init: Check for symlinks with lstat() not open()

Using open() with an O_NOFOLLOW flag will result in a file falsely
being determined to be a symlink if the open fails for another
reason.

For example, a character device that isn't ready due to the
underlying hardware not being initialized yet will fail to open()

An example of this are any CG2900 device files prior to
execution of ste-cg29xx_ctrl

This uses lstat() instead of open() with O_NOFOLLOW to check
whether a file is a symlink or not.

Change-Id: Ie0d8d94b426c84c29b1b04d41a4cc15536cb307c

Author: Entropy512

init/builtins.c

@@ -77,61 +77,47 @@ static int write_file(const char *path, const char *value)
     }
 }
 
-static int _open(const char *path)
-{
-    int fd;
-
-    fd = open(path, O_RDONLY | O_NOFOLLOW);
-    if (fd < 0)
-        fd = open(path, O_WRONLY | O_NOFOLLOW);
-
-    return fd;
-}
 
 static int _chown(const char *path, unsigned int uid, unsigned int gid)
 {
-    int fd;
     int ret;
 
-    fd = _open(path);
-    if (fd < 0) {
+    struct stat p_statbuf;
+
+    ret = lstat(path, &p_statbuf);
+    if (ret < 0) {
         return -1;
     }
 
-    ret = fchown(fd, uid, gid);
-    if (ret < 0) {
-        int errno_copy = errno;
-        close(fd);
-        errno = errno_copy;
+    if (S_ISLNK(p_statbuf.st_mode) == 1) {
+        errno = EINVAL;
         return -1;
     }
 
-    close(fd);
+    ret = chown(path, uid, gid);
 
-    return 0;
+    return ret;
 }
 
 static int _chmod(const char *path, mode_t mode)
 {
-    int fd;
     int ret;
 
-    fd = _open(path);
-    if (fd < 0) {
+    struct stat p_statbuf;
+
+    ret = lstat(path, &p_statbuf);
+    if (ret < 0) {
         return -1;
     }
 
-    ret = fchmod(fd, mode);
-    if (ret < 0) {
-        int errno_copy = errno;
-        close(fd);
-        errno = errno_copy;
+    if (S_ISLNK(p_statbuf.st_mode) == 1) {
+        errno = EINVAL;
         return -1;
     }
 
-    close(fd);
+    ret = chmod(path, mode);
 
-    return 0;
+    return ret;
 }
 
 static int insmod(const char *filename, char *options)