I Count BB Count Cyclomatic complexity Functions reached Reached by functions Accumulated cyclomatic complexity Undiscovered complexity

Fuzzer details

Fuzzer: ssh2_client_fuzzer

Call tree

The calltree shows the control flow of the fuzzer. This is overlaid with coverage information to display how much of the potential code a fuzzer can reach is in fact covered at runtime. In the following there is a link to a detailed calltree visualisation as well as a bitmap showing a high-level view of the calltree. For further information about these topics please see the glossary for full calltree and calltree overview

Full calltree

Call tree overview bitmap:

The distribution of callsites in terms of coloring is
Color Runtime hitcount Callsite count Percentage
red 0 203 40.1%
gold [1:9] 4 0.79%
yellow [10:29] 11 2.17%
greenyellow [30:49] 0 0.0%
lawngreen 50+ 287 56.8%
All colors 505 100

Fuzz blockers

The followings are the branches where fuzzer fails to bypass.

Unique non-covered Complexity Unique Reachable Complexities Unique Reachable Functions All non-covered Complexity All Reachable Complexity Function Name Function Callsite Blocked Branch
496 2144 14 :

['EVP_MD_CTX_free', '_libssh2_sha512_init', 'strlen', '_libssh2_packet_require', '_libssh2_htonu32', '_libssh2_sha256_init', 'BN_bn2bin', '_libssh2_debug_low', 'EVP_DigestFinal', 'EVP_DigestUpdate', '_libssh2_sha384_init', '_libssh2_transport_send', 'explicit_bzero', 'BN_num_bits']

498 2332 ecdh_sha2_nistp call site: 00000 /src/libssh2/src/kex.c:1878
318 1612 4 :

['_libssh2_transport_send', 'explicit_bzero', '_libssh2_sha_algo_value_hash', '_libssh2_packet_require']

326 1870 diffie_hellman_sha_algo call site: 00000 /src/libssh2/src/kex.c:632
96 1598 8 :

['EVP_MD_CTX_free', '_libssh2_sha256_init', '_libssh2_debug_low', 'EVP_DigestFinal', 'EVP_DigestUpdate', '_libssh2_transport_send', 'explicit_bzero', '_libssh2_packet_require']

98 1693 curve25519_sha256 call site: 00000 /src/libssh2/src/kex.c:2548
31 31 1 :

['_libssh2_dsa_sha1_verify']

31 31 hostkey_method_ssh_dss_sig_verify call site: 00000 /src/libssh2/src/hostkey.c:633
28 47 4 :

['_libssh2_channel_nextid', '_libssh2_list_add', '_libssh2_calloc', '_libssh2_debug_low']

28 1542 packet_x11_open call site: 00382 /src/libssh2/src/packet.c:349
25 44 3 :

['_libssh2_channel_nextid', '_libssh2_list_add', '_libssh2_debug_low']

25 1539 packet_authagent_open call site: 00407 /src/libssh2/src/packet.c:489
12 12 1 :

['_libssh2_sha384_init']

12 12 _libssh2_sha_algo_ctx_init call site: 00000 /src/libssh2/src/kex.c:114
11 11 2 :

['strchr', 'kex_get_method_by_name']

13 85 kex_agree_kex_hostkey call site: 00168 /src/libssh2/src/kex.c:3468
11 11 2 :

['strchr', 'kex_get_method_by_name']

13 33 kex_agree_hostkey call site: 00179 /src/libssh2/src/kex.c:3391
11 11 2 :

['strchr', 'kex_get_method_by_name']

13 33 kex_agree_crypt call site: 00190 /src/libssh2/src/kex.c:3547
11 11 2 :

['strchr', 'kex_get_method_by_name']

13 33 kex_agree_mac call site: 00200 /src/libssh2/src/kex.c:3611
11 11 2 :

['strchr', 'kex_get_method_by_name']

13 33 kex_agree_comp call site: 00211 /src/libssh2/src/kex.c:3664

Runtime coverage analysis

Covered functions
124
Functions that are reachable but not covered
39
Reachable functions
106
Percentage of reachable functions covered
63.21%
NB: The sum of covered functions and functions that are reachable but not covered need not be equal to Reachable functions . This is because the reachability analysis is an approximation and thus at runtime some functions may be covered that are not included in the reachability analysis. This is a limitation of our static analysis capabilities.
Warning: The number of covered functions are larger than the number of reachable functions. This means that there are more functions covered at runtime than are extracted using static analysis. This is likely a result of the static analysis component failing to extract the right call graph or the coverage runtime being compiled with sanitizers in code that the static analysis has not analysed. This can happen if lto/gold is not used in all places that coverage instrumentation is used.
Function name source code lines source lines hit percentage hit

