[libvirt] [PATCH] virt-aa-helper: better write denials handling

[Guido Günther]

Hi,
On Mon, Jan 18, 2016 at 01:45:08PM +0100, Cédric Bosdonnat wrote:
> Better fix replacing c726af2d: introducing an 'R' permission to
> add read rule, but no explicit deny write rule.
> ---
>  src/security/virt-aa-helper.c | 20 +++++++++++++++++---
>  1 file changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/src/security/virt-aa-helper.c b/src/security/virt-aa-helper.c
> index a2d7226..d0c5246 100644
> --- a/src/security/virt-aa-helper.c
> +++ b/src/security/virt-aa-helper.c
> @@ -785,12 +785,18 @@ get_definition(vahControl * ctl, const char *xmlStr)
>      return rc;
>  }
>  
> +/**
> +  * The permissions allowed are apparmor valid permissions and 'R'. 'R' stands for
> +  * read with no explicit deny rule.
> +  */
>  static int
>  vah_add_path(virBufferPtr buf, const char *path, const char *perms, bool recursive)
>  {
>      char *tmp = NULL;
>      int rc = -1;
>      bool readonly = true;
> +    bool explicit_deny_rule = true;
> +    char *sub = NULL;
>  
>      if (path == NULL)
>          return rc;
> @@ -815,8 +821,16 @@ vah_add_path(virBufferPtr buf, const char *path, const char *perms, bool recursi
>          return rc;
>      }
>  
> -    if (strchr(perms, 'w') != NULL)
> +    if (strchr(perms, 'w') != NULL) {
>          readonly = false;
> +        explicit_deny_rule = false;
> +    }
> +
> +    if ((sub = strchr(perms, 'R')) != NULL) {
> +        /* Don't write the invalid R permission, replace it with 'r' */
> +        sub[0] = 'r';
> +        explicit_deny_rule = false;
> +    }
>  
>      rc = valid_path(tmp, readonly);
>      if (rc != 0) {
> @@ -831,7 +845,7 @@ vah_add_path(virBufferPtr buf, const char *path, const char *perms, bool recursi
>          tmp[strlen(tmp) - 1] = '\0';
>  
>      virBufferAsprintf(buf, "  \"%s%s\" %s,\n", tmp, recursive ? "/**" : "", perms);
> -    if (readonly) {
> +    if (explicit_deny_rule) {
>          virBufferAddLit(buf, "  # don't audit writes to readonly files\n");
>          virBufferAsprintf(buf, "  deny \"%s%s\" w,\n", tmp, recursive ? "/**" : "");
>      }
> @@ -1130,7 +1144,7 @@ get_files(vahControl * ctl)
>              /* We don't need to add deny rw rules for readonly mounts,
>               * this can only lead to troubles when mounting / readonly.
>               */
> -            if (vah_add_path(&buf, fs->src, "rw", true) != 0)
> +            if (vah_add_path(&buf, fs->src, fs->readonly ? "R" : "rw", true) != 0)
>                  goto cleanup;
>          }
>      }

this looks good to me but it would be great to have Jamie's input on
that.
Ceers,
 -- Guido