ftpd: add optional support for authentication

function                                             old     new   delta
cmdio_get_cmd_and_arg                                  -     237    +237
get_passwd                                             -      97     +97
check_password                                         -      82     +82
ftpd_main                                           2297    2178    -119
ask_and_check_password_extended                      206      84    -122
------------------------------------------------------------------------------
(add/remove: 3/0 grow/shrink: 0/2 up/down: 416/-241)          Total: 175 bytes

Signed-off-by: Morten Kvistgaard <MK@pch-engineering.dk>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

5 files changed, 100 insertions, 52 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 858084b..ff223dd 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1316,6 +1316,7 @@ int sd_listen_fds(void);
 #define SETUP_ENV_NO_CHDIR  (1 << 4)
 void setup_environment(const char *shell, int flags, const struct passwd *pw) FAST_FUNC;
 void nuke_str(char *str) FAST_FUNC;
+int check_password(const struct passwd *pw, const char *plaintext) FAST_FUNC;
 int ask_and_check_password_extended(const struct passwd *pw, int timeout, const char *prompt) FAST_FUNC;
 int ask_and_check_password(const struct passwd *pw) FAST_FUNC;
 /* Returns a malloced string */
diff --git a/libbb/Kbuild.src b/libbb/Kbuild.src
index 62680bd..0a9e803 100644
--- a/libbb/Kbuild.src
+++ b/libbb/Kbuild.src
@@ -150,6 +150,7 @@ lib-$(CONFIG_VLOCK) += pw_encrypt.o correct_password.o
 lib-$(CONFIG_SU) += pw_encrypt.o correct_password.o
 lib-$(CONFIG_LOGIN) += pw_encrypt.o correct_password.o
 lib-$(CONFIG_FEATURE_HTTPD_AUTH_MD5) += pw_encrypt.o
+lib-$(CONFIG_FEATURE_FTP_AUTHENTICATION) += pw_encrypt.o
 
 lib-$(CONFIG_DF) += find_mount_point.o
 lib-$(CONFIG_MKFS_MINIX) += find_mount_point.o
diff --git a/libbb/correct_password.c b/libbb/correct_password.c
index acadf39..513c930 100644
--- a/libbb/correct_password.c
+++ b/libbb/correct_password.c
@@ -30,6 +30,63 @@
 
 #include "libbb.h"
 
+#define SHADOW_BUFSIZE 256
+
+/* Retrieve encrypted password string for pw.
+ * If pw == NULL, return a string which fails password check against any
+ * password.
+ */
+#if !ENABLE_FEATURE_SHADOWPASSWDS
+#define get_passwd(pw, buffer) get_passwd(pw)
+#endif
+static const char *get_passwd(const struct passwd *pw, char buffer[SHADOW_BUFSIZE])
+{
+	const char *pass;
+
+	if (!pw)
+		return "aa"; /* "aa" will never match */
+
+	pass = pw->pw_passwd;
+#if ENABLE_FEATURE_SHADOWPASSWDS
+	/* Using _r function to avoid pulling in static buffers */
+	if ((pass[0] == 'x' || pass[0] == '*') && !pass[1]) {
+		struct spwd spw;
+		int r;
+		/* getspnam_r may return 0 yet set result to NULL.
+		 * At least glibc 2.4 does this. Be extra paranoid here. */
+		struct spwd *result = NULL;
+		r = getspnam_r(pw->pw_name, &spw, buffer, SHADOW_BUFSIZE, &result);
+		pass = (r || !result) ? "aa" : result->sp_pwdp;
+	}
+#endif
+	return pass;
+}
+
+/*
+ * Return 1 if PW has an empty password.
+ * Return 1 if the user gives the correct password for entry PW,
+ * 0 if not.
+ * NULL pw means "just fake it for login with bad username"
+ */
+int FAST_FUNC check_password(const struct passwd *pw, const char *plaintext)
+{
+	IF_FEATURE_SHADOWPASSWDS(char buffer[SHADOW_BUFSIZE];)
+	char *encrypted;
+	const char *pw_pass;
+	int r;
+
+	pw_pass = get_passwd(pw, buffer);
+	if (!pw_pass[0]) { /* empty password field? */
+		return 1;
+	}
+
+	encrypted = pw_encrypt(plaintext, /*salt:*/ pw_pass, 1);
+	r = (strcmp(encrypted, pw_pass) == 0);
+	free(encrypted);
+	return r;
+}
+
+
 /* Ask the user for a password.
  * Return 1 without asking if PW has an empty password.
  * Return -1 on EOF, error while reading input, or timeout.
@@ -41,42 +98,23 @@
 int FAST_FUNC ask_and_check_password_extended(const struct passwd *pw,
 		int timeout, const char *prompt)
 {
-	char *unencrypted, *encrypted;
-	const char *correct;
+	IF_FEATURE_SHADOWPASSWDS(char buffer[SHADOW_BUFSIZE];)
+	char *plaintext;
+	const char *pw_pass;
 	int r;
-	/* fake salt. crypt() can choke otherwise. */
-	correct = "aa";
-	if (!pw) {
-		/* "aa" will never match */
-		goto fake_it;
-	}
-	correct = pw->pw_passwd;
-#if ENABLE_FEATURE_SHADOWPASSWDS
-	/* Using _r function to avoid pulling in static buffers */
-	if ((correct[0] == 'x' || correct[0] == '*') && !correct[1]) {
-		struct spwd spw;
-		char buffer[256];
-		/* getspnam_r may return 0 yet set result to NULL.
-		 * At least glibc 2.4 does this. Be extra paranoid here. */
-		struct spwd *result = NULL;
-		r = getspnam_r(pw->pw_name, &spw, buffer, sizeof(buffer), &result);
-		correct = (r || !result) ? "aa" : result->sp_pwdp;
-	}
-#endif
 
