Thread (47 messages) 47 messages, 6 authors, 2024-07-23

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

From: Serge Hallyn <serge@hallyn.com>
Date: 2024-07-11 13:55:13
Also in: bpf, linux-integrity, linux-kselftest, linux-security-module, selinux

Jul 11, 2024 06:14:08 Xu Kuohai [off-list ref]:
From: Xu Kuohai <redacted>

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.
quoted hunk ↗ jump to hunk
Signed-off-by: Xu Kuohai <redacted>
---
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
  
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