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prevent symlink loop recursion in directory traversal #289

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prevent symlink loop recursion in directory traversal #289

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46 changes: 35 additions & 11 deletions fuzzing/replay/file_util.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,9 @@

#include <cerrno>
#include <cstdio>
#include <set>
#include <string>
#include <utility>

#include "absl/functional/function_ref.h"
#include "absl/status/status.h"
Expand All @@ -36,7 +38,36 @@ namespace {

absl::Status TraverseDirectory(
absl::string_view path,
absl::FunctionRef<void(absl::string_view, const struct stat&)> callback) {
absl::FunctionRef<void(absl::string_view, const struct stat&)> callback,
std::set<std::pair<dev_t, ino_t>>& visited);

absl::Status YieldFilesInternal(
absl::string_view path,
absl::FunctionRef<void(absl::string_view, const struct stat&)> callback,
std::set<std::pair<dev_t, ino_t>>& visited) {
struct stat path_stat;
if (stat(std::string(path).c_str(), &path_stat) < 0) {
return ErrnoStatus(absl::StrCat("could not stat ", path), errno);
}
callback(path, path_stat);
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@simonresch simonresch May 13, 2026

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callback is here called unconditionally including on directories. This likely breaks existing behavior and fails the test for the file utility functions. You can run them on your end with the command bazel test //fuzzing/replay:file_util_test or bazel test //... to run all tests.

The direction to detect cycles on a pair of path_stat.st_dev, path_stat.st_ino makes sense to me.

if (S_ISDIR(path_stat.st_mode)) {
auto dir_id = std::make_pair(path_stat.st_dev, path_stat.st_ino);
if (!visited.count(dir_id)) {
// Prevent infinite recursion by tracking visited directories (dev,inode).
visited.insert(dir_id);
absl::Status status = TraverseDirectory(path, callback, visited);
if (!status.ok()) {
return status;
}
}
}
return absl::OkStatus();
}

absl::Status TraverseDirectory(
absl::string_view path,
absl::FunctionRef<void(absl::string_view, const struct stat&)> callback,
std::set<std::pair<dev_t, ino_t>>& visited) {
DIR* dir = opendir(std::string(path).c_str());
if (!dir) {
return ErrnoStatus(absl::StrCat("could not open directory ", path), errno);
Expand All @@ -58,7 +89,7 @@ absl::Status TraverseDirectory(
continue;
}
const std::string entry_path = absl::StrCat(path, "/", entry_name);
status.Update(YieldFiles(entry_path, callback));
status.Update(YieldFilesInternal(entry_path, callback, visited));
}
closedir(dir);
return status;
Expand All @@ -69,15 +100,8 @@ absl::Status TraverseDirectory(
absl::Status YieldFiles(
absl::string_view path,
absl::FunctionRef<void(absl::string_view, const struct stat&)> callback) {
struct stat path_stat;
if (stat(std::string(path).c_str(), &path_stat) < 0) {
return ErrnoStatus(absl::StrCat("could not stat ", path), errno);
}
if (S_ISDIR(path_stat.st_mode)) {
return TraverseDirectory(path, callback);
}
callback(path, path_stat);
return absl::OkStatus();
std::set<std::pair<dev_t, ino_t>> visited;
return YieldFilesInternal(path, callback, visited);
}

absl::Status SetFileContents(absl::string_view path,
Expand Down
28 changes: 28 additions & 0 deletions fuzzing/replay/file_util_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -16,8 +16,11 @@

#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include <cerrno>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <string>
#include <vector>
Expand Down Expand Up @@ -113,6 +116,31 @@ TEST(YieldFilesTest, YieldsHiddenFilesAndDirs) {
EXPECT_THAT(collected_paths, testing::SizeIs(2));
}

TEST(YieldFilesTest, DoesNotRecurseThroughSymlinkLoop) {
const std::string root_dir =
absl::StrCat(getenv("TEST_TMPDIR"), "/symlink-loop-root");
ASSERT_EQ(mkdir(root_dir.c_str(), 0755), 0);
const std::string dir_a = absl::StrCat(root_dir, "/dirA");
ASSERT_EQ(mkdir(dir_a.c_str(), 0755), 0);
const std::string dir_b = absl::StrCat(root_dir, "/dirB");
ASSERT_EQ(mkdir(dir_b.c_str(), 0755), 0);

const std::string link_to_b = absl::StrCat(dir_a, "/toB");
if (symlink(dir_b.c_str(), link_to_b.c_str()) != 0) {
GTEST_SKIP() << "symlink unsupported in this environment: "
<< std::strerror(errno);
}
const std::string link_to_a = absl::StrCat(dir_b, "/toA");
ASSERT_EQ(symlink(dir_a.c_str(), link_to_a.c_str()), 0);

std::vector<std::string> collected_paths;
const absl::Status status =
YieldFiles(root_dir, CollectPathsCallback(&collected_paths));
EXPECT_TRUE(status.ok());
EXPECT_GT(collected_paths.size(), 0);
EXPECT_LE(collected_paths.size(), 6);
Comment on lines +140 to +141
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@simonresch simonresch May 13, 2026

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The tests would need one or two normal files after adjusting the callback handling. Also, is there a reason to assert a range of size values instead of the exact number of expected files?

}

} // namespace

} // namespace fuzzing