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Overview
Comment:Early detection of implausibly sized records to avoid unnecessary large memory allocations.
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SHA3-256:2c8769c69f301307db6663adb8b7c0b89f5959516bf6110cb8ff4b21bd903f70
User & Date: drh 2019-02-04 21:10:24
Context
2019-02-05
08:55
Update test file "resetdb.test" so that it works with the "prepare" permutation. check-in: 95d33812 user: dan tags: trunk
2019-02-04
21:10
Early detection of implausibly sized records to avoid unnecessary large memory allocations. check-in: 2c8769c6 user: drh tags: trunk
19:52
Mention the new -memtrace command-line option in the -help output of the CLI. check-in: ada91aef user: drh tags: trunk
Changes
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Changes to src/btree.c.

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*/
u32 sqlite3BtreePayloadSize(BtCursor *pCur){
  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  getCellInfo(pCur);
  return pCur->info.nPayload;
}




















/*
** Given the page number of an overflow page in the database (parameter
** ovfl), this function finds the page number of the next page in the 
** linked list of overflow pages. If possible, it uses the auto-vacuum
** pointer-map data instead of reading the content of page ovfl to do so. 
**







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*/
u32 sqlite3BtreePayloadSize(BtCursor *pCur){
  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  getCellInfo(pCur);
  return pCur->info.nPayload;
}

/*
** Return an upper bound on the size of any record for the table
** that the cursor is pointing into.
**
** This is an optimization.  Everything will still work if this
** routine always returns 2147483647 (which is the largest record
** that SQLite can handle) or more.  But returning a smaller value might
** prevent large memory allocations when trying to interpret a
** corrupt datrabase.
**
** The current implementation merely returns the size of the underlying
** database file.
*/
sqlite3_int64 sqlite3BtreeMaxRecordSize(BtCursor *pCur){
  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  return pCur->pBt->pageSize * (sqlite3_int64)pCur->pBt->nPage;
}

/*
** Given the page number of an overflow page in the database (parameter
** ovfl), this function finds the page number of the next page in the 
** linked list of overflow pages. If possible, it uses the auto-vacuum
** pointer-map data instead of reading the content of page ovfl to do so. 
**

Changes to src/btree.h.

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i64 sqlite3BtreeIntegerKey(BtCursor*);
#ifdef SQLITE_ENABLE_OFFSET_SQL_FUNC
i64 sqlite3BtreeOffset(BtCursor*);
#endif
int sqlite3BtreePayload(BtCursor*, u32 offset, u32 amt, void*);
const void *sqlite3BtreePayloadFetch(BtCursor*, u32 *pAmt);
u32 sqlite3BtreePayloadSize(BtCursor*);


char *sqlite3BtreeIntegrityCheck(Btree*, int *aRoot, int nRoot, int, int*);
struct Pager *sqlite3BtreePager(Btree*);
i64 sqlite3BtreeRowCountEst(BtCursor*);

#ifndef SQLITE_OMIT_INCRBLOB
int sqlite3BtreePayloadChecked(BtCursor*, u32 offset, u32 amt, void*);







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i64 sqlite3BtreeIntegerKey(BtCursor*);
#ifdef SQLITE_ENABLE_OFFSET_SQL_FUNC
i64 sqlite3BtreeOffset(BtCursor*);
#endif
int sqlite3BtreePayload(BtCursor*, u32 offset, u32 amt, void*);
const void *sqlite3BtreePayloadFetch(BtCursor*, u32 *pAmt);
u32 sqlite3BtreePayloadSize(BtCursor*);
sqlite3_int64 sqlite3BtreeMaxRecordSize(BtCursor*);

char *sqlite3BtreeIntegrityCheck(Btree*, int *aRoot, int nRoot, int, int*);
struct Pager *sqlite3BtreePager(Btree*);
i64 sqlite3BtreeRowCountEst(BtCursor*);

#ifndef SQLITE_OMIT_INCRBLOB
int sqlite3BtreePayloadChecked(BtCursor*, u32 offset, u32 amt, void*);

Changes to src/vdbemem.c.

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  BtCursor *pCur,   /* Cursor pointing at record to retrieve. */
  u32 offset,       /* Offset from the start of data to return bytes from. */
  u32 amt,          /* Number of bytes to return. */
  Mem *pMem         /* OUT: Return data in this Mem structure. */
){
  int rc;
  pMem->flags = MEM_Null;



  if( SQLITE_OK==(rc = sqlite3VdbeMemClearAndResize(pMem, amt+1)) ){
    rc = sqlite3BtreePayload(pCur, offset, amt, pMem->z);
    if( rc==SQLITE_OK ){
      pMem->z[amt] = 0;   /* Overrun area used when reading malformed records */
      pMem->flags = MEM_Blob;
      pMem->n = (int)amt;
    }else{







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  BtCursor *pCur,   /* Cursor pointing at record to retrieve. */
  u32 offset,       /* Offset from the start of data to return bytes from. */
  u32 amt,          /* Number of bytes to return. */
  Mem *pMem         /* OUT: Return data in this Mem structure. */
){
  int rc;
  pMem->flags = MEM_Null;
  if( sqlite3BtreeMaxRecordSize(pCur)<offset+amt ){
    return SQLITE_CORRUPT_BKPT;
  }
  if( SQLITE_OK==(rc = sqlite3VdbeMemClearAndResize(pMem, amt+1)) ){
    rc = sqlite3BtreePayload(pCur, offset, amt, pMem->z);
    if( rc==SQLITE_OK ){
      pMem->z[amt] = 0;   /* Overrun area used when reading malformed records */
      pMem->flags = MEM_Blob;
      pMem->n = (int)amt;
    }else{