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

Stefan Berger
2023-09-05T18:36:59Z

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_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@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@linux.ibm.com>