[Libguestfs] [PATCH] inspect: improve UsrMove detection (RHBZ#1186935)

[Richard W.M. Jones]

On Thu, Mar 17, 2016 at 12:25:18PM +0100, Pino Toscano wrote:
> In case /usr is a symlink to /usr/bin, then we cannot rely on /usr/bin
> to exist, since /usr might be in a different partition.  Thus, in case
> /bin is a symlink, check it points to "usr/bin".
> ---
>  src/inspect-fs.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/src/inspect-fs.c b/src/inspect-fs.c
> index 02fdb2a..0714ae1 100644
> --- a/src/inspect-fs.c
> +++ b/src/inspect-fs.c
> @@ -43,6 +43,7 @@ static int check_filesystem (guestfs_h *g, const char *mountable,
>                               int whole_device);
>  static void extend_fses (guestfs_h *g);
>  static int get_partition_context (guestfs_h *g, const char *partition, int *partnum_ret, int *nr_partitions_ret);
> +static int is_symlink_to (guestfs_h *g, const char *file, const char *wanted_target);
>  
>  /* Find out if 'device' contains a filesystem.  If it does, add
>   * another entry in g->fses.
> @@ -215,8 +216,7 @@ check_filesystem (guestfs_h *g, const char *mountable,
>    /* Linux root? */
>    else if (is_dir_etc &&
>             (is_dir_bin ||
> -            (guestfs_is_symlink (g, "/bin") > 0 &&
> -             guestfs_is_dir (g, "/usr/bin") > 0)) &&
> +            is_symlink_to (g, "/bin", "usr/bin") > 0) &&
>             guestfs_is_file (g, "/etc/fstab") > 0) {
>      fs->is_root = 1;
>      fs->format = OS_FORMAT_INSTALLED;
> @@ -366,6 +366,22 @@ get_partition_context (guestfs_h *g, const char *partition,
>    return 0;
>  }
>  
> +static int
> +is_symlink_to (guestfs_h *g, const char *file, const char *wanted_target)
> +{
> +  CLEANUP_FREE char *target = NULL;
> +
> +  if (guestfs_is_symlink (g, file) == 0)
> +    return 0;
> +
> +  target = guestfs_readlink (g, file);
> +  /* This should not fail, but play safe. */
> +  if (target == NULL)
> +    return 0;
> +
> +  return STREQ (target, wanted_target);
> +}
> +
>  int
>  guestfs_int_is_file_nocase (guestfs_h *g, const char *path)
>  {

Yup, pretty good solution.  ACK.

However, worth checking what Debian is doing now, since they
implemented UsrMove madness just recently.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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