fix: harden Linux procfs reads and ancestry traversal

[HiGarfield]

Motivation

• Avoid transient read failures when /proc or sysfs reads are interrupted by signals and prevent pathological infinite loops when traversing parent chains from inconsistent /proc snapshots.

Description

• Retry getline() on EINTR in read_line_from_file() to tolerate signal-interrupted reads and return the file contents only on real failures (file: src/util.c).
• Add a defensive next_ppid check in is_child_of() to reject invalid or self-parent links (next_ppid <= 0 || next_ppid == child_pid) and return non-descendant immediately to prevent endless loops (file: src/process_iterator_linux.c).
• Changes are minimal, localized, and preserve existing semantics while improving robustness under racey /proc conditions.

Testing

• Ran code formatting with cmake --build build --target format successfully.
• Built with GCC and Clang using cmake and cmake --build ... --target all with no build errors.
• Executed static analysis via the check target (cppcheck + clang-tidy) and found no report files with errors; the check target completed successfully.
• Ran the test suite and dynamic analysis with Valgrind (cmake --build build --target valgrind) and all unit/integration tests and valgrind runs passed with no leaks or errors.

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[Copilot]

Pull request overview

This PR improves robustness of Linux /proc/sysfs interactions by hardening single-line file reads against signal interruptions and making process ancestry traversal more defensive against inconsistent /proc snapshots.

Changes:

• Retry getline() on EINTR in read_line_from_file() to reduce transient /proc/sysfs read failures.
• Add a guard in Linux is_child_of() to avoid endless loops when a process reports an invalid/self parent link.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/util.c	Retries getline() on EINTR while reading first-line procfs/sysfs files.
src/process_iterator_linux.c	Adds defensive PPID validation during parent-chain traversal to prevent pathological loops.

[Copilot]

The EINTR retry loop should clear the stream error indicator before retrying. After a stdio call like getline() fails, the FILE error flag can remain set (sticky) and a subsequent getline() may immediately fail again unless clearerr(input_file) is called when errno==EINTR. Without clearing, this change may still return NULL on an interrupted read.

Suggested change

	* procfs/sysfs files.
	*/
	do {
	errno = 0;
	read_result = getline(&line, &line_size, input_file);
	* procfs/sysfs files. Because stdio stream error indicators are sticky,
	* clear the stream state before retrying after EINTR.
	*/
	do {
	errno = 0;
	read_result = getline(&line, &line_size, input_file);
	if (read_result < 0 && errno == EINTR) {
	clearerr(input_file);
	}

[HiGarfield]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Done in b1281ac. Added clearerr(input_file) inside the loop when errno == EINTR so the sticky stdio error indicator is cleared before each retry, matching the suggestion exactly.