/*

 * SPDX-License-Identifier: ISC

 *

 * Copyright (c) 2010-2015, 2020-2022 Todd C. Miller <Todd.Miller@sudo.ws>

 *

 * Permission to use, copy, modify, and distribute this software for any

 * purpose with or without fee is hereby granted, provided that the above

 * copyright notice and this permission notice appear in all copies.

 *

 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES

 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF

 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR

 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES

 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN

 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF

 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

 */

#include <config.h>

#include <sys/stat.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <unistd.h>

#include <errno.h>

#include <sudoers.h>

/*

 * Non-destructive word-split that handles single and double quotes and

 * escaped white space.  Quotes are only recognized at the start of a word.

 * They are treated as normal characters inside a word.

 */

static const char *

wordsplit(const char *str, const char *endstr, const char **last)

{

    const char *cp;

    debug_decl(wordsplit, SUDOERS_DEBUG_UTIL);

    /* If no str specified, use last ptr (if any). */

    if (str == NULL) {

  str = *last;

  /* Consume end quote if present. */

  if (*str == '"' || *str == '\'')

      str++;

    }

    /* Skip leading white space characters. */

    while (str < endstr && (*str == ' ' || *str == '\t'))

  str++;

    /* Empty string? */

    if (str >= endstr) {

  *last = endstr;

  debug_return_ptr(NULL);

    }

    /* If word is quoted, skip to end quote and return. */

    if (*str == '"' || *str == '\'') {

  const char *endquote;

  for (cp = str + 1; cp < endstr; cp = endquote + 1) {

      endquote = memchr(cp, *str, (size_t)(endstr - cp));

      if (endquote == NULL)

    break;

      /* ignore escaped quotes */

      if (endquote[-1] != '\\') {

    *last = endquote;

    debug_return_const_ptr(str + 1);

      }

  }

    }

    /* Scan str until we encounter white space. */

    for (cp = str; cp < endstr; cp++) {

  if (*cp == '\\' && cp + 1 < endstr) {

      /* quoted char, do not interpret */

      cp++;

      continue;

  }

  if (*cp == ' ' || *cp == '\t') {

      /* end of word */

      break;

  }

    }

    *last = cp;

    debug_return_const_ptr(str);

}

/* Copy len chars from string, collapsing chars escaped with a backslash. */

static char *

copy_arg(const char *src, size_t len)

{

    const char *src_end = src + len;

    char *copy, *dst;

    debug_decl(copy_arg, SUDOERS_DEBUG_UTIL);

    if ((copy = malloc(len + 1)) != NULL) {

  sudoers_gc_add(GC_PTR, copy);

  for (dst = copy; src < src_end; ) {

      if (*src == '\\' && src + 1 < src_end)

    src++;

      *dst++ = *src++;

  }

  *dst = '\0';

    }

    debug_return_ptr(copy);

}

/*

 * Search for the specified editor in the user's PATH, checking

 * the result against allowlist if non-NULL.  An argument vector

 * suitable for execve() is allocated and stored in argv_out.

 * If nfiles is non-zero, files[] is added to the end of argv_out.

 *

 * Returns the path to be executed on success, else NULL.

 * The caller is responsible for freeing the returned editor path

 * as well as the argument vector.

 */

static char *

resolve_editor(const char *ed, size_t edlen, int nfiles, char * const *files,

    int *argc_out, char ***argv_out, char * const *allowlist)

{

    char **nargv = NULL, *editor = NULL, *editor_path = NULL;

    const char *tmp, *cp, *ep = NULL;

    const char *edend = ed + edlen;

    struct stat user_editor_sb;

    int nargc = 0;

    debug_decl(resolve_editor, SUDOERS_DEBUG_UTIL);

    /*

     * Split editor into an argument vector, including files to edit.

     * The EDITOR and VISUAL environment variables may contain command

     * line args so look for those and alloc space for them too.

