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

Table of contents

Project overview: libpng
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: libpng_read_fuzzer
Call tree
Fuzz blockers
Runtime coverage analysis
Files reached
Analyses and suggestions
Optimal target analysis
Remaining optimal interesting functions
All functions overview
Fuzz engine guidance
/src/libpng/contrib/oss-fuzz/libpng_read_fuzzer.cc
Dictionary
Fuzzer function priority
Runtime coverage analysis
Complex functions with low coverage
Files and Directories in report
Files in report
Directories in report
Metadata section
Report generation date: 2025-07-11

Project overview: libpng

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
45.0%
181 / 401
Cyclomatic complexity statically reachable by fuzzers
56.9%
1835 / 3194
Runtime code coverage of functions
51.0%
204 / 401

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
libpng_read_fuzzer /src/libpng/contrib/oss-fuzz/libpng_read_fuzzer.cc 196 233 8 11 5403 2036 libpng_read_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 Runtime reached by Fuzzers Combined 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: libpng_read_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 0 388 56.5%
gold [1:9] 10 1.45%
yellow [10:29] 12 1.74%
greenyellow [30:49] 8 1.16%
lawngreen 50+ 268 39.0%
All colors 686 100

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
105 225 3 :

['OSS_FUZZ_png_destroy_read_struct', 'OSS_FUZZ_png_image_error', 'OSS_FUZZ_png_destroy_info_struct']

105 225 png_image_read_init call site: 00471 /src/libpng/pngread.c:1150
105 105 1 :

['OSS_FUZZ_png_image_error']

105 105 OSS_FUZZ_png_image_begin_read_from_memory call site: 00459 /src/libpng/pngread.c:1440
105 105 1 :

['OSS_FUZZ_png_image_error']

105 105 OSS_FUZZ_png_image_finish_read call site: 00494 /src/libpng/pngread.c:4037
104 203 7 :

['OSS_FUZZ_png_error', 'OSS_FUZZ_png_gamma_correct', 'OSS_FUZZ_png_warning', 'OSS_FUZZ_png_reciprocal2', 'OSS_FUZZ_png_reciprocal', 'OSS_FUZZ_png_gamma_significant', 'OSS_FUZZ_png_gamma_8bit_correct']

104 203 OSS_FUZZ_png_init_read_transformations call site: 00277 /src/libpng/pngrtran.c:1671
100 100 1 :

['png_cache_unknown_chunk']

185 257 OSS_FUZZ_png_handle_unknown call site: 00153 /src/libpng/pngrutil.c:2881
99 99 1 :

['OSS_FUZZ_png_set_rgb_coefficients']

203 438 OSS_FUZZ_png_init_read_transformations call site: 00237 /src/libpng/pngrtran.c:1512
91 91 1 :

['png_do_compose']

222 297 OSS_FUZZ_png_do_read_transformations call site: 00409 /src/libpng/pngrtran.c:4955
71 71 2 :

['OSS_FUZZ_png_set_strip_alpha', 'OSS_FUZZ_png_set_background_fixed']

78 1940 png_image_read_direct call site: 00632 /src/libpng/pngread.c:3695
50 50 2 :

['OSS_FUZZ_png_app_warning', 'OSS_FUZZ_png_app_error']

50 50 unsupported_gamma call site: 00585 /src/libpng/pngrtran.c:344
40 40 1 :

['OSS_FUZZ_png_set_rgb_to_gray_fixed']

152 2151 png_image_read_direct call site: 00623 /src/libpng/pngread.c:3570
34 34 1 :

['OSS_FUZZ_png_set_expand_16']

112 2008 png_image_read_direct call site: 00629 /src/libpng/pngread.c:3679
27 37 2 :

['png_do_rgb_to_gray', 'OSS_FUZZ_png_warning']

249 359 OSS_FUZZ_png_do_read_transformations call site: 00405 /src/libpng/pngrtran.c:4893

Runtime coverage analysis

Covered functions
212
Functions that are reachable but not covered
63
Reachable functions
196
Percentage of reachable functions covered
67.86%
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/libpng/contrib/oss-fuzz/libpng_read_fuzzer.cc 3
/src/libpng/png.c 33
/src/libpng/pngread.c 32
/src/libpng/pngmem.c 10
/src/libpng/pngerror.c 20
/src/libpng/pngrio.c 2
/src/libpng/pngrtran.c 38
/src/libpng/pngrutil.c 23
/src/libpng/pngset.c 5
/src/libpng/pngget.c 3
/src/libpng/pngtrans.c 13

