Messages in this thread | | | Date | Tue, 15 Dec 2015 15:41:41 -0200 | From | "Herton R. Krzesinski" <> | Subject | Re: pty: fix use after free/oops at pty_unix98_shutdown |
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On Tue, Dec 15, 2015 at 09:28:28AM -0800, Peter Hurley wrote: > On 12/15/2015 08:36 AM, Herton R. Krzesinski wrote: > > On Tue, Dec 15, 2015 at 08:17:56AM -0800, Peter Hurley wrote: > >>> I also expect in a rare case where all ptmx references are gone/closed, this also > >>> could happen on final close when the master tty is given to pty_unix98_shutdown. > >> > >> This logic I'm not following. If the pty master is being released, then the inode > >> is valid for the release() operation in-progress. > > > > Hi Peter, > > > > yes, you're right if you are eg. closing the /dev/ptmx or /dev/pts/ptmx file > > previously opened. But I thought and refer above to the case where for example > > you are closing /dev/tty and that's the final close and there is no other > > process in the system with the /dev/{,*/}ptmx opened, the inode which referenced > > the previously opened ptmx could be gone. It would be rare though since in a > > running system any logged in user eg. through ssh or with a terminal open in X > > will have at least a ptmx device opened. > > /dev/tty can never be an alias for /dev/ptmx in Linux: a master pty cannot be > a controlling terminal. So if the master pty is being released it will always be > with the /dev/ptmx inode.
Indeed, pty_unix98_shutdown in case of /dev/tty close will be called with slave pty tty_struct. Sorry about my previous confusing/wrong statement. My concern is only valid in case final /dev/tty close used the ptmx inode instead of slave_inode created at ptmx_open, which was not the case before/with current code, but is the case when applying my patch, thus I grab the reference to the inode.
> > Regards, > Peter Hurley > > PS - for the purpose of this discussion, /dev/pts/ptmx is equivalent.
-- []'s Herton
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