[PATCH] overlayfs: Trigger file re-evaluation by IMA / EVM after writes

[Christian Brauner]

On Wed, Apr 05, 2023 at 01:14:49PM -0400, Stefan Berger wrote:
> Overlayfs fails to notify IMA / EVM about file content modifications
> and therefore IMA-appraised files may execute even though their file
> signature does not validate against the changed hash of the file
> anymore. To resolve this issue, add a call to integrity_notify_change()
> to the ovl_release() function to notify the integrity subsystem about
> file changes. The set flag triggers the re-evaluation of the file by
> IMA / EVM once the file is accessed again.
> 
> Signed-off-by: Stefan Berger <stefanb at linux.ibm.com>
> ---
>  fs/overlayfs/file.c       |  4 ++++
>  include/linux/integrity.h |  6 ++++++
>  security/integrity/iint.c | 13 +++++++++++++
>  3 files changed, 23 insertions(+)
> 
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 6011f955436b..19b8f4bcc18c 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -13,6 +13,7 @@
>  #include <linux/security.h>
>  #include <linux/mm.h>
>  #include <linux/fs.h>
> +#include <linux/integrity.h>
>  #include "overlayfs.h"
>  
>  struct ovl_aio_req {
> @@ -169,6 +170,9 @@ static int ovl_open(struct inode *inode, struct file *file)
>  
>  static int ovl_release(struct inode *inode, struct file *file)
>  {
> +	if (file->f_flags & O_ACCMODE)
> +		integrity_notify_change(inode);
> +
>  	fput(file->private_data);
>  
>  	return 0;
> diff --git a/include/linux/integrity.h b/include/linux/integrity.h
> index 2ea0f2f65ab6..cefdeccc1619 100644
> --- a/include/linux/integrity.h
> +++ b/include/linux/integrity.h
> @@ -23,6 +23,7 @@ enum integrity_status {
>  #ifdef CONFIG_INTEGRITY
>  extern struct integrity_iint_cache *integrity_inode_get(struct inode *inode);
>  extern void integrity_inode_free(struct inode *inode);
> +extern void integrity_notify_change(struct inode *inode);

I thought we concluded that ima is going to move into the security hook
infrastructure so it seems this should be a proper LSM hook?