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Hi! > Yes, and that is exactly the difference between having a side effect > on the open(2), versus having the effect as a result of a write(2). > > Unfortunately, there are already some cases where an open > on a device can have unexpected results. If you don't want > to get blocked waiting for the carrier-detect signal from the > modem when opening a tty device, you had better specify the > O_NONBLOCK option on the open. If you don't want this flag > to be active during the actual I/O operations, then you would > have to do an fcntl to clear the O_NONBLOCK again after the open. > > So I guess things have already been a bit messy in this > area for many years, even before linux even existed, and > in some cases you can't really do anything about it because > the behaviour is mandated by the applicable standards, like > POSIX, SUS, or whatever. > (The blocking of the open on a tty device is explicitly > documented in my copy of the X/Open specification.) > > Fortunately, blocking the nightly backup program by making it > accidentally open a tty is not quite as catastrophic as having > it start a nuclear war, or format the disks, or something, > just because a user was playing games with symlinks. Maybe not *as* catastrophic, but security hole, anyway. User should not be able to block system backups. Small demonstration for bugtraq, anyone? Pavel -- I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care." Panos Katsaloulis describing me w.r.t. patents at discuss@linmodems.org - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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