-	if (!correct[0]) /* empty password field? */
+	pw_pass = get_passwd(pw, buffer);
+	if (!pw_pass[0]) /* empty password field? */
 		return 1;
 
- fake_it:
-	unencrypted = bb_ask(STDIN_FILENO, timeout, prompt);
-	if (!unencrypted) {
+	plaintext = bb_ask(STDIN_FILENO, timeout, prompt);
+	if (!plaintext) {
 		/* EOF (such as ^D) or error (such as ^C) or timeout */
 		return -1;
 	}
-	encrypted = pw_encrypt(unencrypted, correct, 1);
-	r = (strcmp(encrypted, correct) == 0);
-	free(encrypted);
-	nuke_str(unencrypted);
+
+	r = check_password(pw, plaintext);
+	nuke_str(plaintext);
 	return r;
 }
 
diff --git a/networking/Config.src b/networking/Config.src
index fbad7ec..e566469 100644
--- a/networking/Config.src
+++ b/networking/Config.src
@@ -134,6 +134,13 @@ config FEATURE_FTPD_ACCEPT_BROKEN_LIST
 	  it increases the code size by ~40 bytes.
 	  Most other ftp servers seem to behave similar to this.
 
+config FEATURE_FTP_AUTHENTICATION
+	bool "Enable authentication"
+	default y
+	depends on FTPD
+	help
+	  Enable basic system login as seen in telnet etc.
+
 config FTPGET
 	bool "ftpget"
 	default y
diff --git a/networking/ftpd.c b/networking/ftpd.c
index 2d2a3a4..9fcc3e9 100644
--- a/networking/ftpd.c
+++ b/networking/ftpd.c
@@ -1172,18 +1172,6 @@ int ftpd_main(int argc UNUSED_PARAM, char **argv)
 	if (logmode)
 		applet_name = xasprintf("%s[%u]", applet_name, (int)getpid());
 
-#if !BB_MMU
-	G.root_fd = -1;
-#endif
-	argv += optind;
-	if (argv[0]) {
-#if !BB_MMU
-		G.root_fd = xopen("/", O_RDONLY | O_DIRECTORY);
-		close_on_exec_on(G.root_fd);
-#endif
-		xchroot(argv[0]);
-	}
-
 	//umask(077); - admin can set umask before starting us
 
 	/* Signals. We'll always take -EPIPE rather than a rude signal, thanks */
@@ -1199,23 +1187,22 @@ int ftpd_main(int argc UNUSED_PARAM, char **argv)
 	WRITE_OK(FTP_GREET);
 	signal(SIGALRM, timeout_handler);
 
-#ifdef IF_WE_WANT_TO_REQUIRE_LOGIN
+#if ENABLE_FEATURE_FTP_AUTHENTICATION
 	{
-		smallint user_was_specified = 0;
+		struct passwd *pw = NULL;
+
 		while (1) {
 			uint32_t cmdval = cmdio_get_cmd_and_arg();
 
 			if (cmdval == const_USER) {
-				if (G.ftp_arg == NULL || strcasecmp(G.ftp_arg, "anonymous") != 0)
-					cmdio_write_raw(STR(FTP_LOGINERR)" Server is anonymous only\r\n");
-				else {
-					user_was_specified = 1;
-					cmdio_write_raw(STR(FTP_GIVEPWORD)" Please specify the password\r\n");
-				}
+				pw = getpwnam(G.ftp_arg);
+				cmdio_write_raw(STR(FTP_GIVEPWORD)" Please specify password\r\n");
 			} else if (cmdval == const_PASS) {
-				if (user_was_specified)
-					break;
-				cmdio_write_raw(STR(FTP_NEEDUSER)" Login with USER\r\n");
+				if (check_password(pw, G.ftp_arg) > 0) {
+					break;	/* login success */
+				}
+				cmdio_write_raw(STR(FTP_LOGINERR)" Login failed\r\n");
+				pw = NULL;
 			} else if (cmdval == const_QUIT) {
 				WRITE_OK(FTP_GOODBYE);
 				return 0;
@@ -1223,10 +1210,24 @@ int ftpd_main(int argc UNUSED_PARAM, char **argv)
 				cmdio_write_raw(STR(FTP_LOGINERR)" Login with USER and PASS\r\n");
 			}
 		}
+		change_identity(pw);
 	}
 	WRITE_OK(FTP_LOGINOK);
 #endif
 
+	/* Do this after auth, else /etc/passwd is not accessible */
+#if !BB_MMU
+	G.root_fd = -1;
+#endif
+	argv += optind;
+	if (argv[0]) {
+#if !BB_MMU
+		G.root_fd = xopen("/", O_RDONLY | O_DIRECTORY);
+		close_on_exec_on(G.root_fd);
+#endif
+		xchroot(argv[0]);
+	}
+
 	/* RFC-959 Section 5.1
 	 * The following commands and options MUST be supported by every
 	 * server-FTP and user-FTP, except in cases where the underlying