[PATCH bpf-next v4 02/20] lsm: Refactor return value of LSM hook inode_need_killpriv

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From: Xu Kuohai <xukuohai@xxxxxxxxxx>

To be consistent with most LSM hooks, convert the return value of
hook inode_need_killpriv to 0 or a negative error code.

Before:
- Both hook inode_need_killpriv and func security_inode_need_killpriv
  return > 0 if security_inode_killpriv is required, 0 if not, and < 0
  to abort the operation.

After:
- Both hook inode_need_killpriv and func security_inode_need_killpriv
  return 0 on success and a negative error code on failure.
  On success, hook inode_need_killpriv sets output param @need to true
  if security_inode_killpriv is required, and false if not. When @need
  is true, func security_inode_need_killpriv sets ATTR_KILL_PRIV flag
  in @attr; when false, it clears the flag.
  On failure, @need and @attr remains unchanged.

Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
---
 fs/attr.c                     |  5 ++---
 fs/inode.c                    |  4 +---
 include/linux/lsm_hook_defs.h |  2 +-
 include/linux/security.h      | 20 ++++++++++++++++----
 security/commoncap.c          | 12 ++++++++----
 security/security.c           | 29 ++++++++++++++++++++++++-----
 6 files changed, 52 insertions(+), 20 deletions(-)

diff --git a/fs/attr.c b/fs/attr.c
index 960a310581eb..aaadc721c982 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -427,11 +427,10 @@ int notify_change(struct mnt_idmap *idmap, struct dentry *dentry,
 		attr->ia_mtime = timestamp_truncate(attr->ia_mtime, inode);
 
 	if (ia_valid & ATTR_KILL_PRIV) {
-		error = security_inode_need_killpriv(dentry);
+		error = security_inode_need_killpriv(dentry, &ia_valid);
 		if (error < 0)
 			return error;
-		if (error == 0)
-			ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
+		attr->ia_valid = ia_valid;
 	}
 
 	/*
diff --git a/fs/inode.c b/fs/inode.c
index 3a41f83a4ba5..cd335dc3a3bc 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2012,11 +2012,9 @@ int dentry_needs_remove_privs(struct mnt_idmap *idmap,
 		return 0;
 
 	mask = setattr_should_drop_suidgid(idmap, inode);
-	ret = security_inode_need_killpriv(dentry);
+	ret = security_inode_need_killpriv(dentry, &mask);
 	if (ret < 0)
 		return ret;
-	if (ret)
-		mask |= ATTR_KILL_PRIV;
 	return mask;
 }
 
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index e6e6f8473955..964849de424b 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -165,7 +165,7 @@ LSM_HOOK(int, 0, inode_remove_acl, struct mnt_idmap *idmap,
 	 struct dentry *dentry, const char *acl_name)
 LSM_HOOK(void, LSM_RET_VOID, inode_post_remove_acl, struct mnt_idmap *idmap,
 	 struct dentry *dentry, const char *acl_name)
-LSM_HOOK(int, 0, inode_need_killpriv, struct dentry *dentry)
+LSM_HOOK(int, 0, inode_need_killpriv, struct dentry *dentry, bool *need)
 LSM_HOOK(int, 0, inode_killpriv, struct mnt_idmap *idmap,
 	 struct dentry *dentry)
 LSM_HOOK(int, -EOPNOTSUPP, inode_getsecurity, struct mnt_idmap *idmap,
diff --git a/include/linux/security.h b/include/linux/security.h
index 454f96307cb9..1614ef5b2dd2 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -161,7 +161,7 @@ int cap_inode_setxattr(struct dentry *dentry, const char *name,
 		       const void *value, size_t size, int flags);
 int cap_inode_removexattr(struct mnt_idmap *idmap,
 			  struct dentry *dentry, const char *name);
-int cap_inode_need_killpriv(struct dentry *dentry);
+int cap_inode_need_killpriv(struct dentry *dentry, bool *need);
 int cap_inode_killpriv(struct mnt_idmap *idmap, struct dentry *dentry);
 int cap_inode_getsecurity(struct mnt_idmap *idmap,
 			  struct inode *inode, const char *name, void **buffer,
@@ -389,7 +389,7 @@ 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_need_killpriv(struct dentry *dentry, int *attr);
 int security_inode_killpriv(struct mnt_idmap *idmap, struct dentry *dentry);
 int security_inode_getsecurity(struct mnt_idmap *idmap,
 			       struct inode *inode, const char *name,
@@ -971,9 +971,21 @@ static inline void security_inode_post_removexattr(struct dentry *dentry,
 						   const char *name)
 { }
 
