/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Kenneth Almquist.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <paths.h>
#include <stdbool.h>
#include <stdlib.h>

/*
 * When commands are first encountered, they are entered in a hash table.
 * This ensures that a full path search will not have to be done for them
 * on each invocation.
 *
 * We should investigate converting to a linear search, even though that
 * would make the command name "hash" a misnomer.
 */

#include "shell.h"
#include "main.h"
#include "nodes.h"
#include "parser.h"
#include "redir.h"
#include "eval.h"
#include "exec.h"
#include "builtins.h"
#include "var.h"
#include "options.h"
#include "input.h"
#include "output.h"
#include "syntax.h"
#include "memalloc.h"
#include "error.h"
#include "mystring.h"
#include "show.h"
#include "jobs.h"
#include "alias.h"


#define CMDTABLESIZE 31         /* should be prime */



struct tblentry {
        struct tblentry *next;  /* next entry in hash chain */
        union param param;      /* definition of builtin function */
        int special;            /* flag for special builtin commands */
        signed char cmdtype;    /* index identifying command */
        char cmdname[];         /* name of command */
};


static struct tblentry *cmdtable[CMDTABLESIZE];
static int cmdtable_cd = 0;     /* cmdtable contains cd-dependent entries */


static void tryexec(char *, char **, char **);
static void printentry(struct tblentry *, int);
static struct tblentry *cmdlookup(const char *, int);
static void delete_cmd_entry(void);
static void addcmdentry(const char *, struct cmdentry *);



/*
 * Exec a program.  Never returns.  If you change this routine, you may
 * have to change the find_command routine as well.
 *
 * The argv array may be changed and element argv[-1] should be writable.
 */

void
shellexec(char **argv, char **envp, const char *path, int idx)
{
        char *cmdname;
        const char *opt;
        int e;

        if (strchr(argv[0], '/') != NULL) {
                tryexec(argv[0], argv, envp);
                e = errno;
        } else {
                e = ENOENT;
                while ((cmdname = padvance(&path, &opt, argv[0])) != NULL) {
                        if (--idx < 0 && opt == NULL) {
                                tryexec(cmdname, argv, envp);
                                if (errno != ENOENT && errno != ENOTDIR)
                                        e = errno;
                                if (e == ENOEXEC)
                                        break;
                        }
                        stunalloc(cmdname);
                }
        }

        /* Map to POSIX errors */
        if (e == ENOENT || e == ENOTDIR)
                errorwithstatus(127, "%s: not found", argv[0]);
        else
                errorwithstatus(126, "%s: %s", argv[0], strerror(e));
}


static bool
isbinary(const char *data, size_t len)
{
        const char *nul, *p;
        bool hasletter;

        nul = memchr(data, '\0', len);
        if (nul == NULL)
                return false;
        /*
         * POSIX says we shall allow execution if the initial part intended
         * to be parsed by the shell consists of characters and does not
         * contain the NUL character. This allows concatenating a shell
         * script (ending with exec or exit) and a binary payload.
         *
         * In order to reject common binary files such as PNG images, check
         * that there is a lowercase letter or expansion before the last
         * newline before the NUL character, in addition to the check for
         * the newline character suggested by POSIX.
         */
        hasletter = false;
        for (p = data; *p != '\0'; p++) {
                if ((*p >= 'a' && *p <= 'z') || *p == '$' || *p == '`')
                        hasletter = true;
                if (hasletter && *p == '\n')
                        return false;
        }
        return true;
}


static void
tryexec(char *cmd, char **argv, char **envp)
{
        int e, in;
        ssize_t n;
        char buf[256];

        execve(cmd, argv, envp);
        e = errno;
        if (e == ENOEXEC) {
                INTOFF;
                in = open(cmd, O_RDONLY | O_NONBLOCK);
                if (in != -1) {
                        n = pread(in, buf, sizeof buf, 0);
                        close(in);
                        if (n > 0 && isbinary(buf, n)) {
                                errno = ENOEXEC;
                                return;
                        }
                }
                *argv = cmd;
                *--argv = __DECONST(char *, _PATH_BSHELL);
                execve(_PATH_BSHELL, argv, envp);
        }
        errno = e;
}

