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



On Tue, Dec 15, 2009 at 08:32:49AM +0100, Jim Meyering wrote:
> 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 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;
>  }
> 
>  /*

  Hum, we need to make sure first that this would work on sysfs
as this is one of the problem raised lately when using that
virFileResolveLink() wrapper on a previous fix.

Daniel

-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/


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