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SubjectRe: nbd: add locking to nbd_ioctl
Pavel Machek wrote:
>> Pavel Machek wrote:
>>> On Fri 2009-01-16 10:24:06, Paul Clements wrote:

>> lo->sock is only modified under tx_lock (except for SET_SOCK, where the
>> device is being initialized, in which case it's impossible for any other
>> thread to be accessing the device)
>
> Well, unless the user is evil or confused? :-).

Even in that case, you're just going to get EBUSY. Nothing bad will
happen. SET_SOCK checks for lo->file, so it cannot be called on an
active nbd device.


>> As for other fields, I assume you're talking about blksize, et al.
>> Taking tx_lock doesn't prevent you from screwing yourself if you modify
>> those while the device is active. You'd need to disallow those ioctls
>> when the device is active (check lo->file). Again, this is only going to
>> happen if you really misuse the ioctls.
>
> Ok, I'll take a look at the missing checks. I'd really like to make
> this "stable" -- no amount of misuse should crash the kernel.

Just to summarize, I don't think we need to hold tx_lock around the
entirety of nbd_ioctl. We do need one extra tx_lock around xmit_timeout
and we do need to check for lo->file and return EBUSY in all of the
SET_*SIZE* ioctls.

Thanks,
Paul



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