Commit message: When an error occurs while rewriting the parser tree for window functions
in the sqlite3WindowRewrite() routine, make sure that pParse->nErr is set,
and make sure that this shuts down any subsequent code generation that might
depend on the transformations that were implemented.  This fixes a problem
discovered by the Yongheng and Rui fuzzer.

FossilOrigin-Name: e2bddcd4c55ba3cbe0130332679ff4b048630d0ced9a8899982edb5a3569ba7f
CVE: CVE-2019-19924
CWE: CWE-755
Vulnerability description: SQLite 3.30.1 mishandles certain parser-tree rewriting, related to expr.c, vdbeaux.c, and window.c. This is caused by incorrect sqlite3WindowRewrite() error handling.

Project: sqlite
File: expr.c

static int codeCompare(
  Parse *pParse,    /* The parsing (and code generating) context */
  Expr *pLeft,      /* The left operand */
  Expr *pRight,     /* The right operand */
  int opcode,       /* The comparison opcode */
  int in1, int in2, /* Register holding operands */
  int dest,         /* Jump here if true.  */
  int jumpIfNull,   /* If true, jump if either operand is NULL */
  int isCommuted    /* The comparison has been commuted */
){
  int p5;
  int addr;
  CollSeq *p4;

  if( isCommuted ){
    p4 = sqlite3BinaryCompareCollSeq(pParse, pRight, pLeft);
  }else{
    p4 = sqlite3BinaryCompareCollSeq(pParse, pLeft, pRight);
  }
  p5 = binaryCompareP5(pLeft, pRight, jumpIfNull);
  addr = sqlite3VdbeAddOp4(pParse->pVdbe, opcode, in2, dest, in1,
                           (void*)p4, P4_COLLSEQ);
  sqlite3VdbeChangeP5(pParse->pVdbe, (u8)p5);
  return addr;
}

Project: sqlite
File: vdbeaux.c

static void vdbeVComment(Vdbe *p, const char *zFormat, va_list ap){
  assert( p->nOp>0 || p->aOp==0 );
  assert( p->aOp==0 || p->aOp[p->nOp-1].zComment==0 || p->db->mallocFailed );
  if( p->nOp ){
    assert( p->aOp );
    sqlite3DbFree(p->db, p->aOp[p->nOp-1].zComment);
    p->aOp[p->nOp-1].zComment = sqlite3VMPrintf(p->db, zFormat, ap);
  }
}

Project: sqlite
File: window.c

int sqlite3WindowRewrite(Parse *pParse, Select *p){
  int rc = SQLITE_OK;
  if( p->pWin && p->pPrior==0 && (p->selFlags & SF_WinRewrite)==0 ){
    Vdbe *v = sqlite3GetVdbe(pParse);
    sqlite3 *db = pParse->db;
    Select *pSub = 0;             /* The subquery */
    SrcList *pSrc = p->pSrc;
    Expr *pWhere = p->pWhere;
    ExprList *pGroupBy = p->pGroupBy;
    Expr *pHaving = p->pHaving;
    ExprList *pSort = 0;

    ExprList *pSublist = 0;       /* Expression list for sub-query */
    Window *pMWin = p->pWin;      /* Master window object */
    Window *pWin;                 /* Window object iterator */
    Table *pTab;

    pTab = sqlite3DbMallocZero(db, sizeof(Table));
    if( pTab==0 ){
      return SQLITE_NOMEM;
    }

    p->pSrc = 0;
    p->pWhere = 0;
    p->pGroupBy = 0;
    p->pHaving = 0;
    p->selFlags &= ~SF_Aggregate;
    p->selFlags |= SF_WinRewrite;

    /* Create the ORDER BY clause for the sub-select. This is the concatenation
    ** of the window PARTITION and ORDER BY clauses. Then, if this makes it
    ** redundant, remove the ORDER BY from the parent SELECT.  */
    pSort = sqlite3ExprListDup(db, pMWin->pPartition, 0);
    pSort = exprListAppendList(pParse, pSort, pMWin->pOrderBy, 1);
    if( pSort && p->pOrderBy && p->pOrderBy->nExpr<=pSort->nExpr ){
      int nSave = pSort->nExpr;
      pSort->nExpr = p->pOrderBy->nExpr;
      if( sqlite3ExprListCompare(pSort, p->pOrderBy, -1)==0 ){
        sqlite3ExprListDelete(db, p->pOrderBy);
        p->pOrderBy = 0;
      }
      pSort->nExpr = nSave;
    }

