From: Paul Eggert <eggert@cs.ucla.edu>
Date: Fri, 12 Jan 2007 21:54:50 +0000 (+0000)
Subject: * lib/xreadlink.c (SYMLINK_MAX) [!defined SYMLINK_MAX]: Define
X-Git-Tag: cvs-readonly~1359
X-Git-Url: http://erislabs.org.uk/gitweb/?a=commitdiff_plain;h=662e273931461d8aed89f64ea9ceb1618916e180;p=gnulib.git

* lib/xreadlink.c (SYMLINK_MAX) [!defined SYMLINK_MAX]: Define
to a reasonable default for memory allocation.
(xreadlink): Don't allocate a huge buffer, to work around a buggy
file system that reports garbage st_size values for symlinks.
Problem reported by Liyang Hu.
---

diff --git a/ChangeLog b/ChangeLog
index 6e7203b01..66fda758f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2007-01-12  Paul Eggert  <eggert@cs.ucla.edu>
+
+	* lib/xreadlink.c (SYMLINK_MAX) [!defined SYMLINK_MAX]: Define
+	to a reasonable default for memory allocation.
+	(xreadlink): Don't allocate a huge buffer, to work around a buggy
+	file system that reports garbage st_size values for symlinks.
+	Problem reported by Liyang Hu.
+
 2007-01-11  Simon Josefsson  <simon@josefsson.org>
 
 	* gnulib-tool (func_all_modules): Exclude all .* files (e.g.,
diff --git a/lib/xreadlink.c b/lib/xreadlink.c
index 8d61b633a..baea5b9cf 100644
--- a/lib/xreadlink.c
+++ b/lib/xreadlink.c
@@ -38,6 +38,13 @@
 # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
 #endif
 
+/* SYMLINK_MAX is used only for an initial memory-allocation sanity
+   check, so it's OK to guess too small on hosts where there is no
+   arbitrary limit to symbolic link length.  */
+#ifndef SYMLINK_MAX
+# define SYMLINK_MAX 1024
+#endif
+
 #define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX)
 
 #include "xalloc.h"
@@ -53,9 +60,17 @@
 char *
 xreadlink (char const *file, size_t size)
 {
-  /* The initial buffer size for the link value.  A power of 2
-     detects arithmetic overflow earlier, but is not required.  */
-  size_t buf_size = size < MAXSIZE ? size + 1 : MAXSIZE;
+  /* Some buggy file systems report garbage in st_size.  Defend
+     against them by ignoring outlandish st_size values in the initial
+     memory allocation.  */
+  size_t symlink_max = SYMLINK_MAX;
+  size_t INITIAL_LIMIT_BOUND = 8 * 1024;
+  size_t initial_limit = (symlink_max < INITIAL_LIMIT_BOUND
+			  ? symlink_max + 1
+			  : INITIAL_LIMIT_BOUND);
+
+  /* The initial buffer size for the link value.  */
+  size_t buf_size = size < initial_limit ? size + 1 : initial_limit;
 
   while (1)
     {