[libvirt] [PATCH] avoid malfunction when virFileResolveLink is applied to non-POSIX FS

[Jim Meyering]

Without this patch, virFileResolveLink could misbehave
when applied to a file on a POSIX-nonconforming file system.

The fix is to use gnulib's areadlink module, but it's GPL'd.
I'm ready to relax it to LGPLv2+, and have asked the other author
for his rubber stamp.  Once that's fixed, this change will depend
on having an up-to-date gnulib submodule.  That will be the subject of
my next message.

>From a3133b2e8b1453578b30e4b9c83c7473feb7c65b Mon Sep 17 00:00:00 2001
From: Jim Meyering <meyering at redhat.com>
Date: Tue, 15 Dec 2009 08:27:53 +0100
Subject: [PATCH] avoid malfunction when virFileResolveLink is applied to non-POSIX FS

The virFileResolveLink utility function relied on the POSIX guarantee
that stat.st_size of a symlink is the length of the value.  However,
on some types of file systems, it is invalid, so do not rely on it.
Use gnulib's areadlink module instead.
* bootstrap (modules): Add areadlink.
* src/util/util.c: Include "areadlink.h".
Let areadlink perform the readlink and malloc.
* configure.in (AC_CHECK_FUNCS): Remove readlink.  No need,
since it's presence is guaranteed by gnulib.
---
 bootstrap       |    1 +
 configure.in    |    2 +-
 src/util/util.c |   27 +++------------------------
 3 files changed, 5 insertions(+), 25 deletions(-)

diff --git a/bootstrap b/bootstrap
index 667af4f..c07d851 100755
--- a/bootstrap
+++ b/bootstrap
@@ -65,6 +65,7 @@ gnulib_tool=$GNULIB_SRCDIR/gnulib-tool
 <$gnulib_tool || exit

 modules='
+areadlink
 base64
 c-ctype
 close
diff --git a/configure.in b/configure.in
index 6135932..6ed2efd 100644
--- a/configure.in
+++ b/configure.in
@@ -83,7 +83,7 @@ dnl Use --disable-largefile if you don't want this.
 AC_SYS_LARGEFILE

 dnl Availability of various common functions (non-fatal if missing).
-AC_CHECK_FUNCS([cfmakeraw regexec uname sched_getaffinity getuid getgid posix_fallocate mmap readlink])
+AC_CHECK_FUNCS([cfmakeraw regexec uname sched_getaffinity getuid getgid posix_fallocate mmap])

 dnl Availability of various not common threadsafe functions
 AC_CHECK_FUNCS([strerror_r strtok_r getmntent_r getgrnam_r getpwuid_r])
diff --git a/src/util/util.c b/src/util/util.c
index 694838a..44a4b2f 100644
--- a/src/util/util.c
+++ b/src/util/util.c
@@ -64,6 +64,7 @@
 #include <mntent.h>
 #endif

+#include "areadlink.h"
 #include "virterror_internal.h"
 #include "logging.h"
 #include "event.h"
@@ -1059,10 +1060,7 @@ int virFileLinkPointsTo(const char *checkLink,
 int virFileResolveLink(const char *linkpath,
                        char **resultpath)
 {
-#ifdef HAVE_READLINK
     struct stat st;
-    char *buf;
-    int n;

     *resultpath = NULL;

@@ -1075,28 +1073,9 @@ int virFileResolveLink(const char *linkpath,
         return 0;
     }

-    /* Posix says that 'st_size' field from
-     * result of an lstat() call is filled with
-     * number of bytes in the destination
-     * filename.
-     */
-    if (VIR_ALLOC_N(buf, st.st_size + 1) < 0)
-        return -ENOMEM;
-
-    if ((n = readlink(linkpath, buf, st.st_size)) < 0) {
-        VIR_FREE(buf);
-        return -errno;
-    }
-
-    buf[n] = '\0';
+    *resultpath = areadlink (linkpath);

-    *resultpath = buf;
-    return 0;
-#else
-    if (!(*resultpath = strdup(linkpath)))
-        return -ENOMEM;
-    return 0;
-#endif
+    return *resultpath == NULL ? -1 : 0;
 }

 /*
--
1.6.6.rc2.275.g51e2d