[Libcdio-devel] [PATCH] Non LFS dependent fseeko detection and off_t truncation checks

[Pete Batard]

Last commit of mine from -pbatard (= attached patch) fixes the issue 
previous observed on ARM and cygwin by:

- adding fseeko detection that doesn't rely on LFS
- detecting truncation of off_t when LFS is in use but fseeko was not 
detected.

Regards,

/Pete

PS: We got a merge in git as 2 of us were pushing into the repo around 
the same time
>From ecfdf70a08ae99b04050b00b752cc25728f1d537 Mon Sep 17 00:00:00 2001
From: Pete Batard <address@hidden>
Date: Wed, 25 Jan 2012 01:03:53 +0000
Subject: [PATCH] Non LFS dependent fseeko detection and off_t truncation
 checks

* On some systems, LFS may be enabled (64 bit off_t) but fseeko
  is not properly detected
* When this occurs, seek will truncate off_t to long resulting
  in data corruption
---
 configure.ac             |   15 +++++++++++++--
 lib/driver/_cdio_stdio.c |    8 ++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/configure.ac b/configure.ac
index 4f124f2..0b76d39 100644
--- a/configure.ac
+++ b/configure.ac
@@ -167,8 +167,6 @@ if test "x$ac_cv_sys_largefiles" = "xyes"; then
     else
         LIBCDIO_LARGEFILE_FLAGS="-D_LARGE_FILES"
     fi
-    dnl AC_FUNC_FSEEKO sets HAVE_FSEEKO and $ac_cv_sys_largefile_source
-    AC_FUNC_FSEEKO
     if test "$ac_cv_sys_largefile_source" != no; then
         LIBCDIO_LARGEFILE_FLAGS="$LIBDDIO_LARGEFILE_FLAGS 
-D_LARGEFILE_SOURCE=$ac_cv_sys_largefile_source"
     fi
@@ -508,6 +506,19 @@ AC_CHECK_FUNCS( [bzero chdir drand48 ftruncate geteuid 
getgid \
                 seteuid setegid snprintf setenv strndup unsetenv tzset \
                 sleep usleep vsnprintf readlink realpath gmtime_r localtime_r] 
)
 
+# Check for fseeko() support (detection must not rely on LFS)
+AC_MSG_CHECKING([for fseeko])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([
+#ifdef HAVE_SYS_TYPES_H
+#include <sys/types.h> /* for off_t */
+#endif
+#include <stdio.h>
+],[int (*fp) (FILE *, off_t, int) = fseeko;
+return fseeko (stdin, 0, 0) && fp (stdin, 0, 0);])],
+[AC_MSG_RESULT(yes); AC_DEFINE(HAVE_FSEEKO, 1,
+                    [Define to 1 if you have the `fseeko' function.])],
+[AC_MSG_RESULT(no)])
+
 # check for timegm() support
 AC_CHECK_FUNC(timegm, AC_DEFINE(HAVE_TIMEGM,1,
                      [Define to 1 if timegm is available]))
diff --git a/lib/driver/_cdio_stdio.c b/lib/driver/_cdio_stdio.c
index 1a3a1eb..1491d2d 100644
--- a/lib/driver/_cdio_stdio.c
+++ b/lib/driver/_cdio_stdio.c
@@ -123,6 +123,14 @@ static driver_return_code_t
 _stdio_seek(void *p_user_data, off_t i_offset, int whence)
 {
   _UserData *const ud = p_user_data;
+#ifndef HAVE_FSEEKO
+  /* Detect if off_t is lossy-truncated to long to avoid data corruption */
+  if ( (sizeof(off_t) > sizeof(long)) && (i_offset != (off_t)((long)i_offset)) 
) {
+    cdio_error ( STRINGIFY(STDIO_SEEK) " (): lossy truncation detected!");
+    errno = EFBIG;
+    return DRIVER_OP_ERROR;
+  }
+#endif
 
   if ( (i_offset=STDIO_SEEK (ud->fd, i_offset, whence)) ) {
     cdio_error ( STRINGIFY(STDIO_SEEK) " (): %s", strerror (errno));
-- 
1.7.8.msysgit.0