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Comment:Fix a segfault that could occur if a non-empty in-memory database was the destination of a backup operation from a database with a smaller page size. Forum post 679b4de86e763d52.
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SHA3-256: 020968f857d7b90bab3525fc9d6b859a019f6a80422c3d5ffb88f5bdb8e02a11
User & Date: dan 2023-04-19 17:07:35
Original Comment: Fix a segfault that could occur if a non-empty in-memory database was the destination of a backup operation from a database with a smaller page size.
Context
2023-04-19
18:32
Remove unreachable legacy code. (check-in: e3e7fb87 user: drh tags: trunk)
17:13
Fix a segfault that could occur if a non-empty in-memory database was the destination of a backup operation from a database with a smaller page size. (check-in: d3724158 user: drh tags: branch-3.41)
17:07
Fix a segfault that could occur if a non-empty in-memory database was the destination of a backup operation from a database with a smaller page size. Forum post 679b4de86e763d52. (check-in: 020968f8 user: dan tags: trunk)
15:35
Do not remove pages from the cache of an in-memory database due to a failure to acquire the page due to it being larger than the maximum page size. Fix for forum post a19bb49140. (check-in: 982b3556 user: drh tags: trunk)
Changes
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Changes to src/backup.c.

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  i64 iOff;

  assert( sqlite3BtreeGetReserveNoMutex(p->pSrc)>=0 );
  assert( p->bDestLocked );
  assert( !isFatalError(p->rc) );
  assert( iSrcPg!=PENDING_BYTE_PAGE(p->pSrc->pBt) );
  assert( zSrcData );

  /* Catch the case where the destination is an in-memory database and the
  ** page sizes of the source and destination differ. 
  */
  if( nSrcPgsz!=nDestPgsz && sqlite3PagerIsMemdb(pDestPager) ){
    rc = SQLITE_READONLY;
  }

  /* This loop runs once for each destination page spanned by the source 
  ** page. For each iteration, variable iOff is set to the byte offset
  ** of the destination page.
  */
  for(iOff=iEnd-(i64)nSrcPgsz; rc==SQLITE_OK && iOff<iEnd; iOff+=nDestPgsz){
    DbPage *pDestPg = 0;








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  i64 iOff;

  assert( sqlite3BtreeGetReserveNoMutex(p->pSrc)>=0 );
  assert( p->bDestLocked );
  assert( !isFatalError(p->rc) );
  assert( iSrcPg!=PENDING_BYTE_PAGE(p->pSrc->pBt) );
  assert( zSrcData );




  assert( nSrcPgsz==nDestPgsz || sqlite3PagerIsMemdb(pDestPager)==0 );



  /* This loop runs once for each destination page spanned by the source 
  ** page. For each iteration, variable iOff is set to the byte offset
  ** of the destination page.
  */
  for(iOff=iEnd-(i64)nSrcPgsz; rc==SQLITE_OK && iOff<iEnd; iOff+=nDestPgsz){
    DbPage *pDestPg = 0;
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    }

    /* Do not allow backup if the destination database is in WAL mode
    ** and the page sizes are different between source and destination */
    pgszSrc = sqlite3BtreeGetPageSize(p->pSrc);
    pgszDest = sqlite3BtreeGetPageSize(p->pDest);
    destMode = sqlite3PagerGetJournalMode(sqlite3BtreePager(p->pDest));
    if( SQLITE_OK==rc && destMode==PAGER_JOURNALMODE_WAL && pgszSrc!=pgszDest ){



      rc = SQLITE_READONLY;
    }
  
    /* Now that there is a read-lock on the source database, query the
    ** source pager for the number of pages in the database.
    */
    nSrcPage = (int)sqlite3BtreeLastPage(p->pSrc);








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    }

    /* Do not allow backup if the destination database is in WAL mode
    ** and the page sizes are different between source and destination */
    pgszSrc = sqlite3BtreeGetPageSize(p->pSrc);
    pgszDest = sqlite3BtreeGetPageSize(p->pDest);
    destMode = sqlite3PagerGetJournalMode(sqlite3BtreePager(p->pDest));
    if( SQLITE_OK==rc 
     && (destMode==PAGER_JOURNALMODE_WAL || sqlite3PagerIsMemdb(pDestPager))
     && pgszSrc!=pgszDest 
    ){
      rc = SQLITE_READONLY;
    }
  
    /* Now that there is a read-lock on the source database, query the
    ** source pager for the number of pages in the database.
    */
    nSrcPage = (int)sqlite3BtreeLastPage(p->pSrc);
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Changes to test/backup.test.

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#
do_test backup-11.1 {
  sqlite3 db1 :memory:
  sqlite3 db2 :memory:
  sqlite3_backup B db1 main db2 temp
  B finish
} {SQLITE_OK}
























finish_test








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#
do_test backup-11.1 {
  sqlite3 db1 :memory:
  sqlite3 db2 :memory:
  sqlite3_backup B db1 main db2 temp
  B finish
} {SQLITE_OK}
db1 close
db2 close

#-------------------------------------------------------------------------
do_test backup-12.1 {
  sqlite3 db1 :memory:
  sqlite3 db2 :memory:
  db1 eval {
    PRAGMA page_size = 8192;
    CREATE TABLE t1(x);
  }
  db2 eval {
    PRAGMA page_size = 1024;
    CREATE TABLE t2(x);
  }

  sqlite3_backup B db1 main db2 temp
  B step 100
  B finish
} {SQLITE_READONLY}




finish_test