/*

 * Shared helpers for R fuzzing harnesses (libFuzzer).

 *

 * Provides:

 *   fuzz_suppress_warnings() - Suppress R warnings to avoid buffer overflow

 *   fuzz_init_r()            - Full R initialization sequence

 *   fuzz_set_string()        - Stage a string input under a toplevel context

 *   fuzz_set_raw_arg()       - Stage a raw-vector input likewise

 *   fuzz_repeat_product_excessive() - Guard against TRE repeat blowup

 *

 * Adapted from r-afl's fuzz.h for use with libFuzzer instead of AFL++.

 */

#ifndef FUZZ_COMMON_H

#define FUZZ_COMMON_H

#include <limits.h>

#include <stdint.h>

#include <stdlib.h>

#include <string.h>

#include <unistd.h>

#define R_NO_REMAP 1

#include <Rembedded.h>

#include <Rinternals.h>

#include <Rinterface.h>   /* R_SignalHandlers */

#include <R_ext/Parse.h>

/*

 * Suppress R warnings globally.

 *

 * Many R functions emit warnings on invalid input (e.g., "NAs introduced

 * by coercion").  In persistent fuzzing, these accumulate and can overflow

 * R's warning buffer, triggering fatal errors.  Setting warn = -1

 * suppresses all warnings.

 */

static void fuzz_suppress_warnings(void)

{

    int error = 0;

    SEXP warn_call;

    Rf_protect(warn_call = Rf_lang2(Rf_install("options"),

                                    Rf_ScalarInteger(-1)));

    SET_TAG(CDR(warn_call), Rf_install("warn"));

    R_tryEval(warn_call, R_GlobalEnv, &error);

    Rf_unprotect(1);

}

/*

 * Set R_HOME based on the fuzzer binary's location.

 *

 * OSS-Fuzz places everything in $OUT.  The build.sh installs R to

 * $OUT/r-install, so R_HOME is at $OUT/r-install/lib/R.  We derive

 * this from /proc/self/exe so it works regardless of the mount path.

 */

static void fuzz_set_r_home(void)

{

    /* Skip if R_HOME is already set (e.g., for local testing) */

    if (getenv("R_HOME") != NULL)

        return;

    char exe[PATH_MAX];

    ssize_t len = readlink("/proc/self/exe", exe, sizeof(exe) - 1);

    if (len <= 0)

        return;

    exe[len] = '\0';

    /* Find the directory containing the binary */

    char *slash = strrchr(exe, '/');

    if (slash == NULL)

        return;

    *slash = '\0';

    char r_home[PATH_MAX];

    snprintf(r_home, sizeof(r_home), "%s/r-install/lib/R", exe);

    setenv("R_HOME", r_home, 1);

}

/*

 * Cap R's vector heap.

 *

 * Hostile input reaches R's allocator directly -- a serialized vector can

 * declare any length it likes, and coercion or scanning can be talked into

 * asking for one -- so a 64KB input can request gigabytes.

 *

 * R enforces R_MAX_VSIZE in allocVector and signals an ordinary R error

 * ("vector memory limit of N reached").  When it fires inside R_ToplevelExec

 * the iteration is discarded and fuzzing carries on; every per-iteration

 * allocation must therefore go through fuzz_set_string / fuzz_set_raw_arg

 * below, which run under such a context.  That catchability is the reason

 * to prefer this over a sanitizer-level RSS limit: ASAN's soft_rss_limit_mb

 * either aborts the process or starts handing NULL back to allocators that

 * never expected it, and both look like crashes.

 *

 * Caveats:

 *   - The cap bounds R's cumulative LIVE vector heap, not one input's

 *     allocations.  Interned symbols are never collected, so the parse and

 *     unserialize targets ratchet toward the cap over a long run.

 *   - It bounds R's vector heap ONLY.  malloc-based allocations, like TRE

 *     compiling a pattern, bypass it entirely; see

 *     fuzz_repeat_product_excessive for that guard.

 *   - It does cost coverage of code paths that need larger results.

 *     Targets with legitimately large outputs (decompress: a 64KB bzip2

 *     stream of zeros expands past 1GB) raise the default by defining

 *     FUZZ_R_MAX_VSIZE before including this header.

 *   - R's suffix parsing is case-sensitive: "4Gb" works, "4gb" silently

 *     leaves the heap uncapped (R only warns on stderr at startup).  The

 *     env override is for local runs; the CI runner does not forward

 *     arbitrary environment variables.

 *

 * Local reproduction of vector-limit findings under plain Rscript needs

 * the same value exported; see README.md.

 */

#ifndef FUZZ_R_MAX_VSIZE

# define FUZZ_R_MAX_VSIZE "1Gb"

#endif

static void fuzz_set_vsize_limit(void)

{

    if (getenv("R_MAX_VSIZE") == NULL)

        setenv("R_MAX_VSIZE", FUZZ_R_MAX_VSIZE, 1);

}

/*

 * Initialize R for fuzzing.  Call once from LLVMFuzzerInitialize.