/*
 * Do a path search.  The variable path (passed by reference) should be
 * set to the start of the path before the first call; padvance will update
 * this value as it proceeds.  Successive calls to padvance will return
 * the possible path expansions in sequence.  If popt is not NULL, options
 * are processed: if an option (indicated by a percent sign) appears in
 * the path entry then *popt will be set to point to it; else *popt will be
 * set to NULL.  If popt is NULL, percent signs are not special.
 */

char *
padvance(const char **path, const char **popt, const char *name)
{
        const char *p, *start;
        char *q;
        size_t len, namelen;

        if (*path == NULL)
                return NULL;
        start = *path;
        if (popt != NULL)
                for (p = start; *p && *p != ':' && *p != '%'; p++)
                        ; /* nothing */
        else
                for (p = start; *p && *p != ':'; p++)
                        ; /* nothing */
        namelen = strlen(name);
        len = p - start + namelen + 2;  /* "2" is for '/' and '\0' */
        STARTSTACKSTR(q);
        CHECKSTRSPACE(len, q);
        if (p != start) {
                memcpy(q, start, p - start);
                q += p - start;
                *q++ = '/';
        }
        memcpy(q, name, namelen + 1);
        if (popt != NULL) {
                if (*p == '%') {
                        *popt = ++p;
                        while (*p && *p != ':')  p++;
                } else
                        *popt = NULL;
        }
        if (*p == ':')
                *path = p + 1;
        else
                *path = NULL;
        return stalloc(len);
}



/*** Command hashing code ***/


int
hashcmd(int argc __unused, char **argv __unused)
{
        struct tblentry **pp;
        struct tblentry *cmdp;
        int c;
        int verbose;
        struct cmdentry entry;
        char *name;
        int errors;

        errors = 0;
        verbose = 0;
        while ((c = nextopt("rv")) != '\0') {
                if (c == 'r') {
                        clearcmdentry();
                } else if (c == 'v') {
                        verbose++;
                }
        }
        if (*argptr == NULL) {
                for (pp = cmdtable ; pp < &cmdtable[CMDTABLESIZE] ; pp++) {
                        for (cmdp = *pp ; cmdp ; cmdp = cmdp->next) {
                                if (cmdp->cmdtype == CMDNORMAL)
                                        printentry(cmdp, verbose);
                        }
                }
                return 0;
        }
        while ((name = *argptr) != NULL) {
                if ((cmdp = cmdlookup(name, 0)) != NULL
                 && cmdp->cmdtype == CMDNORMAL)
                        delete_cmd_entry();
                find_command(name, &entry, DO_ERR, pathval());
                if (entry.cmdtype == CMDUNKNOWN)
                        errors = 1;
                else if (verbose) {
                        cmdp = cmdlookup(name, 0);
                        if (cmdp != NULL)
                                printentry(cmdp, verbose);
                        else {
                                outfmt(out2, "%s: not found\n", name);
                                errors = 1;
                        }
                        flushall();
                }
                argptr++;
        }
        return errors;
}


static void
printentry(struct tblentry *cmdp, int verbose)
{
        int idx;
        const char *path, *opt;
        char *name;

        if (cmdp->cmdtype == CMDNORMAL) {
                idx = cmdp->param.index;
                path = pathval();
                do {
                        name = padvance(&path, &opt, cmdp->cmdname);
                        stunalloc(name);
                } while (--idx >= 0);
                out1str(name);
        } else if (cmdp->cmdtype == CMDBUILTIN) {
                out1fmt("builtin %s", cmdp->cmdname);
        } else if (cmdp->cmdtype == CMDFUNCTION) {
                out1fmt("function %s", cmdp->cmdname);
                if (verbose) {
                        INTOFF;
                        name = commandtext(getfuncnode(cmdp->param.func));
                        out1c(' ');
                        out1str(name);
                        ckfree(name);
                        INTON;
                }
#ifdef DEBUG
        } else {
                error("internal error: cmdtype %d", cmdp->cmdtype);
#endif
        }
        out1c('\n');
}



/*
 * Resolve a command name.  If you change this routine, you may have to
 * change the shellexec routine as well.
 */

void
find_command(const char *name, struct cmdentry *entry, int act,
    const char *path)
{
        struct tblentry *cmdp, loc_cmd;
        int idx;
        const char *opt;
        char *fullname;
        struct stat statb;
        int e;
        int i;
        int spec;
        int cd;

