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Comment:On the first connection to a WAL-mode database that was not cleanly shut down and contains a left-over -shm file, truncate the -shm file to 3 bytes instead of to 0 bytes. Avoiding a truncation to 0 means that system monitoring tools can better detect if a process illegitimately tries to truncate a -shm file. Such a rogue process might think it is being helpful by cleaning up old files, but there is a race condition that can cause damage to the database.
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SHA3-256:90cf32cde072a305f30c75a71665d1f9e23e805c0a49f5306f015c056dd70f0c
User & Date: drh 2018-10-11 13:51:48
Context
2018-10-11
16:38
Always reset the pager before changing the codec. check-in: 0bf0fd24 user: drh tags: trunk
13:57
Merge enhancements from trunk. check-in: 9e10d88b user: drh tags: apple-osx
13:51
On the first connection to a WAL-mode database that was not cleanly shut down and contains a left-over -shm file, truncate the -shm file to 3 bytes instead of to 0 bytes. Avoiding a truncation to 0 means that system monitoring tools can better detect if a process illegitimately tries to truncate a -shm file. Such a rogue process might think it is being helpful by cleaning up old files, but there is a race condition that can cause damage to the database. check-in: 90cf32cd user: drh tags: trunk
10:37
In the CLI, fix a file descriptor leak following OOM and a missing va_end() call. check-in: ec36d15a user: drh tags: trunk
Changes
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Changes to src/os_unix.c.

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    rc = SQLITE_IOERR_LOCK;
  }else if( lock.l_type==F_UNLCK ){
    if( pShmNode->isReadonly ){
      pShmNode->isUnlocked = 1;
      rc = SQLITE_READONLY_CANTINIT;
    }else{
      rc = unixShmSystemLock(pDbFd, F_WRLCK, UNIX_SHM_DMS, 1);





      if( rc==SQLITE_OK && robust_ftruncate(pShmNode->hShm, 0) ){
        rc = unixLogError(SQLITE_IOERR_SHMOPEN,"ftruncate",pShmNode->zFilename);
      }
    }
  }else if( lock.l_type==F_WRLCK ){
    rc = SQLITE_BUSY;
  }








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    rc = SQLITE_IOERR_LOCK;
  }else if( lock.l_type==F_UNLCK ){
    if( pShmNode->isReadonly ){
      pShmNode->isUnlocked = 1;
      rc = SQLITE_READONLY_CANTINIT;
    }else{
      rc = unixShmSystemLock(pDbFd, F_WRLCK, UNIX_SHM_DMS, 1);
      /* The first connection to attach must truncate the -shm file.  We
      ** truncate to 3 bytes (an arbitrary small number, less than the
      ** -shm header size) rather than 0 as a system debugging aid, to
      ** help detect if a -shm file truncation is legitimate or is the work
      ** or a rogue process. */
      if( rc==SQLITE_OK && robust_ftruncate(pShmNode->hShm, 3) ){
        rc = unixLogError(SQLITE_IOERR_SHMOPEN,"ftruncate",pShmNode->zFilename);
      }
    }
  }else if( lock.l_type==F_WRLCK ){
    rc = SQLITE_BUSY;
  }