 *

 * Performs:

 *   1. Set R_HOME from binary location

 *   2. Cap the vector heap (must precede R's startup, which reads it)

 *   3. Initialize embedded R, without R's signal handlers

 *   4. Suppress warnings

 */

static void fuzz_init_r(void)

{

    fuzz_set_r_home();

    fuzz_set_vsize_limit();

    /* R's SIGSEGV/SIGILL/etc. handlers enter an interactive recovery

     * prompt instead of crashing, which would hang the fuzzer.  Telling

     * R not to install them (rather than resetting to SIG_DFL after

     * init) keeps the sanitizers' own handlers in place, so wild-pointer

     * faults still get full ASAN reports and clean deduplication. */

    R_SignalHandlers = 0;

    char *r_argv[] = {"R", "--vanilla", "--no-echo", "--no-restore"};

    int r_argc = sizeof(r_argv) / sizeof(r_argv[0]);

    Rf_initEmbeddedR(r_argc, r_argv);

    fuzz_suppress_warnings();

}

/*

 * Helper for protected evaluation via R_ToplevelExec.

 *

 * R API calls that touch R objects can longjmp on error.  Without a

 * top-level context, R's error handler crashes.  Wrapping calls in

 * R_ToplevelExec catches the longjmp cleanly.

 */

typedef struct {

    SEXP call;

    SEXP env;

} fuzz_eval_data_t;

static void fuzz_do_eval(void *data)

{

    fuzz_eval_data_t *ed = (fuzz_eval_data_t *)data;

    Rf_eval(ed->call, ed->env);

}

/*

 * Stage per-iteration inputs under a toplevel context.

 *

 * Rf_mkChar and Rf_allocVector can themselves signal the vector-limit

 * error.  Outside a toplevel context that error longjmps into a stack

 * frame that returned during Rf_initEmbeddedR -- undefined behaviour --

 * so input staging must be wrapped just like evaluation.  Both helpers

 * return FALSE when the allocation failed; skip the iteration then.

 */

typedef struct {

    SEXP vec;

    const char *str;

} fuzz_string_data_t;

static void fuzz_do_set_string(void *data)

{

    fuzz_string_data_t *sd = (fuzz_string_data_t *)data;

    SET_STRING_ELT(sd->vec, 0, Rf_mkChar(sd->str));

}

static Rboolean fuzz_set_string(SEXP vec, const char *str)

{

    fuzz_string_data_t sd = { vec, str };

    return R_ToplevelExec(fuzz_do_set_string, &sd);

}

typedef struct {

    SEXP call;

    const uint8_t *data;

    size_t size;

} fuzz_raw_data_t;

static void fuzz_do_set_raw(void *data)

{

    fuzz_raw_data_t *rd = (fuzz_raw_data_t *)data;

    /* The raw vector is reachable from the (protected) call as soon as

     * SETCADR runs, and nothing allocates before the memcpy completes,

     * so no extra protection is needed. */

    SEXP raw = Rf_allocVector(RAWSXP, (R_xlen_t)rd->size);

    SETCADR(rd->call, raw);

    memcpy(RAW(raw), rd->data, rd->size);

}

static Rboolean fuzz_set_raw_arg(SEXP call, const uint8_t *data, size_t size)

{

    fuzz_raw_data_t rd = { call, data, size };

    return R_ToplevelExec(fuzz_do_set_raw, &rd);

}

/*

 * Guard against TRE's bounded-repeat blowup.

 *

 * TRE compiles bounded repeats by duplicating the pattern AST, so nested

 * counted repeats multiply: a 36-byte pattern like

 * (?:a{2,101,})(?:a{2,101,}){100}{100} expands to ~10^8 nodes and >8GB of

 * allocations at compile time.  Those allocations are malloc, not R's

 * vector heap, so R_MAX_VSIZE cannot bound them; reject the pattern

 * before it reaches R instead.

 *

 * The product of all repeat bounds is a deliberate over-estimate --

 * sequential (non-nested) repeats add rather than multiply -- trading a

 * little coverage of repeat-heavy patterns for a hard bound on compile

 * cost.

 */

#define FUZZ_MAX_REPEAT_PRODUCT 1000000.0

static int fuzz_repeat_product_excessive(const char *pattern)

{

    double product = 1.0;

    for (const char *p = pattern; *p != '\0'; p++) {

        if (*p != '{')

            continue;

        /* The largest number inside the braces bounds this repeat. */

        unsigned long bound = 0, cur = 0;

        int counted = 0;

        const char *q = p + 1;

        for (; *q != '\0' && *q != '}'; q++) {

            if (*q >= '0' && *q <= '9') {

                cur = cur * 10 + (unsigned long)(*q - '0');

                if (cur > 10000000)

                    cur = 10000000;  /* saturate; already over any budget */

                counted = 1;

            } else if (*q == ',') {

                if (cur > bound)

                    bound = cur;

                cur = 0;

            } else {

                counted = 0;  /* not a counted repeat, e.g. "{a}" */

                break;

            }

        }

        if (!counted || *q != '}')

            continue;

        if (cur > bound)

            bound = cur;

        if (bound > 1)

            product *= (double)bound;

        if (product > FUZZ_MAX_REPEAT_PRODUCT)

            return 1;

        p = q;

    }

    return 0;

}

#endif /* FUZZ_COMMON_H */