        /* If name contains a slash, don't use the hash table */
        if (strchr(name, '/') != NULL) {
                entry->cmdtype = CMDNORMAL;
                entry->u.index = 0;
                entry->special = 0;
                return;
        }

        cd = 0;

        /* If name is in the table, we're done */
        if ((cmdp = cmdlookup(name, 0)) != NULL) {
                if (cmdp->cmdtype == CMDFUNCTION && act & DO_NOFUNC)
                        cmdp = NULL;
                else
                        goto success;
        }

        /* Check for builtin next */
        if ((i = find_builtin(name, &spec)) >= 0) {
                INTOFF;
                cmdp = cmdlookup(name, 1);
                if (cmdp->cmdtype == CMDFUNCTION)
                        cmdp = &loc_cmd;
                cmdp->cmdtype = CMDBUILTIN;
                cmdp->param.index = i;
                cmdp->special = spec;
                INTON;
                goto success;
        }

        /* We have to search path. */

        e = ENOENT;
        idx = -1;
        for (;(fullname = padvance(&path, &opt, name)) != NULL;
            stunalloc(fullname)) {
                idx++;
                if (opt) {
                        if (strncmp(opt, "func", 4) == 0) {
                                /* handled below */
                        } else {
                                continue; /* ignore unimplemented options */
                        }
                }
                if (fullname[0] != '/')
                        cd = 1;
                if (stat(fullname, &statb) < 0) {
                        if (errno != ENOENT && errno != ENOTDIR)
                                e = errno;
                        continue;
                }
                e = EACCES;     /* if we fail, this will be the error */
                if (!S_ISREG(statb.st_mode))
                        continue;
                if (opt) {              /* this is a %func directory */
                        readcmdfile(fullname, -1 /* verify */);
                        if ((cmdp = cmdlookup(name, 0)) == NULL || cmdp->cmdtype != CMDFUNCTION)
                                error("%s not defined in %s", name, fullname);
                        stunalloc(fullname);
                        goto success;
                }
#ifdef notdef
                if (statb.st_uid == geteuid()) {
                        if ((statb.st_mode & 0100) == 0)
                                goto loop;
                } else if (statb.st_gid == getegid()) {
                        if ((statb.st_mode & 010) == 0)
                                goto loop;
                } else {
                        if ((statb.st_mode & 01) == 0)
                                goto loop;
                }
#endif
                TRACE(("searchexec \"%s\" returns \"%s\"\n", name, fullname));
                INTOFF;
                stunalloc(fullname);
                cmdp = cmdlookup(name, 1);
                if (cmdp->cmdtype == CMDFUNCTION)
                        cmdp = &loc_cmd;
                cmdp->cmdtype = CMDNORMAL;
                cmdp->param.index = idx;
                cmdp->special = 0;
                INTON;
                goto success;
        }

        if (act & DO_ERR) {
                if (e == ENOENT || e == ENOTDIR)
                        outfmt(out2, "%s: not found\n", name);
                else
                        outfmt(out2, "%s: %s\n", name, strerror(e));
        }
        entry->cmdtype = CMDUNKNOWN;
        entry->u.index = 0;
        entry->special = 0;
        return;

success:
        if (cd)
                cmdtable_cd = 1;
        entry->cmdtype = cmdp->cmdtype;
        entry->u = cmdp->param;
        entry->special = cmdp->special;
}



/*
 * Search the table of builtin commands.
 */

int
find_builtin(const char *name, int *special)
{
        const unsigned char *bp;
        size_t len;

        len = strlen(name);
        for (bp = builtincmd ; *bp ; bp += 2 + bp[0]) {
                if (bp[0] == len && memcmp(bp + 2, name, len) == 0) {
                        *special = (bp[1] & BUILTIN_SPECIAL) != 0;
                        return bp[1] & ~BUILTIN_SPECIAL;
                }
        }
        return -1;
}



/*
 * Called when a cd is done.  If any entry in cmdtable depends on the current
 * directory, simply clear cmdtable completely.
 */

void
hashcd(void)
{
        if (cmdtable_cd)
                clearcmdentry();
}



/*
 * Called before PATH is changed.  The argument is the new value of PATH;
 * pathval() still returns the old value at this point.  Called with
 * interrupts off.
 */

void
changepath(const char *newval __unused)
{
        clearcmdentry();
}


/*
 * Clear out cached utility locations.
 */

void
clearcmdentry(void)
{
        struct tblentry **tblp;
        struct tblentry **pp;
        struct tblentry *cmdp;

