Clean up su.

Stop building su as a static executable. We don't rely on the getuid
implementation for security, so we have nothing to fear from the dynamic
linker.

Add some missing error checking and improve error reporting.

Remove various special cases that can all be rolled into the general
case.

Bug: 19647373
Change-Id: I2689b8957a89da1f3be571fcdc966b1084efca9a

2 files changed, 58 insertions, 84 deletions

diff --git a/su/Android.mk b/su/Android.mk
index 0593cc96..297e0a31 100644
--- a/su/Android.mk
+++ b/su/Android.mk
@@ -1,14 +1,12 @@
 LOCAL_PATH:= $(call my-dir)
 include $(CLEAR_VARS)
 
+LOCAL_CFLAGS := -std=c11 -Wall -Werror
+
 LOCAL_SRC_FILES:= su.c
 
 LOCAL_MODULE:= su
 
-LOCAL_FORCE_STATIC_EXECUTABLE := true
-
-LOCAL_STATIC_LIBRARIES := libc
-
 LOCAL_MODULE_PATH := $(TARGET_OUT_OPTIONAL_EXECUTABLES)
 LOCAL_MODULE_TAGS := debug
 
diff --git a/su/su.c b/su/su.c
index 8365379f..75d68506 100644
--- a/su/su.c
+++ b/su/su.c
@@ -1,54 +1,45 @@
 /*
-**
-** Copyright 2008, The Android Open Source Project
-**
-** Licensed under the Apache License, Version 2.0 (the "License"); 
-** you may not use this file except in compliance with the License. 
-** You may obtain a copy of the License at 
-**
-**     http://www.apache.org/licenses/LICENSE-2.0 
-**
-** Unless required by applicable law or agreed to in writing, software 
-** distributed under the License is distributed on an "AS IS" BASIS, 
-** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
-** See the License for the specific language governing permissions and 
-** limitations under the License.
-*/
-
-#define LOG_TAG "su"
+ * Copyright (C) 2008 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
 
+#include <errno.h>
+#include <error.h>
+#include <pwd.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sys/types.h>
-#include <dirent.h>
-#include <errno.h>
-
 #include <unistd.h>
-#include <time.h>
-
-#include <pwd.h>
 
 #include <private/android_filesystem_config.h>
 
-
-void pwtoid(const char *tok, uid_t *uid, gid_t *gid)
-{
-    struct passwd *pw;
-    pw = getpwnam(tok);
+void pwtoid(const char* tok, uid_t* uid, gid_t* gid) {
+    struct passwd* pw = getpwnam(tok);
     if (pw) {
         if (uid) *uid = pw->pw_uid;
         if (gid) *gid = pw->pw_gid;
     } else {
-        uid_t tmpid = atoi(tok);
+        char* end;
+        errno = 0;
+        uid_t tmpid = strtoul(tok, &end, 10);
+        if (errno != 0 || end == tok) error(1, errno, "invalid uid/gid '%s'", tok);
         if (uid) *uid = tmpid;
         if (gid) *gid = tmpid;
     }
 }
 
-void extract_uidgids(const char *uidgids, uid_t *uid, gid_t *gid, gid_t *gids,
-                     int *gids_count)
-{
+void extract_uidgids(const char* uidgids, uid_t* uid, gid_t* gid, gid_t* gids, int* gids_count) {
     char *clobberablegids;
     char *nexttok;
     char *tok;
@@ -59,6 +50,7 @@ void extract_uidgids(const char *uidgids, uid_t *uid, gid_t *gid, gid_t *gids,
         *gids_count = 0;
         return;
     }
+
     clobberablegids = strdup(uidgids);
     strcpy(clobberablegids, uidgids);
     nexttok = clobberablegids;
@@ -87,7 +79,7 @@ void extract_uidgids(const char *uidgids, uid_t *uid, gid_t *gid, gid_t *gids,
 
 /*
  * SU can be given a specific command to exec. UID _must_ be
- * specified for this (ie argc => 3).
+ * specified for this.
  *
  * Usage:
  *   su 1000
@@ -99,61 +91,45 @@ void extract_uidgids(const char *uidgids, uid_t *uid, gid_t *gid, gid_t *gids,
  * will return
  *  uid=1000(system) gid=2000(shell) groups=3006(net_bw_stats),3007(net_bw_acct)
  */
-int main(int argc, char **argv)
-{
-    struct passwd *pw;
-    uid_t uid, myuid;
-    gid_t gid, gids[10];
+int main(int argc, char** argv) {
+    uid_t current_uid = getuid();
+    if (current_uid != AID_ROOT && current_uid != AID_SHELL) error(1, 0, "not allowed");
 
-    /* Until we have something better, only root and the shell can use su. */
-    myuid = getuid();
-    if (myuid != AID_ROOT && myuid != AID_SHELL) {
-        fprintf(stderr,"su: uid %d not allowed to su\n", myuid);
-        return 1;
-    }
+    // The default user is root.
+    uid_t uid = 0;
+    gid_t gid = 0;
 
-    if(argc < 2) {
-        uid = gid = 0;
-    } else {
+    // TODO: use getopt and support at least -- and --help.
+
+    // If there are any arguments, the first argument is the uid/gid/supplementary groups.
+    if (argc >= 2) {
+        gid_t gids[10];
         int gids_count = sizeof(gids)/sizeof(gids[0]);
         extract_uidgids(argv[1], &uid, &gid, gids, &gids_count);
-        if(gids_count) {
-            if(setgroups(gids_count, gids)) {
-                fprintf(stderr, "su: failed to set groups\n");
-                return 1;
+        if (gids_count) {
+            if (setgroups(gids_count, gids)) {
+                error(1, errno, "setgroups failed");
             }
         }
+        ++argv;
     }
 
-    if(setgid(gid) || setuid(uid)) {
-        fprintf(stderr,"su: permission denied\n");
-        return 1;
-    }
+    if (setgid(gid)) error(1, errno, "setgid failed");
+    if (setuid(uid)) error(1, errno, "setuid failed");
 
-    /* User specified command for exec. */
-    if (argc == 3 ) {
-        if (execlp(argv[2], argv[2], NULL) < 0) {
-            int saved_errno = errno;
-            fprintf(stderr, "su: exec failed for %s Error:%s\n", argv[2],
-                    strerror(errno));
-            return -saved_errno;
-        }
-    } else if (argc > 3) {
-        /* Copy the rest of the args from main. */
-        char *exec_args[argc - 1];
-        memset(exec_args, 0, sizeof(exec_args));
-        memcpy(exec_args, &argv[2], sizeof(exec_args));
-        if (execvp(argv[2], exec_args) < 0) {
-            int saved_errno = errno;
-            fprintf(stderr, "su: exec failed for %s Error:%s\n", argv[2],
-                    strerror(errno));
-            return -saved_errno;
-        }
-    }
+    // TODO: reset $PATH.
 
-    /* Default exec shell. */
-    execlp("/system/bin/sh", "sh", NULL);
+    // Set up the arguments for exec.
+    char* exec_args[argc];  // Having too much space is fine.
+    memset(exec_args, 0, sizeof(exec_args));
+    // Skip "su" and copy any other args. We already skipped the optional uid above.
+    ++argv;
+    for (size_t i = 0; argv[i] != NULL; ++i) {
+      exec_args[i] = argv[i];
+    }
+    // Default to the standard shell.
+    if (!exec_args[0]) exec_args[0] = "/system/bin/sh";
 
-    fprintf(stderr, "su: exec failed\n");
-    return 1;
+    execvp(exec_args[0], exec_args);
+    error(1, errno, "failed to exec %s", exec_args[0]);
 }