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Overview
Comment:Fix a problem in the memdb vfs xLock() function allowing clients to upgrade to EXCLUSIVE locks when other connections are holding SHARED.
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Timelines: family | ancestors | descendants | both | branch-3.40
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SHA3-256: d18cce37b5b73bb2a4f28eb1b55eb2c3ffe1fc23c921c13170af3d74a549f48e
User & Date: drh 2022-12-05 14:23:06
Context
2022-12-26
15:21
Fix an infinite loop in the MEMSYS5 auxiliary memory allocator that occurs for memory allocations between 500MiB and 1GiB in size. Error introduced by check-in [949133231f8f751a]. The problem only affects builds that include the SQLITE_ENABLE_MEMSYS5 compile-time option. (check-in: c10d40ca user: drh tags: branch-3.40)
2022-12-05
14:23
Fix a problem in the memdb vfs xLock() function allowing clients to upgrade to EXCLUSIVE locks when other connections are holding SHARED. (check-in: d18cce37 user: drh tags: branch-3.40)
14:20
Regenerate the configure script so that it includes the correct patch number. (check-in: e2ae2ea1 user: drh tags: branch-3.40)
14:12
Fix a problem in the memdb vfs xLock() function allowing clients to upgrade to EXCLUSIVE locks when other connections are holding SHARED. Forum post 5adb92e2baca3678. (check-in: 15f0be8a user: dan tags: trunk)
Changes
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Changes to src/memdb.c.

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static int memdbLock(sqlite3_file *pFile, int eLock){
  MemFile *pThis = (MemFile*)pFile;
  MemStore *p = pThis->pStore;
  int rc = SQLITE_OK;
  if( eLock==pThis->eLock ) return SQLITE_OK;
  memdbEnter(p);
  if( eLock>SQLITE_LOCK_SHARED ){

    if( p->mFlags & SQLITE_DESERIALIZE_READONLY ){
      rc = SQLITE_READONLY;










    }else if( pThis->eLock<=SQLITE_LOCK_SHARED ){


      if( p->nWrLock ){
        rc = SQLITE_BUSY;
      }else{
        p->nWrLock = 1;
      }
    }
  }else if( eLock==SQLITE_LOCK_SHARED ){








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static int memdbLock(sqlite3_file *pFile, int eLock){
  MemFile *pThis = (MemFile*)pFile;
  MemStore *p = pThis->pStore;
  int rc = SQLITE_OK;
  if( eLock==pThis->eLock ) return SQLITE_OK;
  memdbEnter(p);
  if( eLock>SQLITE_LOCK_SHARED ){
    assert( pThis->eLock>=SQLITE_LOCK_SHARED );
    if( p->mFlags & SQLITE_DESERIALIZE_READONLY ){
      rc = SQLITE_READONLY;
    }else if( eLock==SQLITE_LOCK_EXCLUSIVE ){
      /* Taking an EXCLUSIVE lock. Fail if we only have SHARED and any
      ** other client has any kind of write-lock. Also fail if any other
      ** client is holding read-lock. */
      if( pThis->eLock<=SQLITE_LOCK_SHARED && p->nWrLock ){
        rc = SQLITE_BUSY;
      }else if( p->nRdLock>1 ){
        rc = SQLITE_BUSY;
      }
      p->nWrLock = 1;
    }else if( pThis->eLock<=SQLITE_LOCK_SHARED ){
      /* Upgrading to RESERVED or PENDING from SHARED. Fail if any other
      ** client has a write-lock of any kind.  */
      if( p->nWrLock ){
        rc = SQLITE_BUSY;
      }else{
        p->nWrLock = 1;
      }
    }
  }else if( eLock==SQLITE_LOCK_SHARED ){
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