Re: [PATCH v5 16/23] security: Introduce inode_post_set_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_set_acl hook.
>
> At inode_set_acl hook, EVM verifies the file's existing HMAC value. At
> inode_post_set_acl, EVM re-calculates the file's HMAC based on the modified
> POSIX ACL and other file metadata.
>
> Other LSMs could similarly take some action after successful POSIX ACL
> change.
>
> 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      |  7 +++++++
>  security/security.c           | 17 +++++++++++++++++
>  4 files changed, 27 insertions(+)
>
> diff --git a/fs/posix_acl.c b/fs/posix_acl.c
> index a05fe94970ce..58e3c1e2fbbc 100644
> --- a/fs/posix_acl.c
> +++ b/fs/posix_acl.c
> @@ -1137,6 +1137,7 @@ int vfs_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
>  		error = -EIO;
>  	if (!error) {
>  		fsnotify_xattr(dentry);
> +		security_inode_post_set_acl(dentry, acl_name, kacl);
>  		evm_inode_post_set_acl(dentry, acl_name, kacl);
>  	}
>  
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index ec5319ec2e85..6a671616196f 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -157,6 +157,8 @@ LSM_HOOK(void, LSM_RET_VOID, inode_post_removexattr, struct dentry *dentry,
>  	 const char *name)
>  LSM_HOOK(int, 0, inode_set_acl, struct mnt_idmap *idmap,
>  	 struct dentry *dentry, const char *acl_name, struct posix_acl *kacl)
> +LSM_HOOK(void, LSM_RET_VOID, inode_post_set_acl, struct dentry *dentry,
> +	 const char *acl_name, struct posix_acl *kacl)
>  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,
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 0c85f0337a9e..d71d0b08e9fe 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -372,6 +372,8 @@ int security_inode_setxattr(struct mnt_idmap *idmap,
>  int security_inode_set_acl(struct mnt_idmap *idmap,
>  			   struct dentry *dentry, const char *acl_name,
>  			   struct posix_acl *kacl);
> +void security_inode_post_set_acl(struct dentry *dentry, const char *acl_name,
> +				 struct posix_acl *kacl);
>  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,
> @@ -913,6 +915,11 @@ static inline int security_inode_set_acl(struct mnt_idmap *idmap,
>  	return 0;
>  }
>  
> +static inline void security_inode_post_set_acl(struct dentry *dentry,
> +					       const char *acl_name,
> +					       struct posix_acl *kacl)
> +{ }
> +
>  static inline int security_inode_get_acl(struct mnt_idmap *idmap,
>  					 struct dentry *dentry,
>  					 const char *acl_name)
> diff --git a/security/security.c b/security/security.c
> index ca650c285fd9..d2dbea54a63a 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2350,6 +2350,23 @@ int security_inode_set_acl(struct mnt_idmap *idmap,
>  	return evm_inode_set_acl(idmap, dentry, acl_name, kacl);
>  }
>  
> +/**
> + * security_inode_post_set_acl() - Update inode security from posix acls set
> + * @dentry: file
> + * @acl_name: acl name
> + * @kacl: acl struct
> + *
> + * Update inode security data after successfully setting posix acls on @dentry.
> + * The posix acls in @kacl are identified by @acl_name.
> + */
> +void security_inode_post_set_acl(struct dentry *dentry, const char *acl_name,
> +				 struct posix_acl *kacl)
> +{
> +	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
> +		return;
> +	call_void_hook(inode_post_set_acl, dentry, acl_name, kacl);
> +}
> +
>  /**
>   * security_inode_get_acl() - Check if reading posix acls is allowed
>   * @idmap: idmap of the mount