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
png_handle_iCCP /src/libpng/pngrutil.c 3 ['N/A', 'N/A', 'int'] 9 0 547 79 28 41 0 261 93
png_handle_iTXt /src/libpng/pngrutil.c 3 ['N/A', 'N/A', 'int'] 8 0 479 80 28 36 0 237 86
OSS_FUZZ_png_set_sCAL /src/libpng/pngset.c 5 ['N/A', 'N/A', 'int', 'double', 'double'] 5 0 67 9 4 18 0 124 81
OSS_FUZZ_png_set_quantize /src/libpng/pngrtran.c 6 ['N/A', 'N/A', 'int', 'int', 'N/A', 'int'] 6 0 1626 190 58 14 0 113 58
OSS_FUZZ_png_read_png /src/libpng/pngread.c 4 ['N/A', 'N/A', 'int', 'N/A'] 11 0 384 67 22 132 0 1317 46
png_handle_pCAL /src/libpng/pngrutil.c 3 ['N/A', 'N/A', 'int'] 8 0 498 64 23 27 0 159 43
OSS_FUZZ_png_check_keyword /src/libpng/pngset.c 3 ['N/A', 'N/A', 'N/A'] 3 0 246 46 17 7 0 65 39
OSS_FUZZ_png_set_cHRM_XYZ /src/libpng/pngset.c 11 ['N/A', 'N/A', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double'] 6 0 74 3 2 14 0 70 39

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

Functions statically reachable by fuzzers
56.0%
225 / 401
Cyclomatic complexity statically reachable by fuzzers
72.0%
2312 / 3194

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 Runtime reached by Fuzzers Combined 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

Fuzz engine guidance

This sections provides heuristics that can be used as input to a fuzz engine when running a given fuzz target. The current focus is on providing input that is usable by libFuzzer.

/src/libpng/contrib/oss-fuzz/libpng_read_fuzzer.cc

Dictionary

Use this with the libFuzzer -dict=DICT.file flag


Fuzzer function priority

Use one of these functions as input to libfuzzer with flag: -focus_function name 

-focus_function=['LLVMFuzzerTestOneInput', 'OSS_FUZZ_png_gamma_16bit_correct', 'OSS_FUZZ_png_init_read_transformations', 'png_image_read_direct', 'png_image_skip_unused_chunks', 'OSS_FUZZ_png_set_alpha_mode_fixed', 'png_crc_finish_critical', 'OSS_FUZZ_png_chunk_report', 'OSS_FUZZ_png_do_read_transformations']

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
OSS_FUZZ_png_user_version_check 34 17 50.0% ['libpng_read_fuzzer']
OSS_FUZZ_png_zstream_error 36 17 47.22% ['libpng_read_fuzzer']
OSS_FUZZ_png_format_number 46 20 43.47% ['libpng_read_fuzzer']
png_image_read_direct 255 133 52.15% ['libpng_read_fuzzer']
OSS_FUZZ_png_set_crc_action 50 20 40.0% ['libpng_read_fuzzer']
OSS_FUZZ_png_set_alpha_mode_fixed 53 23 43.39% ['libpng_read_fuzzer']
OSS_FUZZ_png_init_read_transformations 365 97 26.57% ['libpng_read_fuzzer']
png_init_rgb_transformations 50 18 36.0% ['libpng_read_fuzzer']
png_do_gamma 169 88 52.07% ['libpng_read_fuzzer']
png_do_unpack 73 4 5.479% ['libpng_read_fuzzer']
png_do_read_filler 162 34 20.98% ['libpng_read_fuzzer']
OSS_FUZZ_png_handle_unknown 86 28 32.55% ['libpng_read_fuzzer']
OSS_FUZZ_png_combine_row 252 95 37.69% ['libpng_read_fuzzer']
OSS_FUZZ_png_do_read_interlace 199 34 17.08% ['libpng_read_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/libpng/pngerror.c ['libpng_read_fuzzer'] ['libpng_read_fuzzer']
/src/libpng/pngrtran.c ['libpng_read_fuzzer'] ['libpng_read_fuzzer']
/src/libpng/png.c ['libpng_read_fuzzer'] ['libpng_read_fuzzer']
/usr/local/bin/../include/c++/v1/stdexcept [] []
/src/libpng/pngrio.c ['libpng_read_fuzzer'] ['libpng_read_fuzzer']
/src/libpng/contrib/oss-fuzz/libpng_read_fuzzer.cc ['libpng_read_fuzzer'] ['libpng_read_fuzzer']
/src/libpng/pngmem.c ['libpng_read_fuzzer'] ['libpng_read_fuzzer']
/src/libpng/pngset.c ['libpng_read_fuzzer'] ['libpng_read_fuzzer']
/src/libpng/pngrutil.c ['libpng_read_fuzzer'] ['libpng_read_fuzzer']
/src/libpng/pngread.c ['libpng_read_fuzzer'] ['libpng_read_fuzzer']
/src/libpng/pngget.c ['libpng_read_fuzzer'] ['libpng_read_fuzzer']
/src/libpng/pngtrans.c ['libpng_read_fuzzer'] ['libpng_read_fuzzer']

Directories in report

Directory
/usr/local/bin/../include/c++/v1/
/src/libpng/
/src/libpng/contrib/oss-fuzz/

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
libpng_read_fuzzer fuzzerLogFile-0-fIAWhU8IeB.data fuzzerLogFile-0-fIAWhU8IeB.data.yaml libpng_read_fuzzer.covreport