xref: /linux/tools/testing/selftests/bpf/bpf_arena_strsearch.h (revision 24f171c7e145f43b9f187578e89b0982ce87e54c)

/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) */
/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
#pragma once
#include "bpf_arena_common.h"

__noinline int bpf_arena_strlen(const char __arena *s __arg_arena)
{
	const char __arena *sc;

	for (sc = s; *sc != '\0'; ++sc)
		cond_break;
	return sc - s;
}

/**
 * glob_match - Shell-style pattern matching, like !fnmatch(pat, str, 0)
 * @pat: Shell-style pattern to match, e.g. "*.[ch]".
 * @str: String to match.  The pattern must match the entire string.
 *
 * Perform shell-style glob matching, returning true (1) if the match
 * succeeds, or false (0) if it fails.  Equivalent to !fnmatch(@pat, @str, 0).
 *
 * Pattern metacharacters are ?, *, [ and \.
 * (And, inside character classes, !, - and ].)
 *
 * This is small and simple implementation intended for device blacklists
 * where a string is matched against a number of patterns.  Thus, it
 * does not preprocess the patterns.  It is non-recursive, and run-time
 * is at most quadratic: strlen(@str)*strlen(@pat).
 *
 * An example of the worst case is glob_match("*aaaaa", "aaaaaaaaaa");
 * it takes 6 passes over the pattern before matching the string.
 *
 * Like !fnmatch(@pat, @str, 0) and unlike the shell, this does NOT
 * treat / or leading . specially; it isn't actually used for pathnames.
 *
 * Note that according to glob(7) (and unlike bash), character classes
 * are complemented by a leading !; this does not support the regex-style
 * [^a-z] syntax.
 *
 * An opening bracket without a matching close is matched literally.
 */
__noinline bool glob_match(char const __arena *pat __arg_arena, char const __arena *str __arg_arena)
{
	/*
	 * Backtrack to previous * on mismatch and retry starting one
	 * character later in the string.  Because * matches all characters
	 * (no exception for /), it can be easily proved that there's
	 * never a need to backtrack multiple levels.
	 */
	char const __arena *back_pat = NULL, *back_str;

	/*
	 * Loop over each token (character or class) in pat, matching
	 * it against the remaining unmatched tail of str.  Return false
	 * on mismatch, or true after matching the trailing nul bytes.
	 */
	for (;;) {
		unsigned char c = *str++;
		unsigned char d = *pat++;

		switch (d) {
		case '?':	/* Wildcard: anything but nul */
			if (c == '\0')
				return false;
			break;
		case '*':	/* Any-length wildcard */
			if (*pat == '\0')	/* Optimize trailing * case */
				return true;
			back_pat = pat;
			back_str = --str;	/* Allow zero-length match */
			break;
		case '[': {	/* Character class */
			bool match = false, inverted = (*pat == '!');
			char const __arena *class = pat + inverted;
			unsigned char a = *class++;

			/*
			 * Iterate over each span in the character class.
			 * A span is either a single character a, or a
			 * range a-b.  The first span may begin with ']'.
			 */
			do {
				unsigned char b = a;

				if (a == '\0')	/* Malformed */
					goto literal;

				if (class[0] == '-' && class[1] != ']') {
					b = class[1];

					if (b == '\0')
						goto literal;

					class += 2;
					/* Any special action if a > b? */
				}
				match |= (a <= c && c <= b);
				cond_break;
			} while ((a = *class++) != ']');

			if (match == inverted)
				goto backtrack;
			pat = class;
			}
			break;
		case '\\':
			d = *pat++;
			__attribute__((__fallthrough__));
		default:	/* Literal character */
literal:
			if (c == d) {
				if (d == '\0')
					return true;
				break;
			}
backtrack:
			if (c == '\0' || !back_pat)
				return false;	/* No point continuing */
			/* Try again from last *, one character later in str. */
			pat = back_pat;
			str = ++back_str;
			break;
		}
		cond_break;
	}
	return false;
}