[libvirt] [PATCH] virt-aa-helper: resolve yet to be created paths

[Michal Privoznik]

On 03/01/2018 03:53 PM, Christian Ehrhardt wrote:
> In certain cases a xml contains paths that do not yet exist, but
> are valid as qemu will create them later on - for example
> vhostuser mode=server sockets.
> 
> In any such cases so far the check to virFileExists failed and due to
> that the paths stayed non-resolved in regard to symlinks.
> 
> But for apparmor those non-resolved rules are non functional as they
> are evaluated after resolving any symlinks.
> 
> Therefore for non-existent files and partially non-existent paths
> resolve as much as possible to get valid rules.
> 
> Example:
>    <interface type='vhostuser'>
>        <model type='virtio'/>
>        <source type='unix'
>                path='/var/run/symlinknet'
>                mode='server'/>

Don't be afraid to write this on one line. Firstly, the 80 character
line is just a soft limit, secondly I like to see verbatim text
unchanged. But feel free to keep it as it is. Your call.

>    </interface>
> 
> Got rendered as:
>   "/var/run/symlinknet" rw,
> 
> But correct with "/var/run" being a symlink to "/run" is:
>   "/run/symlinknet" rw,
> 
> Signed-off-by: Christian Ehrhardt <christian.ehrhardt at canonical.com>
> ---
>  src/security/virt-aa-helper.c | 45 ++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 38 insertions(+), 7 deletions(-)
> 
> diff --git a/src/security/virt-aa-helper.c b/src/security/virt-aa-helper.c
> index ff0068c..91bc339 100644
> --- a/src/security/virt-aa-helper.c
> +++ b/src/security/virt-aa-helper.c
> @@ -41,6 +41,7 @@
>  #include "viralloc.h"
>  #include "vircommand.h"
>  #include "virlog.h"
> +#include "dirname.h"
>  #include "driver.h"
>  
>  #include "security_driver.h"
> @@ -752,6 +753,9 @@ vah_add_path(virBufferPtr buf, const char *path, const char *perms, bool recursi
>      bool explicit_deny_rule = true;
>      char *sub = NULL;
>      char *perms_new = NULL;
> +    char *pathdir = NULL;
> +    char *pathtmp = NULL;
> +    char *pathreal = NULL;
>  
>      if (path == NULL)
>          return rc;
> @@ -766,14 +770,38 @@ vah_add_path(virBufferPtr buf, const char *path, const char *perms, bool recursi
>          return 0;
>      }
>  
> -    if (virFileExists(path)) {
> -        if ((tmp = realpath(path, NULL)) == NULL) {
> -            vah_error(NULL, 0, path);
> -            vah_error(NULL, 0, _("could not find realpath for disk"));
> -            return rc;
> +    /* files might be created by qemu later on and not exist right now.
> +     * But realpath needs a valid path to work on, therefore:
> +     * 1. walk the path to find longest valid path
> +     * 2. get the realpath of that valid path
> +     * 3. re-combine the realpath with the remaining suffix
> +     * Note: A totally non existent path is used as-is
> +     */
> +    if ((pathdir = mdir_name(path)) == NULL)
> +        goto cleanup;
> +    while (!virFileExists(pathdir)) {
> +        if (VIR_STRDUP_QUIET(pathtmp, pathdir) < 0)
> +            goto cleanup;
> +        VIR_FREE(pathdir);
> +        if ((pathdir = mdir_name(pathtmp)) == NULL)
> +            goto cleanup;
> +        VIR_FREE(pathtmp);
> +    }

I guess this can be written simpler:

  if ((pathdir = mdir_name(path)) == NULL)
      goto cleanup;
  while (!virFileExists(pathdir)) {
      if ((pathtmp = mdir_name(pathdir)) == NULL)
          goto cleanup;
      VIR_FREE(pathdir);
      VIR_STEAL_PTR(pathdir, pathtmp);
  }


ACK whether you decide to go with my way (untested though) or what you
have. Sorry for the delay.

Michal