    /* Assign a cursor number for the ephemeral table used to buffer rows.
    ** The OpenEphemeral instruction is coded later, after it is known how
    ** many columns the table will have.  */
    pMWin->iEphCsr = pParse->nTab++;
    pParse->nTab += 3;

    selectWindowRewriteEList(pParse, pMWin, pSrc, p->pEList, pTab, &pSublist);
    selectWindowRewriteEList(pParse, pMWin, pSrc, p->pOrderBy, pTab, &pSublist);
    pMWin->nBufferCol = (pSublist ? pSublist->nExpr : 0);

    /* Append the PARTITION BY and ORDER BY expressions to the to the 
    ** sub-select expression list. They are required to figure out where 
    ** boundaries for partitions and sets of peer rows lie.  */
    pSublist = exprListAppendList(pParse, pSublist, pMWin->pPartition, 0);
    pSublist = exprListAppendList(pParse, pSublist, pMWin->pOrderBy, 0);

    /* Append the arguments passed to each window function to the
    ** sub-select expression list. Also allocate two registers for each
    ** window function - one for the accumulator, another for interim
    ** results.  */
    for(pWin=pMWin; pWin; pWin=pWin->pNextWin){
      ExprList *pArgs = pWin->pOwner->x.pList;
      if( pWin->pFunc->funcFlags & SQLITE_FUNC_SUBTYPE ){
        selectWindowRewriteEList(pParse, pMWin, pSrc, pArgs, pTab, &pSublist);
        pWin->iArgCol = (pSublist ? pSublist->nExpr : 0);
        pWin->bExprArgs = 1;
      }else{
        pWin->iArgCol = (pSublist ? pSublist->nExpr : 0);
        pSublist = exprListAppendList(pParse, pSublist, pArgs, 0);
      }
      if( pWin->pFilter ){
        Expr *pFilter = sqlite3ExprDup(db, pWin->pFilter, 0);
        pSublist = sqlite3ExprListAppend(pParse, pSublist, pFilter);
      }
      pWin->regAccum = ++pParse->nMem;
      pWin->regResult = ++pParse->nMem;
      sqlite3VdbeAddOp2(v, OP_Null, 0, pWin->regAccum);
    }

    /* If there is no ORDER BY or PARTITION BY clause, and the window
    ** function accepts zero arguments, and there are no other columns
    ** selected (e.g. "SELECT row_number() OVER () FROM t1"), it is possible
    ** that pSublist is still NULL here. Add a constant expression here to 
    ** keep everything legal in this case. 
    */
    if( pSublist==0 ){
      pSublist = sqlite3ExprListAppend(pParse, 0, 
        sqlite3Expr(db, TK_INTEGER, "0")
      );
    }

    pSub = sqlite3SelectNew(
        pParse, pSublist, pSrc, pWhere, pGroupBy, pHaving, pSort, 0, 0
    );
    p->pSrc = sqlite3SrcListAppend(pParse, 0, 0, 0);
    if( p->pSrc ){
      Table *pTab2;
      p->pSrc->a[0].pSelect = pSub;
      sqlite3SrcListAssignCursors(pParse, p->pSrc);
      pSub->selFlags |= SF_Expanded;
      pTab2 = sqlite3ResultSetOfSelect(pParse, pSub, SQLITE_AFF_NONE);
      if( pTab2==0 ){
        rc = SQLITE_NOMEM;
      }else{
        memcpy(pTab, pTab2, sizeof(Table));
        pTab->tabFlags |= TF_Ephemeral;
        p->pSrc->a[0].pTab = pTab;
        pTab = pTab2;
      }
      sqlite3VdbeAddOp2(v, OP_OpenEphemeral, pMWin->iEphCsr, pSublist->nExpr);
      sqlite3VdbeAddOp2(v, OP_OpenDup, pMWin->iEphCsr+1, pMWin->iEphCsr);
      sqlite3VdbeAddOp2(v, OP_OpenDup, pMWin->iEphCsr+2, pMWin->iEphCsr);
      sqlite3VdbeAddOp2(v, OP_OpenDup, pMWin->iEphCsr+3, pMWin->iEphCsr);
    }else{
      sqlite3SelectDelete(db, pSub);
    }
    if( db->mallocFailed ) rc = SQLITE_NOMEM;
    sqlite3DbFree(db, pTab);
  }

  return rc;
}