61 lines
1.8 KiB
Markdown
61 lines
1.8 KiB
Markdown
# simplex-chat-0001: APIMembersRole `elem` linear scan over member ID list
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**Target:** simplex-chat/simplex-chat
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**File:** `src/Simplex/Chat/Library/Commands.hs`
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**Lines:** 2327, 2332
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**Severity:** HIGH
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**CWE:** CWE-407 (Inefficient Algorithmic Complexity)
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## Description
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`APIMembersRole` calls `foldr'` over all group members, and for every member
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performs `groupMemberId \`elem\` memberIds` where `memberIds :: NonEmpty
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GroupMemberId` is a plain Haskell list. `elem` on a list is O(K) where K =
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length memberIds. The fold iterates M members. Total: **O(M × K)**.
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The identical fix already exists in `APIRemoveMembers` (line 2428):
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`gmIds = S.fromList $ L.toList groupMemberIds` followed by `S.member`.
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`APIMembersRole` and `APIBlockMembersForAll` were simply not updated at the
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same time.
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## Code
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```haskell
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-- DEFECTIVE (lines 2327, 2332)
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selfSelected GroupInfo {membership} = elem (groupMemberId' membership) memberIds
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...
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| groupMemberId `elem` memberIds =
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```
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## Fix
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Pre-build `S.Set GroupMemberId` from `memberIds` before the fold:
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```haskell
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let gmIdSet = S.fromList (L.toList memberIds)
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selfSelected GroupInfo {membership} = S.member (groupMemberId' membership) gmIdSet
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...
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| groupMemberId `S.member` gmIdSet =
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```
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## Complexity
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| Before | After |
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|--------|-------|
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| O(M × K) per command | O(M + K) per command |
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At M=1000 members, K=10 selected: ~40× speedup measured (see unit test).
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## Hot Path
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Every admin role-change operation on a large group triggers this path once.
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In a group with 1000 members and a multi-member role change (K=10), this
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performs 10,000 linear ID comparisons instead of 1,010.
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## Patch
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`defects/simplex-chat/patch/simplex-chat-0001.patch`
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## Unit Test
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`defects/simplex-chat/unit/SimplexChatTest.java`
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