X-Git-Url: https://git.librecmc.org/?a=blobdiff_plain;f=libbb%2Fxreadlink.c;h=7d4cb60a528f64b613a0aadf38afbd3a99b9bc4c;hb=a8cf9c5a3ffd1601872d1ab14c5be00fde29209c;hp=14863d9d5f75cae98fdcdcba8235614677eced43;hpb=63fc1a9e08fabfc8ba96bad80731673ef40bf5cb;p=oweals%2Fbusybox.git

diff --git a/libbb/xreadlink.c b/libbb/xreadlink.c
index 14863d9d5..7d4cb60a5 100644
--- a/libbb/xreadlink.c
+++ b/libbb/xreadlink.c
@@ -1,20 +1,24 @@
 /* vi: set sw=4 ts=4: */
 /*
- *  xreadlink.c - safe implementation of readlink.
- *  Returns a NULL on failure...
+ * xreadlink.c - safe implementation of readlink.
+ * Returns a NULL on failure.
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
  */
 
-#include <stdio.h>
+#include "libbb.h"
+
+/* Some systems (eg Hurd) do not have MAXSYMLINKS definition,
+ * set it to some reasonable value if it isn't defined */
+#ifndef MAXSYMLINKS
+# define MAXSYMLINKS 20
+#endif
 
 /*
  * NOTE: This function returns a malloced char* that you will have to free
- * yourself. You have been warned.
+ * yourself.
  */
-
-#include <unistd.h>
-#include "libbb.h"
-
-char *xreadlink(const char *path)
+char* FAST_FUNC xmalloc_readlink(const char *path)
 {
 	enum { GROWBY = 80 }; /* how large we will grow strings by */
 
@@ -22,17 +26,100 @@ char *xreadlink(const char *path)
 	int bufsize = 0, readsize = 0;
 
 	do {
-		buf = xrealloc(buf, bufsize += GROWBY);
-		readsize = readlink(path, buf, bufsize); /* 1st try */
+		bufsize += GROWBY;
+		buf = xrealloc(buf, bufsize);
+		readsize = readlink(path, buf, bufsize);
 		if (readsize == -1) {
-			bb_perror_msg("%s", path);
 			free(buf);
 			return NULL;
 		}
-	}
-	while (bufsize < readsize + 1);
+	} 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 */
+		const char *errmsg = "not a symlink";
+		int err = errno;
+		if (err != EINVAL)
+			errmsg = strerror(err);
+		bb_error_msg("%s: cannot read link: %s", path, errmsg);
+	}
+	return buf;
+}
+
+char* FAST_FUNC xmalloc_realpath(const char *path)
+{
+/* NB: uclibc also defines __GLIBC__
+ * Therefore the test "if glibc, or uclibc >= 0.9.31" looks a bit weird:
+ */
+#if defined(__GLIBC__) && \
+    (!defined(__UCLIBC__) || UCLIBC_VERSION >= KERNEL_VERSION(0, 9, 31))
+	/* glibc provides a non-standard extension */
+	/* new: POSIX.1-2008 specifies this behavior as well */
+	return realpath(path, NULL);
+#else
+	char buf[PATH_MAX+1];
+
+	/* on error returns NULL (xstrdup(NULL) == NULL) */
+	return xstrdup(realpath(path, buf));
+#endif
+}