Re: [PATCH 2/3] ima: Ensure lock is held when setting iint pointer in inode security blob

[Paul Moore]

On Tue, Oct 8, 2024 at 12:57 PM Roberto Sassu
<roberto.sassu@xxxxxxxxxxxxxxx> wrote:
>
> From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
>
> IMA stores a pointer of the ima_iint_cache structure, containing integrity
> metadata, in the inode security blob. However, check and assignment of this
> pointer is not atomic, and it might happen that two tasks both see that the
> iint pointer is NULL and try to set it, causing a memory leak.
>
> Ensure that the iint check and assignment is guarded, by adding a lockdep
> assertion in ima_inode_get().
>
> Consequently, guard the remaining ima_inode_get() calls, in
> ima_post_create_tmpfile() and ima_post_path_mknod(), to avoid the lockdep
> warnings.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> ---
>  security/integrity/ima/ima_iint.c |  5 +++++
>  security/integrity/ima/ima_main.c | 14 ++++++++++++--
>  2 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/security/integrity/ima/ima_iint.c b/security/integrity/ima/ima_iint.c
> index c176fd0faae7..fe676ccec32f 100644
> --- a/security/integrity/ima/ima_iint.c
> +++ b/security/integrity/ima/ima_iint.c
> @@ -87,8 +87,13 @@ static void ima_iint_free(struct ima_iint_cache *iint)
>   */
>  struct ima_iint_cache *ima_inode_get(struct inode *inode)
>  {
> +       struct ima_iint_cache_lock *iint_lock;
>         struct ima_iint_cache *iint;
>
> +       iint_lock = ima_inode_security(inode->i_security);
> +       if (iint_lock)
> +               lockdep_assert_held(&iint_lock->mutex);
> +
>         iint = ima_iint_find(inode);
>         if (iint)
>                 return iint;

Can you avoid the ima_iint_find() call here and just do the following?

  /* not sure if you need to check !iint_lock or not? */
  if (!iint_lock)
    return NULL;
  iint = iint_lock->iint;
  if (!iint)
    return NULL;

-- 
paul-moore.com