From 0202865a1d8d5ffb8f312bf700d74fb4f43f14f5 Mon Sep 17 00:00:00 2001
From: Rob Landley <rob@landley.net>
Date: Sat, 27 Mar 2021 07:20:38 -0500
Subject: More cleanup of chsh.c

---
 toys/pending/chsh.c | 97 +++++++++++++++++------------------------------------
 1 file changed, 30 insertions(+), 67 deletions(-)

diff --git a/toys/pending/chsh.c b/toys/pending/chsh.c
index 194946de..c34660f7 100644
--- a/toys/pending/chsh.c
+++ b/toys/pending/chsh.c
@@ -28,93 +28,56 @@ GLOBALS(
 
 void chsh_main()
 {
-  int i;
   FILE *file;
-  size_t size, buf_size;
-  char *user, *line, *shell, *password, *encrypted;
+  char *user, *line, *shell, *encrypted;
   struct passwd *passwd_info;
   struct spwd *shadow_info;
-
-  // Use max login name size for buffer size
-  if (-1 == (buf_size = sysconf(_SC_LOGIN_NAME_MAX))) buf_size = 256;
-
-  if (!(user = malloc(buf_size * sizeof(user)))) perror_exit("Failed to allocate memory");
-  if (!(shell = malloc(buf_size * sizeof(shell)))) perror_exit("Failed to allocate memory");
-  if (!(line = malloc(buf_size * sizeof(line)))) perror_exit("Failed to allocate memory");
-  if (MAP_FAILED == (password = mmap(NULL, buf_size, PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS | MAP_LOCKED | MAP_NORESERVE, -1, 0))) perror_exit("Failed to get memory map");
+  int i;
 
   // Get uid user information, may be discarded later
-  if (!(passwd_info = getpwuid(getuid()))) perror_exit("Failed to get passwd record");
 
   if ((user = *toys.optargs)) {
-    errno = 0;
-    if (!(passwd_info = getpwnam(user)) && !errno) error_exit("Failed to get user info");
-
-    // Are we either root or changing our own shell?
-    if (getuid() && strcmp(passwd_info->pw_name, user)) error_exit("Permission denied\n");
-  } else user = passwd_info->pw_name;
+    passwd_info = xgetpwnam(user);
+    if (geteuid() && strcmp(passwd_info->pw_name, user))
+      error_exit("Permission denied\n");
+  } else {
+    passwd_info = xgetpwuid(getuid());
+    user = passwd_info->pw_name;
+  }
 
   // Get a password, encrypt it, wipe it, and check it
-  if (!(shadow_info = getspnam(passwd_info->pw_name))) perror_exit("Failed to get shadow record");
-  if (!read_password(password, buf_size, "Password: ")) error_exit("Failed to read password\n");
-  if (!(encrypted = crypt(password, shadow_info->sp_pwdp))) perror_exit("Failed to encrypt password");
-  memset(password, 0, buf_size);
-  if (!munmap(password, buf_size)) perror_exit("Failed to unmap memory");
-  if (strcmp(encrypted, shadow_info->sp_pwdp)) perror_exit("Incorrect password");
+  if (mlock(toybuf, sizeof(toybuf))) perror_exit("mlock");
+  if (!(shadow_info = getspnam(passwd_info->pw_name))) perror_exit("getspnam");
+  if (!read_password(toybuf, sizeof(toybuf), "Password: ")) xexit();
+  if (!(encrypted = crypt(toybuf, shadow_info->sp_pwdp))) perror_exit("crypt");
+  memset(toybuf, 0, sizeof(toybuf));
+  munlock(toybuf, sizeof(toybuf)); // prevents memset from "optimizing" away.
+  if (strcmp(encrypted, shadow_info->sp_pwdp)) perror_exit("Bad password");
 
   // Get new shell (either -s or interactive)
-  if (!(file = fopen("/etc/shells", "r"))) perror_exit("Failed to open /etc/shells");
+  file = xfopen("/etc/shells", "r");
   if (toys.optflags) shell = TT.s;
   else {
-    xprintf("Changing the login shell for %s\nEnter the new value, or press ENTER for default\n    Login shell [%s]: ", user, passwd_info->pw_shell);
-
-    errno = 0; size = 0;
-    while (EOF != (i = fgetc(stdin))) {
-      if (errno) perror_exit("Failed to read character from stdin");
-
-      if ('\n' != i) *(shell + size++) = i;
-      else {
-        *(shell + size) = '\0'; break;
-      }
-    }
+    xprintf("Changing the login shell for %s\n"
+            "Enter the new value, or press ENTER for default\n"
+            "    Login shell [%s]: ", user, passwd_info->pw_shell);
+    if (!(shell = xgetline(stdin))) xexit();
   }
 
-  // Is shell in /etc/shells?
-  if (strlen(shell)) {
-    line = NULL; size = 0; i = 0; errno = 0;
-
-    while (EOF != getline(&line, &size, file)) {
-      if (errno) perror_exit("Failed to read from /etc/shells");
-
-      size = strlen(line) - 1;
-      if ('\n' == *(line + size)) *(line + size) = '\0';
-
-      if (!strcmp(shell, line)) {
-        i = 1; break;
-      }
-    }
-
-    if (!i) error_exit("Shell not found in '/etc/shells'");
-  } else {
-
-    // Get default shell, ignoring comments and blank lines
-    do {
-      shell = NULL;
-      if (-1 == getline(&shell, &size, file)) perror_exit("Failed to read from /etc/shells");
-    } while (*shell != '/');
-
-    size = strlen(shell) - 1;
-    if ('\n' == *(shell + size)) *(shell + size) = '\0';
-  }
+  // Verify supplied shell in /etc/shells, or get default shell
+  if (strlen(shell))
+    while ((line = xgetline(file)) && strcmp(shell, line)) free(line);
+  else do line = xgetline(file); while (line && *line != '/');
+  if (!line) error_exit("Shell not found in '/etc/shells'");
 
   // Update shell and write passwd entry to tempfile
-  strncpy(passwd_info->pw_shell, shell, buf_size);
-  if (!(file = tmpfile())) perror_exit("Failed to create tempfile");
-  if (!putpwent(passwd_info, file)) perror_exit("Failed to write to passwd entry");
+  passwd_info->pw_shell = line;
+  if (!(file = tmpfile())) perror_exit("tmpfile");
+  if (!putpwent(passwd_info, file)) perror_exit("putpwent");
 
   // Move passwd entry from file to string
   if (-1 == (i = ftell(file))) perror_exit("Failed to get tempfile offset");
-  if (buf_size < i && !realloc(line, i)) perror_exit("Failed to reallocate memory");
+  if (sizeof(toybuf) < i && !realloc(line, i)) perror_exit("Failed to reallocate memory");
   rewind(file);
   if (fread(line, 1, i, file) < i) perror_exit("Failed to read from tempfile");
 
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