Re: [PATCH bpf-next v4 01/20] lsm: Refactor return value of LSM hook vm_enough_memory

[Serge Hallyn <serge@hallyn.com>]

Jul 11, 2024 06:14:08 Xu Kuohai <xukuohai@huaweicloud.com>:

> From: Xu Kuohai <xukuohai@huawei.com>
>
> To be consistent with most LSM hooks, convert the return value of
> hook vm_enough_memory to 0 or a negative error code.
>
> Before:
> - Hook vm_enough_memory returns 1 if permission is granted, 0 if not.
> - LSM_RET_DEFAULT(vm_enough_memory_mm) is 1.
>
> After:
> - Hook vm_enough_memory reutrns 0 if permission is granted, negative
>   error code if not.
> - LSM_RET_DEFAULT(vm_enough_memory_mm) is 0.

I haven't done a detailed review yet, but based on the description this is definitely a good change.  Thank you.

> Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
> ---
> include/linux/lsm_hook_defs.h |  2 +-
> include/linux/security.h      |  2 +-
> security/commoncap.c          | 11 +++--------
> security/security.c           | 11 +++++------
> security/selinux/hooks.c      | 15 ++++-----------
> 5 files changed, 14 insertions(+), 27 deletions(-)
>
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index 44488b1ab9a9..e6e6f8473955 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -48,7 +48,7 @@ LSM_HOOK(int, 0, quota_on, struct dentry *dentry)
> LSM_HOOK(int, 0, syslog, int type)
> LSM_HOOK(int, 0, settime, const struct timespec64 *ts,
>      const struct timezone *tz)
> -LSM_HOOK(int, 1, vm_enough_memory, struct mm_struct *mm, long pages)
> +LSM_HOOK(int, 0, vm_enough_memory, struct mm_struct *mm, long pages)
> LSM_HOOK(int, 0, bprm_creds_for_exec, struct linux_binprm *bprm)
> LSM_HOOK(int, 0, bprm_creds_from_file, struct linux_binprm *bprm, const struct file *file)
> LSM_HOOK(int, 0, bprm_check_security, struct linux_binprm *bprm)
> diff --git a/include/linux/security.h b/include/linux/security.h
> index de3af33e6ff5..454f96307cb9 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -634,7 +634,7 @@ static inline int security_settime64(const struct timespec64 *ts,
>
> static inline int security_vm_enough_memory_mm(struct mm_struct *mm, long pages)
> {
> -   return __vm_enough_memory(mm, pages, cap_vm_enough_memory(mm, pages));
> +   return __vm_enough_memory(mm, pages, !cap_vm_enough_memory(mm, pages));
> }
>
> static inline int security_bprm_creds_for_exec(struct linux_binprm *bprm)
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 162d96b3a676..cefad323a0b1 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -1396,17 +1396,12 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
>   * Determine whether the allocation of a new virtual mapping by the current
>   * task is permitted.
>   *
> - * Return: 1 if permission is granted, 0 if not.
> + * Return: 0 if permission granted, negative error code if not.
>   */
> int cap_vm_enough_memory(struct mm_struct *mm, long pages)
> {
> -   int cap_sys_admin = 0;
> -
> -   if (cap_capable(current_cred(), &init_user_ns,
> -               CAP_SYS_ADMIN, CAP_OPT_NOAUDIT) == 0)
> -       cap_sys_admin = 1;
> -
> -   return cap_sys_admin;
> +   return cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN,
> +              CAP_OPT_NOAUDIT);
> }
>
> /**
> diff --git a/security/security.c b/security/security.c
> index e5ca08789f74..3475f0cab3da 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1115,15 +1115,14 @@ int security_vm_enough_memory_mm(struct mm_struct *mm, long pages)
>     int rc;
>
>     /*
> -    * The module will respond with a positive value if
> -    * it thinks the __vm_enough_memory() call should be
> -    * made with the cap_sys_admin set. If all of the modules
> -    * agree that it should be set it will. If any module
> -    * thinks it should not be set it won't.
> +    * The module will respond with 0 if it thinks the __vm_enough_memory()
> +    * call should be made with the cap_sys_admin set. If all of the modules
> +    * agree that it should be set it will. If any module thinks it should
> +    * not be set it won't.
>      */
>     hlist_for_each_entry(hp, &security_hook_heads.vm_enough_memory, list) {
>         rc = hp->hook.vm_enough_memory(mm, pages);
> -       if (rc <= 0) {
> +       if (rc < 0) {
>             cap_sys_admin = 0;
>             break;
>         }
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 7eed331e90f0..9cd5a8f1f6a3 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2202,23 +2202,16 @@ static int selinux_syslog(int type)
> }
>
> /*
> - * Check that a process has enough memory to allocate a new virtual
> - * mapping. 0 means there is enough memory for the allocation to
> - * succeed and -ENOMEM implies there is not.
> + * Check permission for allocating a new virtual mapping. Returns
> + * 0 if permission is granted, negative error code if not.
>   *
>   * Do not audit the selinux permission check, as this is applied to all
>   * processes that allocate mappings.
>   */
> static int selinux_vm_enough_memory(struct mm_struct *mm, long pages)
> {
> -   int rc, cap_sys_admin = 0;
> -
> -   rc = cred_has_capability(current_cred(), CAP_SYS_ADMIN,
> -                CAP_OPT_NOAUDIT, true);
> -   if (rc == 0)
> -       cap_sys_admin = 1;
> -
> -   return cap_sys_admin;
> +   return cred_has_capability(current_cred(), CAP_SYS_ADMIN,
> +                  CAP_OPT_NOAUDIT, true);
> }
>
> /* binprm security operations */
> --
> 2.30.2