Re: [PATCH v3 18/25] security: Introduce inode_post_set_acl hook

Stefan Berger
2023-09-05T19:42:13Z

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_set_acl hook.
>
> It is useful for EVM to recalculate the HMAC on the modified POSIX ACL and
> other file metadata, after it verified the HMAC of current file metadata
> with the inode_set_acl hook.
>
> LSMs should use the new hook instead of inode_set_acl, when they need to
> know that the operation was done successfully (not known in inode_set_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 | 7 +++++++
> security/security.c | 17 +++++++++++++++++
> 4 files changed, 27 insertions(+)
>
> diff --git a/fs/posix_acl.c b/fs/posix_acl.c
> index 7fa1b738bbab..3b7dbea5c3ff 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 9ae573b83737..bba1fbd97207 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 5f296761883f..556d019ebe5c 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -367,6 +367,8 @@ 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,
> @@ -894,6 +896,11 @@ 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 aa6274c90147..aabace9e24d9 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2260,6 +2260,23 @@ 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 after set_acl()
> + * @dentry: file
> + * @acl_name: acl name
> + * @kacl: acl struct
> + *
> + * Update inode security field after successful set_acl operation 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

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