[PATCH 2/2] nss: handle stat failure in check_reload_and_get (BZ #28752)

[Adhemerval Zanella]

On 25/05/2022 21:20, Sam James via Libc-alpha wrote:
> Skip the chroot test if the database isn't loaded
> correctly (because the chroot test uses some
> existing DB state).
> 
> The __stat64_time64 -> fstatat call can fail if
> running under an (aggressive) seccomp filter,
> like Firefox seems to use.
> 
> This manifested in a crash when using glib built
> with FAM support with such a Firefox build.
> 
> Suggested-by: DJ Delorie <dj@redhat.com>
> Signed-off-by: Sam James <sam@gentoo.org>
> ---
>  nss/nss_database.c | 33 ++++++++++++++++++---------------
>  1 file changed, 18 insertions(+), 15 deletions(-)
> 
> diff --git a/nss/nss_database.c b/nss/nss_database.c
> index d56c5b798d..6c9b440a98 100644
> --- a/nss/nss_database.c
> +++ b/nss/nss_database.c
> @@ -420,21 +420,24 @@ nss_database_check_reload_and_get (struct nss_database_state *local,
>        return true;
>      }
>  
> -  /* Before we reload, verify that "/" hasn't changed.  We assume that
> -     errors here are very unlikely, but the chance that we're entering
> -     a container is also very unlikely, so we err on the side of both
> -     very unlikely things not happening at the same time.  */
> -  if (__stat64_time64 ("/", &str) != 0
> -      || (local->root_ino != 0
> -	  && (str.st_ino != local->root_ino
> -	      ||  str.st_dev != local->root_dev)))
> -    {
> -      /* Change detected; disable reloading and return current state.  */
> -      atomic_store_release (&local->data.reload_disabled, 1);
> -      *result = local->data.services[database_index];
> -      __libc_lock_unlock (local->lock);
> -      return true;
> -    }
> +  if (local->data.services[database_index] != NULL) {
> +      /* Before we reload, verify that "/" hasn't changed.  We assume that
> +        errors here are very unlikely, but the chance that we're entering
> +        a container is also very unlikely, so we err on the side of both
> +        very unlikely things not happening at the same time.  */
> +      if (__stat64_time64 ("/", &str) != 0
> +        || (local->root_ino != 0
> +        && (str.st_ino != local->root_ino
> +            ||  str.st_dev != local->root_dev)))
> +      {
> +        /* Change detected; disable reloading and return current state.  */
> +        atomic_store_release (&local->data.reload_disabled, 1);
> +        *result = local->data.services[database_index];
> +        __libc_lock_unlock (local->lock);
> +        return true;
> +      }
> +  }
> +
>    local->root_ino = str.st_ino;
>    local->root_dev = str.st_dev;
>    __libc_lock_unlock (local->lock);

Besides the buildbot issue [1] you already noted, please use the expected GNU
indentation.  We have now a clang-format script (.clang-format) to help the
format.

[1] https://www.delorie.com/trybots/32bit/9696/nss-tst-reload1.out