        INTOFF;
        for (tblp = cmdtable ; tblp < &cmdtable[CMDTABLESIZE] ; tblp++) {
                pp = tblp;
                while ((cmdp = *pp) != NULL) {
                        if (cmdp->cmdtype == CMDNORMAL) {
                                *pp = cmdp->next;
                                ckfree(cmdp);
                        } else {
                                pp = &cmdp->next;
                        }
                }
        }
        cmdtable_cd = 0;
        INTON;
}


static unsigned int
hashname(const char *p)
{
        unsigned int hashval;

        hashval = (unsigned char)*p << 4;
        while (*p)
                hashval += *p++;

        return (hashval % CMDTABLESIZE);
}


/*
 * Locate a command in the command hash table.  If "add" is nonzero,
 * add the command to the table if it is not already present.  The
 * variable "lastcmdentry" is set to point to the address of the link
 * pointing to the entry, so that delete_cmd_entry can delete the
 * entry.
 */

static struct tblentry **lastcmdentry;


static struct tblentry *
cmdlookup(const char *name, int add)
{
        struct tblentry *cmdp;
        struct tblentry **pp;
        size_t len;

        pp = &cmdtable[hashname(name)];
        for (cmdp = *pp ; cmdp ; cmdp = cmdp->next) {
                if (equal(cmdp->cmdname, name))
                        break;
                pp = &cmdp->next;
        }
        if (add && cmdp == NULL) {
                INTOFF;
                len = strlen(name);
                cmdp = *pp = ckmalloc(sizeof (struct tblentry) + len + 1);
                cmdp->next = NULL;
                cmdp->cmdtype = CMDUNKNOWN;
                memcpy(cmdp->cmdname, name, len + 1);
                INTON;
        }
        lastcmdentry = pp;
        return cmdp;
}

const void *
itercmd(const void *entry, struct cmdentry *result)
{
        const struct tblentry *e = entry;
        size_t i = 0;

        if (e != NULL) {
                if (e->next != NULL) {
                        e = e->next;
                        goto success;
                }
                i = hashname(e->cmdname) + 1;
        }
        for (; i < CMDTABLESIZE; i++)
                if ((e = cmdtable[i]) != NULL)
                        goto success;

        return (NULL);
success:
        result->cmdtype = e->cmdtype;
        result->cmdname = e->cmdname;

        return (e);
}

/*
 * Delete the command entry returned on the last lookup.
 */

static void
delete_cmd_entry(void)
{
        struct tblentry *cmdp;

        INTOFF;
        cmdp = *lastcmdentry;
        *lastcmdentry = cmdp->next;
        ckfree(cmdp);
        INTON;
}



/*
 * Add a new command entry, replacing any existing command entry for
 * the same name.
 */

static void
addcmdentry(const char *name, struct cmdentry *entry)
{
        struct tblentry *cmdp;

        INTOFF;
        cmdp = cmdlookup(name, 1);
        if (cmdp->cmdtype == CMDFUNCTION) {
                unreffunc(cmdp->param.func);
        }
        cmdp->cmdtype = entry->cmdtype;
        cmdp->param = entry->u;
        cmdp->special = entry->special;
        INTON;
}


/*
 * Define a shell function.
 */

void
defun(const char *name, union node *func)
{
        struct cmdentry entry;

        INTOFF;
        entry.cmdtype = CMDFUNCTION;
        entry.u.func = copyfunc(func);
        entry.special = 0;
        addcmdentry(name, &entry);
        INTON;
}


/*
 * Delete a function if it exists.
 * Called with interrupts off.
 */

int
unsetfunc(const char *name)
{
        struct tblentry *cmdp;

        if ((cmdp = cmdlookup(name, 0)) != NULL && cmdp->cmdtype == CMDFUNCTION) {
                unreffunc(cmdp->param.func);
                delete_cmd_entry();
                return (0);
        }
        return (0);
}


