1 files changed, 111 insertions, 0 deletions
diff --git a/libbb/xreadlink.c b/libbb/xreadlink.c
new file mode 100644
index 0000000..2cfc575
--- /dev/null
+++ b/libbb/xreadlink.c
@@ -0,0 +1,111 @@
+/* vi: set sw=4 ts=4: */
+/*
+ *  xreadlink.c - safe implementation of readlink.
+ *  Returns a NULL on failure...
+ */
+
+#include "libbb.h"
+
+/*
+ * NOTE: This function returns a malloced char* that you will have to free
+ * yourself.
+ */
+char* FAST_FUNC xmalloc_readlink(const char *path)
+{
+	enum { GROWBY = 80 }; /* how large we will grow strings by */
+
+	char *buf = NULL;
+	int bufsize = 0, readsize = 0;
+
+	do {
+		bufsize += GROWBY;
+		buf = xrealloc(buf, bufsize);
+		readsize = readlink(path, buf, bufsize);
+		if (readsize == -1) {
+			free(buf);
+			return NULL;
+		}
+	} while (bufsize < readsize + 1);
+
+	buf[readsize] = '\0';
+
+	return buf;
+}
+
+/*
+ * This routine is not the same as realpath(), which
+ * canonicalizes the given path completely. This routine only
+ * follows trailing symlinks until a real file is reached and
+ * returns its name. If the path ends in a dangling link or if
+ * the target doesn't exist, the path is returned in any case.
+ * Intermediate symlinks in the path are not expanded -- only
+ * those at the tail.
+ * A malloced char* is returned, which must be freed by the caller.
+ */
+char* FAST_FUNC xmalloc_follow_symlinks(const char *path)
+{
+	char *buf;
+	char *lpc;
+	char *linkpath;
+	int bufsize;
+	int looping = MAXSYMLINKS + 1;
+
+	buf = xstrdup(path);
+	goto jump_in;
+
+	while (1) {
+		linkpath = xmalloc_readlink(buf);
+		if (!linkpath) {
+			/* not a symlink, or doesn't exist */
+			if (errno == EINVAL || errno == ENOENT)
+				return buf;
+			goto free_buf_ret_null;
+		}
+
+		if (!--looping) {
+			free(linkpath);
+ free_buf_ret_null:
+			free(buf);
+			return NULL;
+		}
+
+		if (*linkpath != '/') {
+			bufsize += strlen(linkpath);
+			buf = xrealloc(buf, bufsize);
+			lpc = bb_get_last_path_component_strip(buf);
+			strcpy(lpc, linkpath);
+			free(linkpath);
+		} else {
+			free(buf);
+			buf = linkpath;
+ jump_in:
+			bufsize = strlen(buf) + 1;
+		}
+	}
+}
+
+char* FAST_FUNC xmalloc_readlink_or_warn(const char *path)
+{
+	char *buf = xmalloc_readlink(path);
+	if (!buf) {
+		/* EINVAL => "file: Invalid argument" => puzzled user */
+		bb_error_msg("%s: cannot read link (not a symlink?)", path);
+	}
+	return buf;
+}
+
+/* UNUSED */
+#if 0
+char* FAST_FUNC xmalloc_realpath(const char *path)
+{
+#if defined(__GLIBC__) && !defined(__UCLIBC__)
+	/* glibc provides a non-standard extension */
+	return realpath(path, NULL);
+#else
+	char buf[PATH_MAX+1];
+
+	/* on error returns NULL (xstrdup(NULL) ==NULL) */
+	return xstrdup(realpath(path, buf));
+#endif
+}
+#endif