On 12/14/2023 9:08 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_removexattr hook.
>
> At inode_removexattr hook, EVM verifies the file's existing HMAC value. At
> inode_post_removexattr, EVM re-calculates the file's HMAC with the passed
> xattr removed and other file metadata.
>
> Other LSMs could similarly take some action after successful xattr removal.
>
> 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>
> Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
Reviewed-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> ---
> fs/xattr.c | 9 +++++----
> include/linux/lsm_hook_defs.h | 2 ++
> include/linux/security.h | 5 +++++
> security/security.c | 14 ++++++++++++++
> 4 files changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/fs/xattr.c b/fs/xattr.c
> index 09d927603433..f891c260a971 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -552,11 +552,12 @@ __vfs_removexattr_locked(struct mnt_idmap *idmap,
> goto out;
>
> error = __vfs_removexattr(idmap, dentry, name);
> + if (error)
> + return error;
>
> - if (!error) {
> - fsnotify_xattr(dentry);
> - evm_inode_post_removexattr(dentry, name);
> - }
> + fsnotify_xattr(dentry);
> + security_inode_post_removexattr(dentry, name);
> + evm_inode_post_removexattr(dentry, name);
>
> out:
> return error;
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index 091cddb4e6de..c3199bb69103 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -149,6 +149,8 @@ LSM_HOOK(int, 0, inode_getxattr, struct dentry *dentry, const char *name)
> LSM_HOOK(int, 0, inode_listxattr, struct dentry *dentry)
> LSM_HOOK(int, 0, inode_removexattr, struct mnt_idmap *idmap,
> struct dentry *dentry, const char *name)
> +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(int, 0, inode_get_acl, struct mnt_idmap *idmap,
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 664df46b22a9..922ea7709bae 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -380,6 +380,7 @@ int security_inode_getxattr(struct dentry *dentry, const char *name);
> int security_inode_listxattr(struct dentry *dentry);
> int security_inode_removexattr(struct mnt_idmap *idmap,
> struct dentry *dentry, const char *name);
> +void security_inode_post_removexattr(struct dentry *dentry, const char *name);
> int security_inode_need_killpriv(struct dentry *dentry);
> int security_inode_killpriv(struct mnt_idmap *idmap, struct dentry *dentry);
> int security_inode_getsecurity(struct mnt_idmap *idmap,
> @@ -940,6 +941,10 @@ static inline int security_inode_removexattr(struct mnt_idmap *idmap,
> return cap_inode_removexattr(idmap, dentry, name);
> }
>
> +static inline void security_inode_post_removexattr(struct dentry *dentry,
> + const char *name)
> +{ }
> +
> static inline int security_inode_need_killpriv(struct dentry *dentry)
> {
> return cap_inode_need_killpriv(dentry);
> diff --git a/security/security.c b/security/security.c
> index ce3bc7642e18..8aa6e9f316dd 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2452,6 +2452,20 @@ int security_inode_removexattr(struct mnt_idmap *idmap,
> return evm_inode_removexattr(idmap, dentry, name);
> }
>
> +/**
> + * security_inode_post_removexattr() - Update the inode after a removexattr op
> + * @dentry: file
> + * @name: xattr name
> + *
> + * Update the inode after a successful removexattr operation.
> + */
> +void security_inode_post_removexattr(struct dentry *dentry, const char *name)
> +{
> + if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
> + return;
> + call_void_hook(inode_post_removexattr, dentry, name);
> +}
> +
> /**
> * security_inode_need_killpriv() - Check if security_inode_killpriv() required
> * @dentry: associated dentry
