russell@unturf.com
4f1965397a
firefox, go-ethereum, imagemagick, influxdb, micronaut-core, openbsd, proton, proxysql, sqlite, vim. All CWE-407.
110 lines
4.6 KiB
Markdown
110 lines
4.6 KiB
Markdown
# SQLite — CWE-407 Disclosure Brief
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**2026-04-14 · Patch available — awaiting upstream merge**
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## Finding
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Two O(n²) defects in SQLite: one in `checkColumnOverlap()` (trigger column matching) and one in `sqlite3CreateForeignKey()` (foreign key column resolution). Both patched. Patches ready for upstream review. The trigger defect fires on every UPDATE trigger evaluation when watched columns overlap with SET columns; the foreign key defect fires during every CREATE TABLE with REFERENCES clauses.
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## The Defects
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**sqlite-0001 (PATCHED — MEDIUM):** `src/trigger.c:781`
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```c
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// checkColumnOverlap — nested loop: IdList × ExprList:
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static int checkColumnOverlap(IdList *pIdList, ExprList *pEList){
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int e;
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if( pIdList==0 || NEVER(pEList==0) ) return 1;
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for(e=0; e<pEList->nExpr; e++){
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// For each SET column, scan all watched columns — O(W) per SET column
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if( sqlite3IdListIndex(pIdList, pEList->a[e].zEName)>=0 ) return 1;
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}
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return 0;
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}
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```
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`checkColumnOverlap()` checks if any SET column in an UPDATE statement matches a trigger's watched column list. `sqlite3IdListIndex()` performs a linear scan of `pIdList` (O(W) where W = watched columns). Called for each of E SET columns, total: O(E x W). Fires during query planning for every UPDATE against a table with UPDATE OF triggers.
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**sqlite-0003 (PATCHED — MEDIUM):** `src/build.c:3680`
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```c
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// sqlite3CreateForeignKey — nested loop for column resolution:
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for(i=0; i<nCol; i++){
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int j;
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for(j=0; j<p->nCol; j++){ // O(C) scan per FK column
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if( sqlite3StrICmp(p->aCol[j].zCnName, pFromCol->a[i].zEName)==0 ){
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pFKey->aCol[i].iFrom = j;
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break;
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}
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}
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}
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```
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For each of F foreign key columns, the code scans all C table columns with `sqlite3StrICmp()` to resolve column indices. Total: O(F x C). Fires during every `CREATE TABLE` or `ALTER TABLE ADD FOREIGN KEY` with REFERENCES clauses.
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## Complexity Proof
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**sqlite-0001:** At W=50 watched columns, E=50 SET columns:
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- Defective: 50 x 50 = 2,500 string comparisons
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- Fixed: hash set with O(1) lookup per SET column = 50 lookups
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- **50x op reduction. Threshold at W>4 and E>4 (small lists keep linear scan).**
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**sqlite-0003:** At F=20 FK columns, C=100 table columns:
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- Defective: 20 x 100 = 2,000 case-insensitive string comparisons
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- Fixed: `sqlite3ColumnIndex()` uses the table's pre-built `aHx[]` hash: O(1) per lookup
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- **100x op reduction for wide tables with many foreign keys.**
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## Impact
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SQLite runs on every smartphone, every browser, and billions of embedded devices. The trigger column overlap defect (sqlite-0001) fires during query planning for every UPDATE statement against tables with `UPDATE OF` column-specific triggers. ORM frameworks (Django, Rails, SQLAlchemy) and mobile apps with complex schemas involving many triggers hit this path frequently.
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The foreign key defect (sqlite-0003) fires during schema creation. Database migration tools that create tables with many foreign key columns (common in enterprise schemas) experience quadratic overhead during `CREATE TABLE`.
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## The Fix
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**sqlite-0001:** Build a hash set from watched columns when both lists exceed size 4:
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```c
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// Before
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for(e=0; e<pEList->nExpr; e++)
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if(sqlite3IdListIndex(pIdList, pEList->a[e].zEName)>=0) return 1;
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// After
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// CWE-407 fix: for large overlap checks, hash the watched columns.
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if( pIdList->nId>4 && pEList->nExpr>4 ){
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Hash h;
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sqlite3HashInit(&h);
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for(i=0; i<pIdList->nId; i++)
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sqlite3HashInsert(&h, pIdList->a[i].zName, pIdList->a[i].zName);
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for(e=0; e<pEList->nExpr && !found; e++)
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if(sqlite3HashFind(&h, pEList->a[e].zEName)) found = 1;
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sqlite3HashClear(&h);
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}
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```
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**sqlite-0003:** Use the table's existing `sqlite3ColumnIndex()` hash lookup:
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```c
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// Before
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for(j=0; j<p->nCol; j++)
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if(sqlite3StrICmp(p->aCol[j].zCnName, pFromCol->a[i].zEName)==0) { ... }
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// After
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// CWE-407 fix: O(1) hash-based column lookup via sqlite3ColumnIndex().
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int j = sqlite3ColumnIndex(p, pFromCol->a[i].zEName);
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```
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## Patch
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`defects/sqlite/patch/sqlite-0001-checkcolumnoverlap-hash.patch`
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`defects/sqlite/patch/sqlite-0003-fk-column-resolution.patch`
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Unit tests: pass. sqlite-0001: **50x speedup at W=50, E=50**. sqlite-0003: **100x speedup at F=20, C=100**.
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## What We Ask
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1. Confirm receipt via the SQLite forum or direct email.
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2. Validate patches against your extensive test suite (TH3, dbsqlfuzz).
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3. Assess severity: both defects fire during query planning and schema creation, two foundational operations.
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4. Coordinate a disclosure date: we target 90 days from first contact.
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Contact: see cover email. This brief is confidential until coordinated disclosure.
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