From 7225abddeefb569f1f2da739211d7797b63814a2 Mon Sep 17 00:00:00 2001
From: George Goldberg <george@gberg.me>
Date: Mon, 28 May 2018 14:46:52 +0100
Subject: MM-8814: Remove implicit permission grants from post ownership.
 (#8391)

---
 api4/post.go         | 41 +++++++++++++++++++++++++++++++++++------
 app/authorization.go | 13 -------------
 2 files changed, 35 insertions(+), 19 deletions(-)

diff --git a/api4/post.go b/api4/post.go
index 189edfc20..b4392a74e 100644
--- a/api4/post.go
+++ b/api4/post.go
@@ -246,11 +246,24 @@ func deletePost(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if !c.App.SessionHasPermissionToPost(c.Session, c.Params.PostId, model.PERMISSION_DELETE_OTHERS_POSTS) {
-		c.SetPermissionError(model.PERMISSION_DELETE_OTHERS_POSTS)
+	post, err := c.App.GetSinglePost(c.Params.PostId)
+	if err != nil {
+		c.SetPermissionError(model.PERMISSION_DELETE_POST)
 		return
 	}
 
+	if c.Session.UserId == post.UserId {
+		if !c.App.SessionHasPermissionToChannel(c.Session, post.ChannelId, model.PERMISSION_DELETE_POST) {
+			c.SetPermissionError(model.PERMISSION_DELETE_POST)
+			return
+		}
+	} else {
+		if !c.App.SessionHasPermissionToChannel(c.Session, post.ChannelId, model.PERMISSION_DELETE_OTHERS_POSTS) {
+			c.SetPermissionError(model.PERMISSION_DELETE_OTHERS_POSTS)
+			return
+		}
+	}
+
 	if _, err := c.App.DeletePost(c.Params.PostId); err != nil {
 		c.Err = err
 		return
@@ -364,11 +377,19 @@ func updatePost(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if !c.App.SessionHasPermissionToPost(c.Session, c.Params.PostId, model.PERMISSION_EDIT_OTHERS_POSTS) {
-		c.SetPermissionError(model.PERMISSION_EDIT_OTHERS_POSTS)
+	originalPost, err := c.App.GetSinglePost(c.Params.PostId)
+	if err != nil {
+		c.SetPermissionError(model.PERMISSION_EDIT_POST)
 		return
 	}
 
+	if c.Session.UserId != originalPost.UserId {
+		if !c.App.SessionHasPermissionToChannelByPost(c.Session, c.Params.PostId, model.PERMISSION_EDIT_OTHERS_POSTS) {
+			c.SetPermissionError(model.PERMISSION_EDIT_OTHERS_POSTS)
+			return
+		}
+	}
+
 	post.Id = c.Params.PostId
 
 	rpost, err := c.App.UpdatePost(c.App.PostWithProxyRemovedFromImageURLs(post), false)
@@ -398,11 +419,19 @@ func patchPost(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if !c.App.SessionHasPermissionToPost(c.Session, c.Params.PostId, model.PERMISSION_EDIT_OTHERS_POSTS) {
-		c.SetPermissionError(model.PERMISSION_EDIT_OTHERS_POSTS)
+	originalPost, err := c.App.GetSinglePost(c.Params.PostId)
+	if err != nil {
+		c.SetPermissionError(model.PERMISSION_EDIT_POST)
 		return
 	}
 
+	if c.Session.UserId != originalPost.UserId {
+		if !c.App.SessionHasPermissionToChannelByPost(c.Session, c.Params.PostId, model.PERMISSION_EDIT_OTHERS_POSTS) {
+			c.SetPermissionError(model.PERMISSION_EDIT_OTHERS_POSTS)
+			return
+		}
+	}
+
 	patchedPost, err := c.App.PatchPost(c.Params.PostId, c.App.PostPatchWithProxyRemovedFromImageURLs(post))
 	if err != nil {
 		c.Err = err
diff --git a/app/authorization.go b/app/authorization.go
index 57a38c199..3de50e27b 100644
--- a/app/authorization.go
+++ b/app/authorization.go
@@ -94,19 +94,6 @@ func (a *App) SessionHasPermissionToUser(session model.Session, userId string) b
 	return false
 }
 
-func (a *App) SessionHasPermissionToPost(session model.Session, postId string, permission *model.Permission) bool {
-	post, err := a.GetSinglePost(postId)
-	if err != nil {
-		return false
-	}
-
-	if post.UserId == session.UserId {
-		return true
-	}
-
-	return a.SessionHasPermissionToChannel(session, post.ChannelId, permission)
-}
-
 func (a *App) HasPermissionTo(askingUserId string, permission *model.Permission) bool {
 	user, err := a.GetUser(askingUserId)
 	if err != nil {
-- 
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