Re: [PATCH v5 17/23] security: Introduce inode_post_remove_acl hook

[Casey Schaufler]

On 11/7/2023 5:40 AM, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
>
> In preparation for moving IMA and EVM to the LSM infrastructure, introduce
> the inode_post_remove_acl hook.
>
> At inode_remove_acl hook, EVM verifies the file's existing HMAC value. At
> inode_post_remove_acl, EVM re-calculates the file's HMAC with the passed
> POSIX ACL removed and other file metadata.
>
> Other LSMs could similarly take some action after successful POSIX ACL
> removal.
>
> The new hook cannot return an error and cannot cause the operation to be
> reverted.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>

Acked-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>


> ---
>  fs/posix_acl.c                |  1 +
>  include/linux/lsm_hook_defs.h |  2 ++
>  include/linux/security.h      |  8 ++++++++
>  security/security.c           | 17 +++++++++++++++++
>  4 files changed, 28 insertions(+)
>
> diff --git a/fs/posix_acl.c b/fs/posix_acl.c
> index 58e3c1e2fbbc..e3fbe1a9f3f5 100644
> --- a/fs/posix_acl.c
> +++ b/fs/posix_acl.c
> @@ -1246,6 +1246,7 @@ int vfs_remove_acl(struct mnt_idmap *idmap, struct dentry *dentry,
>  		error = -EIO;
>  	if (!error) {
>  		fsnotify_xattr(dentry);
> +		security_inode_post_remove_acl(idmap, dentry, acl_name);
>  		evm_inode_post_remove_acl(idmap, dentry, acl_name);
>  	}
>  
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index 6a671616196f..2bf128f7cbae 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -163,6 +163,8 @@ LSM_HOOK(int, 0, inode_get_acl, struct mnt_idmap *idmap,
>  	 struct dentry *dentry, const char *acl_name)
>  LSM_HOOK(int, 0, inode_remove_acl, struct mnt_idmap *idmap,
>  	 struct dentry *dentry, const char *acl_name)
> +LSM_HOOK(void, LSM_RET_VOID, inode_post_remove_acl, struct mnt_idmap *idmap,
> +	 struct dentry *dentry, const char *acl_name)
>  LSM_HOOK(int, 0, inode_need_killpriv, struct dentry *dentry)
>  LSM_HOOK(int, 0, inode_killpriv, struct mnt_idmap *idmap,
>  	 struct dentry *dentry)
> diff --git a/include/linux/security.h b/include/linux/security.h
> index d71d0b08e9fe..7cd7126f6545 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -378,6 +378,9 @@ int security_inode_get_acl(struct mnt_idmap *idmap,
>  			   struct dentry *dentry, const char *acl_name);
>  int security_inode_remove_acl(struct mnt_idmap *idmap,
>  			      struct dentry *dentry, const char *acl_name);
> +void security_inode_post_remove_acl(struct mnt_idmap *idmap,
> +				    struct dentry *dentry,
> +				    const char *acl_name);
>  void security_inode_post_setxattr(struct dentry *dentry, const char *name,
>  				  const void *value, size_t size, int flags);
>  int security_inode_getxattr(struct dentry *dentry, const char *name);
> @@ -934,6 +937,11 @@ static inline int security_inode_remove_acl(struct mnt_idmap *idmap,
>  	return 0;
>  }
>  
> +static inline void security_inode_post_remove_acl(struct mnt_idmap *idmap,
> +						  struct dentry *dentry,
> +						  const char *acl_name)
> +{ }
> +
>  static inline void security_inode_post_setxattr(struct dentry *dentry,
>  		const char *name, const void *value, size_t size, int flags)
>  { }
> diff --git a/security/security.c b/security/security.c
> index d2dbea54a63a..6eb7c9cff1e5 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2413,6 +2413,23 @@ int security_inode_remove_acl(struct mnt_idmap *idmap,
>  	return evm_inode_remove_acl(idmap, dentry, acl_name);
>  }
>  
> +/**
> + * security_inode_post_remove_acl() - Update inode security after rm posix acls
> + * @idmap: idmap of the mount
> + * @dentry: file
> + * @acl_name: acl name
> + *
> + * Update inode security data after successfully removing posix acls on
> + * @dentry in @idmap. The posix acls are identified by @acl_name.
> + */
> +void security_inode_post_remove_acl(struct mnt_idmap *idmap,
> +				    struct dentry *dentry, const char *acl_name)
> +{
> +	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
> +		return;
> +	call_void_hook(inode_post_remove_acl, idmap, dentry, acl_name);
> +}
> +
>  /**
>   * security_inode_post_setxattr() - Update the inode after a setxattr operation
>   * @dentry: file