Files reached

filename functions hit
/src/libssh2/tests/ossfuzz/ssh2_client_fuzzer.cc 1
global.c 3
../src/openssl.c 3
session.c 16
misc.c 17
kex.c 12
hostkey.c 1
crypt.c 1
mac.c 2
comp.c 1
transport.c 6
packet.c 6
channel.c 7

Analyses and suggestions

Optimal target analysis

Remaining optimal interesting functions

The following table shows a list of functions that are optimal targets. Optimal targets are identified by finding the functions that in combination, yield a high code coverage.

Func name Functions filename Arg count Args Function depth hitcount instr count bb count cyclomatic complexity Reachable functions Incoming references total cyclomatic complexity Unreached complexity
hostkey_method_ssh_ed25519_initPEMFromMemory /src/libssh2/src/hostkey.c 5 ['struct._LIBSSH2_SESSION *', 'char *', 'size_t ', 'char *', 'char **'] 5 0 89 14 6 124 0 594 517
kex_method_ecdh_key_exchange /src/libssh2/src/kex.c 2 ['struct._LIBSSH2_SESSION *', 'struct.key_exchange_state_low_t *'] 9 0 358 44 17 98 0 903 239
kex_method_curve25519_key_exchange /src/libssh2/src/kex.c 2 ['struct._LIBSSH2_SESSION *', 'struct.key_exchange_state_low_t *'] 9 0 359 45 17 96 0 830 162
kex_method_diffie_hellman_group_exchange_sha1_key_exchange /src/libssh2/src/kex.c 2 ['struct._LIBSSH2_SESSION *', 'struct.key_exchange_state_low_t *'] 8 0 329 35 14 97 0 843 160
_libssh2_pub_priv_keyfile /src/libssh2/src/../src/openssl.c 7 ['struct._LIBSSH2_SESSION *', 'char **', 'size_t *', 'char **', 'size_t *', 'char *', 'char *'] 3 0 164 16 4 121 0 513 57
libssh2_channel_read_ex /src/libssh2/src/channel.c 4 ['struct._LIBSSH2_CHANNEL *', 'int ', 'char *', 'size_t '] 8 0 169 33 10 69 0 698 53
libssh2_channel_direct_streamlocal_ex /src/libssh2/src/channel.c 4 ['struct._LIBSSH2_SESSION *', 'char *', 'char *', 'int '] 9 0 101 20 7 72 0 695 46
libssh2_poll /src/libssh2/src/session.c 3 ['struct._LIBSSH2_POLLFD *', 'int ', 'size_t '] 9 0 915 111 30 66 0 663 45
crypt_init_arcfour128 /src/libssh2/src/crypt.c 8 ['struct._LIBSSH2_SESSION *', 'struct._LIBSSH2_CRYPT_METHOD *', 'char *', 'int *', 'char *', 'int *', 'int ', 'char **'] 2 0 98 10 4 8 0 39 37
hostkey_method_ssh_ecdsa_sig_verify /src/libssh2/src/hostkey.c 6 ['struct._LIBSSH2_SESSION *', 'char *', 'size_t ', 'char *', 'size_t ', 'char **'] 2 0 140 20 9 23 0 70 35

Implementing fuzzers that target the above functions will improve reachability such that it becomes:

Functions statically reachable by fuzzers
51.0%
174 / 341
Cyclomatic complexity statically reachable by fuzzers
67.0%
2037 / 3038

All functions overview

If you implement fuzzers for these functions, the status of all functions in the project will be:

Func name Functions filename Args Function call depth Reached by Fuzzers Fuzzers runtime hit Func lines hit % I Count BB Count Cyclomatic complexity Functions reached Reached by functions Accumulated cyclomatic complexity Undiscovered complexity

Runtime coverage analysis

This section shows analysis of runtime coverage data.

For futher technical details on how this section is generated, please see the Glossary .

