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From: Terry Lambert <terry@lambert.org>
Newsgroups: comp.unix.bsd.freebsd.misc,comp.os.linux.development.system
Subject: Re: The better (more suitable)Unix?? FreeBSD or Linux
Date: 24 Feb 1996 20:19:20 GMT
Organization: Utah Valley State College, Orem, Utah
Lines: 34
Message-ID: <4gnrs8$i5h@park.uvsc.edu>
References: <4er9hp$5ng@orb.direct.ca> <4g5k95$28m@park.uvsc.edu> <4ggol0$38h@pell.pell.chi.il.us> <4giebg$70o@park.uvsc.edu> <4glfoq$4lo@pell.pell.chi.il.us>
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Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:15022 comp.os.linux.development.system:18834
orc@pell.chi.il.us (Orc) wrote:
] Okay, but what about the situation of:
]
] 1) I have a file foo that contains sensitive information in blocks
] A, B, C.
]
] 2) I delete this file; the metadata is updated.
Including the bitmap marking the blocks as unallocated.
] 3) Someone else creates a new file bar, and writes a block to it.
] The metadata is written immediately, and is assigned block A.
] The data, being async, is saved to be written when it's
] convenient. (Say the elevator is going down, and the
] metadata lives at block X while the data's at X+n, and
] the metadata is pushed out when the elevator is X <
] elevator < X+n.)
]
] 4) I press the Big Red Switch.
Since the bitmap is not updated until *after* the async writes
have taken place, the blocks being unassigned takes precedence
over their reference by the file "bar", the blocks are not
allocated in the bitmap.
When the drive is fsck'ed, the blocks are unassigned and the file
truncated. No security breach occurs.
Terry Lambert
terry@cs.weber.edu
---
Any opinions in this posting are my own and not those of my present
or previous employers.