     */

    cp = wordsplit(ed, edend, &ep);

    if (cp == NULL)

  debug_return_str(NULL);

    editor = copy_arg(cp, (size_t)(ep - cp));

    if (editor == NULL)

  goto oom;

    /* If we can't find the editor in the user's PATH, give up. */

    if (find_path(editor, &editor_path, &user_editor_sb, getenv("PATH"), NULL,

      false, allowlist) != FOUND) {

  errno = ENOENT;

  goto bad;

    }

    /* Count rest of arguments and allocate editor argv. */

    for (nargc = 1, tmp = ep; wordsplit(NULL, edend, &tmp) != NULL; )

  nargc++;

    if (nfiles != 0)

  nargc += nfiles + 1;

    nargv = reallocarray(NULL, (size_t)nargc + 1, sizeof(char *));

    if (nargv == NULL)

  goto oom;

    sudoers_gc_add(GC_PTR, nargv);

    /* Fill in editor argv (assumes files[] is NULL-terminated). */

    nargv[0] = editor;

    editor = NULL;

    for (nargc = 1; (cp = wordsplit(NULL, edend, &ep)) != NULL; nargc++) {

  /* Copy string, collapsing chars escaped with a backslash. */

  nargv[nargc] = copy_arg(cp, (size_t)(ep - cp));

  if (nargv[nargc] == NULL)

      goto oom;

  /*

   * We use "--" to separate the editor and arguments from the files

   * to edit.  The editor arguments themselves may not contain "--".

   */

  if (strcmp(nargv[nargc], "--") == 0) {

      sudo_warnx(U_("ignoring editor: %.*s"), (int)edlen, ed);

      sudo_warnx("%s", U_("editor arguments may not contain \"--\""));

      errno = EINVAL;

      goto bad;

  }

    }

    if (nfiles != 0) {

  nargv[nargc++] = (char *)"--";

  do

      nargv[nargc++] = *files++;

  while (--nfiles > 0);

    }

    nargv[nargc] = NULL;

    *argc_out = nargc;

    *argv_out = nargv;

    debug_return_str(editor_path);

oom:

    sudo_warnx(U_("%s: %s"), __func__, U_("unable to allocate memory"));

bad:

    sudoers_gc_remove(GC_PTR, editor);

    free(editor);

    free(editor_path);

    if (nargv != NULL) {

  while (nargc > 0) {

      sudoers_gc_remove(GC_PTR, nargv[--nargc]);

      free(nargv[nargc]);

  }

  sudoers_gc_remove(GC_PTR, nargv);

  free(nargv);

    }

    debug_return_str(NULL);

}

/*

 * Determine which editor to use based on the SUDO_EDITOR, VISUAL and

 * EDITOR environment variables as well as the editor path in sudoers.

 *

 * Returns the path to be executed on success, else NULL.

 * The caller is responsible for freeing the returned editor path

 * as well as the argument vector.

 */

char *

find_editor(int nfiles, char * const *files, int *argc_out, char ***argv_out,

     char * const *allowlist, const char **env_editor)

{

    char *editor_path = NULL;

    const char *ev[3];

    size_t i;

    debug_decl(find_editor, SUDOERS_DEBUG_UTIL);

    /*

     * If any of SUDO_EDITOR, VISUAL or EDITOR are set, choose the first one.

     */

    *env_editor = NULL;

    ev[0] = "SUDO_EDITOR";

    ev[1] = "VISUAL";

    ev[2] = "EDITOR";

    for (i = 0; i < nitems(ev); i++) {

  char *editor = getenv(ev[i]);

  if (editor != NULL && *editor != '\0') {

      *env_editor = editor;

      editor_path = resolve_editor(editor, strlen(editor),

    nfiles, files, argc_out, argv_out, allowlist);

      if (editor_path != NULL)

    break;

      if (errno != ENOENT)

    debug_return_str(NULL);

  }

    }

    /*

     * If SUDO_EDITOR, VISUAL and EDITOR were either not set or not

     * allowed (based on the values of def_editor and def_env_editor),

     * choose the first one in def_editor that exists.

     */

    if (editor_path == NULL) {

  const char *def_editor_end = def_editor + strlen(def_editor);

  const char *cp, *ep;

  /* def_editor could be a path, split it up, avoiding strtok() */

  for (cp = sudo_strsplit(def_editor, def_editor_end, ":", &ep);

      cp != NULL; cp = sudo_strsplit(NULL, def_editor_end, ":", &ep)) {

      editor_path = resolve_editor(cp, (size_t)(ep - cp), nfiles,

    files, argc_out, argv_out, allowlist);

      if (editor_path != NULL)

    break;

      if (errno != ENOENT)

    debug_return_str(NULL);

  }

    }

    /* Caller is responsible for freeing editor_path, not g/c'd. */

    debug_return_str(editor_path);

}