Complex functions with low coverage

Func name Function total lines Lines covered at runtime percentage covered Reached by fuzzers
libssh2_keepalive_send 31 7 22.58% ['ssh2_client_fuzzer']
kex_agree_kex_hostkey 48 22 45.83% ['ssh2_client_fuzzer']
kex_agree_hostkey 48 22 45.83% ['ssh2_client_fuzzer']
kex_agree_crypt 37 17 45.94% ['ssh2_client_fuzzer']
kex_agree_mac 41 22 53.65% ['ssh2_client_fuzzer']
kex_agree_comp 36 16 44.44% ['ssh2_client_fuzzer']
curve25519_sha256 393 168 42.74% []
ecdh_sha2_nistp 395 132 33.41% []
_libssh2_error_flags 31 15 48.38% ['ssh2_client_fuzzer']
_libssh2_debug_low 53 23 43.39% ['ssh2_client_fuzzer']
packet_queue_listener 170 70 41.17% ['ssh2_client_fuzzer']
packet_x11_open 146 61 41.78% ['ssh2_client_fuzzer']
packet_authagent_open 111 38 34.23% ['ssh2_client_fuzzer']
session_startup 106 39 36.79% ['ssh2_client_fuzzer']
session_free 206 94 45.63% ['ssh2_client_fuzzer']
_libssh2_transport_send 162 77 47.53% ['ssh2_client_fuzzer']
debugdump 47 10 21.27% ['ssh2_client_fuzzer']
fullpacket 103 34 33.00% ['ssh2_client_fuzzer']
send_existing 40 8 20.0% ['ssh2_client_fuzzer']

Files and Directories in report

This section shows which files and directories are considered in this report. The main reason for showing this is fuzz introspector may include more code in the reasoning than is desired. This section helps identify if too many files/directories are included, e.g. third party code, which may be irrelevant for the threat model. In the event too much is included, fuzz introspector supports a configuration file that can exclude data from the report. See the following link for more information on how to create a config file: link

Files in report

Source file Reached by Covered by
[] []
/src/libssh2/src/mac.c ['ssh2_client_fuzzer'] ['ssh2_client_fuzzer']
/src/libssh2/src/transport.c ['ssh2_client_fuzzer'] ['ssh2_client_fuzzer']
/src/libssh2/tests/ossfuzz/ssh2_client_fuzzer.cc ['ssh2_client_fuzzer'] ['ssh2_client_fuzzer']
/src/libssh2/src/packet.c ['ssh2_client_fuzzer'] ['ssh2_client_fuzzer']
/src/libssh2/src/../src/openssl.c ['ssh2_client_fuzzer'] []
/src/libssh2/src/pem.c [] []
/src/libssh2/src/crypt.c ['ssh2_client_fuzzer'] ['ssh2_client_fuzzer']
/src/libssh2/src/bcrypt_pbkdf.c [] []
/src/libssh2/src/global.c ['ssh2_client_fuzzer'] ['ssh2_client_fuzzer']
/src/libssh2/src/hostkey.c ['ssh2_client_fuzzer'] ['ssh2_client_fuzzer']
/src/libssh2/src/channel.c ['ssh2_client_fuzzer'] ['ssh2_client_fuzzer']
/src/libssh2/src/keepalive.c [] []
/src/libssh2/src/misc.c ['ssh2_client_fuzzer'] ['ssh2_client_fuzzer']
/src/libssh2/src/../src/blowfish.c [] []
/src/libssh2/src/comp.c ['ssh2_client_fuzzer'] ['ssh2_client_fuzzer']
/src/libssh2/src/session.c ['ssh2_client_fuzzer'] ['ssh2_client_fuzzer']
/src/libssh2/src/kex.c ['ssh2_client_fuzzer'] ['ssh2_client_fuzzer']

Directories in report

Directory
/src/libssh2/tests/ossfuzz/
/src/libssh2/src/../src/
/src/libssh2/src/

Metadata section

This sections shows the raw data that is used to produce this report. This is mainly used for further processing and developer debugging.

Fuzzer Calltree file Program data file Coverage file
ssh2_client_fuzzer fuzzerLogFile-0-wGdyOqaxw2.data fuzzerLogFile-0-wGdyOqaxw2.data.yaml ssh2_client_fuzzer.covreport