Messages in this thread | | | Date | Mon, 19 Jan 2009 09:56:59 -0500 | From | Paul Clements <> | Subject | Re: nbd: add locking to nbd_ioctl |
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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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