[PATCH v3 12/25] security: Introduce inode_post_setattr hook

[Stefan Berger]

On 9/4/23 09:34, Roberto Sassu wrote:

> From: Roberto Sassu <roberto.sassu at huawei.com>
>
> In preparation for moving IMA and EVM to the LSM infrastructure, introduce
> the inode_post_setattr hook.
>
> It is useful for EVM to recalculate the HMAC on modified file attributes
> and other file metadata, after it verified the HMAC of current file
> metadata with the inode_setattr hook.
>
> LSMs should use the new hook instead of inode_setattr, when they need to
> know that the operation was done successfully (not known in inode_setattr).
> The new hook cannot return an error and cannot cause the operation to be
> reverted.
>
> Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
> ---
>   fs/attr.c                     |  1 +
>   include/linux/lsm_hook_defs.h |  2 ++
>   include/linux/security.h      |  7 +++++++
>   security/security.c           | 16 ++++++++++++++++
>   4 files changed, 26 insertions(+)
>
> diff --git a/fs/attr.c b/fs/attr.c
> index 431f667726c7..3c309eb456c6 100644
> --- a/fs/attr.c
> +++ b/fs/attr.c
> @@ -486,6 +486,7 @@ int notify_change(struct mnt_idmap *idmap, struct dentry *dentry,
>   
>   	if (!error) {
>   		fsnotify_change(dentry, ia_valid);
> +		security_inode_post_setattr(idmap, dentry, ia_valid);
>   		ima_inode_post_setattr(idmap, dentry, ia_valid);
>   		evm_inode_post_setattr(idmap, dentry, ia_valid);
>   	}
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index fdf075a6b1bb..995d30336cfa 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -136,6 +136,8 @@ LSM_HOOK(int, 0, inode_follow_link, struct dentry *dentry, struct inode *inode,
>   LSM_HOOK(int, 0, inode_permission, struct inode *inode, int mask)
>   LSM_HOOK(int, 0, inode_setattr, struct mnt_idmap *idmap, struct dentry *dentry,
>   	 struct iattr *attr)
> +LSM_HOOK(void, LSM_RET_VOID, inode_post_setattr, struct mnt_idmap *idmap,
> +	 struct dentry *dentry, int ia_valid)
>   LSM_HOOK(int, 0, inode_getattr, const struct path *path)
>   LSM_HOOK(int, 0, inode_setxattr, struct mnt_idmap *idmap,
>   	 struct dentry *dentry, const char *name, const void *value,
> diff --git a/include/linux/security.h b/include/linux/security.h
> index dcb3604ffab8..820899db5276 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -355,6 +355,8 @@ int security_inode_follow_link(struct dentry *dentry, struct inode *inode,
>   int security_inode_permission(struct inode *inode, int mask);
>   int security_inode_setattr(struct mnt_idmap *idmap,
>   			   struct dentry *dentry, struct iattr *attr);
> +void security_inode_post_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
> +				 int ia_valid);
>   int security_inode_getattr(const struct path *path);
>   int security_inode_setxattr(struct mnt_idmap *idmap,
>   			    struct dentry *dentry, const char *name,
> @@ -856,6 +858,11 @@ static inline int security_inode_setattr(struct mnt_idmap *idmap,
>   	return 0;
>   }
>   
> +static inline void
> +security_inode_post_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
> +			    int ia_valid)
> +{ }

Existing security_sem_free() and others are also formatted like it, so 
it should be ok.


> +
>   static inline int security_inode_getattr(const struct path *path)
>   {
>   	return 0;
> diff --git a/security/security.c b/security/security.c
> index 2b24d01cf181..764a6f28b3b9 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2124,6 +2124,22 @@ int security_inode_setattr(struct mnt_idmap *idmap,
>   }
>   EXPORT_SYMBOL_GPL(security_inode_setattr);
>   
> +/**
> + * security_inode_post_setattr() - Update the inode after a setattr operation
> + * @idmap: idmap of the mount
> + * @dentry: file
> + * @ia_valid: file attributes set
> + *
> + * Update inode security field after successful setting file attributes.
> + */
> +void security_inode_post_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
> +				 int ia_valid)
> +{
> +	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
> +		return;
> +	call_void_hook(inode_post_setattr, idmap, dentry, ia_valid);
> +}
> +
>   /**
>    * security_inode_getattr() - Check if getting file attributes is allowed
>    * @path: file

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