Re: [PATCH v3 19/25] security: Introduce inode_post_remove_acl hook

[Stefan Berger <stefanb@linux.ibm.com>]

On 9/4/23 09:34, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@huawei.com>
>
> In preparation for moving IMA and EVM to the LSM infrastructure, introduce
> the inode_post_remove_acl hook.
>
> It is useful for EVM to recalculate the HMAC on the remaining POSIX ACLs
> and other file metadata, after it verified the HMAC of current file
> metadata with the inode_remove_acl hook.
>
> LSMs should use the new hook instead of inode_remove_acl, when they need to
> know that the operation was done successfully (not known in
> inode_remove_acl). The new hook cannot return an error and cannot cause the
> operation to be reverted.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> ---
>   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 3b7dbea5c3ff..2a2a2750b3e9 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 bba1fbd97207..eedc26790a07 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 556d019ebe5c..e543ae80309b 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -373,6 +373,9 @@ 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);
> @@ -915,6 +918,11 @@ 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 aabace9e24d9..554f4925323d 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2323,6 +2323,23 @@ 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 sec after remove_acl op
> + * @idmap: idmap of the mount
> + * @dentry: file
> + * @acl_name: acl name
> + *
> + * Update inode security field after successful remove_acl operation 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

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>