Subject: [PATCH] fuzz: add fuzzer for config parsing

From: "Brian Tracy via GitGitGadget" <[email-masked]>
Date: Thu, 14 Mar 2024 06:41:18 +0000

From: Brian C Tracy <[email-masked]>

Add a new fuzz target that exercises the parsing of git configs.
The existing git_config_from_mem function is a perfect entry point
for fuzzing as it exercises the same code paths as the rest of the
config parsing functions and offers an easily fuzzable interface.

Config parsing is a useful thing to fuzz because it operates on user
controlled data and is a central component of many git operations.

Signed-off-by: Brian C Tracy <[email-masked]>
---
    fuzz: add fuzzer for config parsing

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1692%2Fbriantracy%2Fconfig-fuzzer-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1692/briantracy/config-fuzzer-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1692

 Makefile                            |  1 +
 ci/run-build-and-minimal-fuzzers.sh |  2 +-
 oss-fuzz/.gitignore                 |  1 +
 oss-fuzz/fuzz-config.c              | 32 +++++++++++++++++++++++++++++
 4 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 oss-fuzz/fuzz-config.c

diff --git a/Makefile b/Makefile
index 4e255c81f22..aa6c852548c 100644
--- a/Makefile
+++ b/Makefile
@@ -760,6 +760,7 @@ FUZZ_OBJS += oss-fuzz/fuzz-commit-graph.o
 FUZZ_OBJS += oss-fuzz/fuzz-date.o
 FUZZ_OBJS += oss-fuzz/fuzz-pack-headers.o
 FUZZ_OBJS += oss-fuzz/fuzz-pack-idx.o
+FUZZ_OBJS += oss-fuzz/fuzz-config.o
 .PHONY: fuzz-objs
 fuzz-objs: $(FUZZ_OBJS)
 
diff --git a/ci/run-build-and-minimal-fuzzers.sh b/ci/run-build-and-minimal-fuzzers.sh
index 8ba486f6598..29a21281f50 100755
--- a/ci/run-build-and-minimal-fuzzers.sh
+++ b/ci/run-build-and-minimal-fuzzers.sh
@@ -12,7 +12,7 @@ group "Build fuzzers" make \
 	LIB_FUZZING_ENGINE="-fsanitize=fuzzer,address" \
 	fuzz-all
 
-for fuzzer in commit-graph date pack-headers pack-idx ; do
+for fuzzer in commit-graph date pack-headers pack-idx config ; do
 	begin_group "fuzz-$fuzzer"
 	./oss-fuzz/fuzz-$fuzzer -verbosity=0 -runs=1 || exit 1
 	end_group "fuzz-$fuzzer"
diff --git a/oss-fuzz/.gitignore b/oss-fuzz/.gitignore
index 5b954088254..892fb09a95d 100644
--- a/oss-fuzz/.gitignore
+++ b/oss-fuzz/.gitignore
@@ -2,3 +2,4 @@ fuzz-commit-graph
 fuzz-date
 fuzz-pack-headers
 fuzz-pack-idx
+fuzz-config
diff --git a/oss-fuzz/fuzz-config.c b/oss-fuzz/fuzz-config.c
new file mode 100644
index 00000000000..5a1b39aa1e7
--- /dev/null
+++ b/oss-fuzz/fuzz-config.c
@@ -0,0 +1,32 @@
+#include "git-compat-util.h"
+#include "config.h"
+
+#include <stdio.h>
+#include <string.h>
+
+int LLVMFuzzerTestOneInput(const uint8_t *, size_t);
+static int config_parser_callback(const char *, const char *,
+					const struct config_context *, void *);
+
+static int config_parser_callback(const char *key, const char *value,
+					const struct config_context *ctx UNUSED,
+					void *data UNUSED)
+{
+	/* Visit every byte of memory we are given to make sure the parser
+	 * gave it to us appropriately. Ensure a return of 0 to indicate
+	 * success so the parsing continues. */
+	int c = strlen(key);
+	if (value)
+		c += strlen(value);
+	return c < 0;
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, const size_t size)
+{
+	struct config_options config_opts = { 0 };
+	config_opts.error_action = CONFIG_ERROR_SILENT;
+	git_config_from_mem(config_parser_callback, CONFIG_ORIGIN_BLOB,
+				"fuzztest-config", (const char *)data, size, NULL,
+				CONFIG_SCOPE_UNKNOWN, &config_opts);
+	return 0;
+}

base-commit: 945115026aa63df4ab849ab14a04da31623abece
-- 
gitgitgadget