/*
 * Check if a function by a certain name exists.
 */
int
isfunc(const char *name)
{
        struct tblentry *cmdp;
        cmdp = cmdlookup(name, 0);
        return (cmdp != NULL && cmdp->cmdtype == CMDFUNCTION);
}


static void
print_absolute_path(const char *name)
{
        const char *pwd;

        if (*name != '/' && (pwd = lookupvar("PWD")) != NULL && *pwd != '\0') {
                out1str(pwd);
                if (strcmp(pwd, "/") != 0)
                        outcslow('/', out1);
        }
        out1str(name);
        outcslow('\n', out1);
}


/*
 * Shared code for the following builtin commands:
 *    type, command -v, command -V
 */

int
typecmd_impl(int argc, char **argv, int cmd, const char *path)
{
        struct cmdentry entry;
        struct tblentry *cmdp;
        const char *const *pp;
        struct alias *ap;
        int i;
        int error1 = 0;

        if (path != pathval())
                clearcmdentry();

        for (i = 1; i < argc; i++) {
                /* First look at the keywords */
                for (pp = parsekwd; *pp; pp++)
                        if (**pp == *argv[i] && equal(*pp, argv[i]))
                                break;

                if (*pp) {
                        if (cmd == TYPECMD_SMALLV)
                                out1fmt("%s\n", argv[i]);
                        else
                                out1fmt("%s is a shell keyword\n", argv[i]);
                        continue;
                }

                /* Then look at the aliases */
                if ((ap = lookupalias(argv[i], 1)) != NULL) {
                        if (cmd == TYPECMD_SMALLV) {
                                out1fmt("alias %s=", argv[i]);
                                out1qstr(ap->val);
                                outcslow('\n', out1);
                        } else
                                out1fmt("%s is an alias for %s\n", argv[i],
                                    ap->val);
                        continue;
                }

                /* Then check if it is a tracked alias */
                if ((cmdp = cmdlookup(argv[i], 0)) != NULL) {
                        entry.cmdtype = cmdp->cmdtype;
                        entry.u = cmdp->param;
                        entry.special = cmdp->special;
                }
                else {
                        /* Finally use brute force */
                        find_command(argv[i], &entry, 0, path);
                }

                switch (entry.cmdtype) {
                case CMDNORMAL: {
                        if (strchr(argv[i], '/') == NULL) {
                                const char *path2 = path;
                                const char *opt2;
                                char *name;
                                int j = entry.u.index;
                                do {
                                        name = padvance(&path2, &opt2, argv[i]);
                                        stunalloc(name);
                                } while (--j >= 0);
                                if (cmd != TYPECMD_SMALLV)
                                        out1fmt("%s is%s ", argv[i],
                                            (cmdp && cmd == TYPECMD_TYPE) ?
                                                " a tracked alias for" : "");
                                print_absolute_path(name);
                        } else {
                                if (eaccess(argv[i], X_OK) == 0) {
                                        if (cmd != TYPECMD_SMALLV)
                                                out1fmt("%s is ", argv[i]);
                                        print_absolute_path(argv[i]);
                                } else {
                                        if (cmd != TYPECMD_SMALLV)
                                                outfmt(out2, "%s: %s\n",
                                                    argv[i], strerror(errno));
                                        error1 |= 127;
                                }
                        }
                        break;
                }
                case CMDFUNCTION:
                        if (cmd == TYPECMD_SMALLV)
                                out1fmt("%s\n", argv[i]);
                        else
                                out1fmt("%s is a shell function\n", argv[i]);
                        break;

                case CMDBUILTIN:
                        if (cmd == TYPECMD_SMALLV)
                                out1fmt("%s\n", argv[i]);
                        else if (entry.special)
                                out1fmt("%s is a special shell builtin\n",
                                    argv[i]);
                        else
                                out1fmt("%s is a shell builtin\n", argv[i]);
                        break;

                default:
                        if (cmd != TYPECMD_SMALLV)
                                outfmt(out2, "%s: not found\n", argv[i]);
                        error1 |= 127;
                        break;
                }
        }

        if (path != pathval())
                clearcmdentry();

        return error1;
}

/*
 * Locate and print what a word is...
 */

int
typecmd(int argc, char **argv)
{
        if (argc > 2 && strcmp(argv[1], "--") == 0)
                argc--, argv++;
        return typecmd_impl(argc, argv, TYPECMD_TYPE, bltinlookup("PATH", 1));
}