-static inline int security_inode_need_killpriv(struct dentry *dentry)
+static inline int security_inode_need_killpriv(struct dentry *dentry, int *attr)
 {
-	return cap_inode_need_killpriv(dentry);
+	int rc;
+	bool need = false;
+
+	rc = cap_inode_need_killpriv(dentry, &need);
+	if (rc < 0)
+		return rc;
+
+	if (need)
+		*attr |= ATTR_KILL_PRIV;
+	else
+		*attr &= ~ATTR_KILL_PRIV;
+
+	return 0;
 }
 
 static inline int security_inode_killpriv(struct mnt_idmap *idmap,
diff --git a/security/commoncap.c b/security/commoncap.c
index cefad323a0b1..17d6188d22cf 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -286,21 +286,25 @@ int cap_capset(struct cred *new,
 /**
  * cap_inode_need_killpriv - Determine if inode change affects privileges
  * @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV
+ * @need: If inode_killpriv() is needed
  *
  * Determine if an inode having a change applied that's marked ATTR_KILL_PRIV
  * affects the security markings on that inode, and if it is, should
  * inode_killpriv() be invoked or the change rejected.
  *
- * Return: 1 if security.capability has a value, meaning inode_killpriv()
- * is required, 0 otherwise, meaning inode_killpriv() is not required.
+ * Return: Always returns 0. If security.capability has a value, meaning
+ * inode_killpriv() is required, @need is set to true.
  */
-int cap_inode_need_killpriv(struct dentry *dentry)
+int cap_inode_need_killpriv(struct dentry *dentry, bool *need)
 {
 	struct inode *inode = d_backing_inode(dentry);
 	int error;
 
 	error = __vfs_getxattr(dentry, inode, XATTR_NAME_CAPS, NULL, 0);
-	return error > 0;
+	if (error > 0)
+		*need = true;
+
+	return 0;
 }
 
 /**
diff --git a/security/security.c b/security/security.c
index 3475f0cab3da..a4abcd86eb36 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2490,17 +2490,36 @@ void security_inode_post_removexattr(struct dentry *dentry, const char *name)
 /**
  * security_inode_need_killpriv() - Check if security_inode_killpriv() required
  * @dentry: associated dentry
+ * @attr: attribute flags
  *
  * Called when an inode has been changed to determine if
  * security_inode_killpriv() should be called.
  *
- * Return: Return <0 on error to abort the inode change operation, return 0 if
- *         security_inode_killpriv() does not need to be called, return >0 if
- *         security_inode_killpriv() does need to be called.
+ * Return: Return 0 on success, negative error code on failure.
+ *         On success, set ATTR_KILL_PRIV flag in @attr when @need is true,
+ *         clears it when false.
  */
-int security_inode_need_killpriv(struct dentry *dentry)
+int security_inode_need_killpriv(struct dentry *dentry, int *attr)
 {
-	return call_int_hook(inode_need_killpriv, dentry);
+	int rc;
+	bool need = false;
+	struct security_hook_list *hp;
+
+	hlist_for_each_entry(hp, &security_hook_heads.inode_need_killpriv,
+			     list) {
+		rc = hp->hook.inode_need_killpriv(dentry, &need);
+		if (rc < 0)
+			return rc;
+		if (need)
+			break;
+	}
+
+	if (need)
+		*attr |= ATTR_KILL_PRIV;
+	else
+		*attr &= ~ATTR_KILL_PRIV;
+
+	return 0;
 }
 
 /**
-- 
2.30.2





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