Date: Sun, 22 Mar 2015 12:24:28 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Mateusz Guzik <mjguzik@gmail.com>, Tiwei Bie <btw@mail.ustc.edu.cn>, freebsd-hackers@freebsd.org Subject: Re: [PATCH] Finish the task 'Validate coredump format string' Message-ID: <20150322102428.GZ2379@kib.kiev.ua> In-Reply-To: <20150322101401.GH14650@dft-labs.eu> References: <1426946345-67889-1-git-send-email-btw@mail.ustc.edu.cn> <20150321200500.GC14650@dft-labs.eu> <20150322091853.GA89976@freebsd> <20150322101401.GH14650@dft-labs.eu>
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On Sun, Mar 22, 2015 at 11:14:01AM +0100, Mateusz Guzik wrote: > On Sun, Mar 22, 2015 at 05:19:40PM +0800, Tiwei Bie wrote: > > Sorry, I introduced a bug... allproc_lock could not be used to protect > > the access to corefilename[]. > > > > First off I committed the code, so the fault is on me. > > > Because, sysctl_kern_corefile() could be called very early: > > > [..] > > That is to say, when the tunable `kern.corefile' is set in loader.conf, > > sysctl_kern_corefile() will be called as the priority of (SI_SUB_KMEM, > > SI_ORDER_FIRST). > > > > At this time, allproc_lock is not initialized. > > > > I couldn't find a proper existing lock for this task. Maybe a dedicated > > lock needs to be created. And initialize it together with sysctlmemlock: > > > [..] > > Or maybe sysctlmemlock could be used, which is only acuqired when > > req.oldlen > PAGE_SIZE. > > > > > > I was somehow convinced that tunables are dealt with other code. > > If such sysctl handler is also called for tunables, the kernel should > pass a flag or some other indicator so that the function knows it is > dealing with a tunable and that would avoid locking and thus solve the > problem. > > I'm wondering if we should go a little bit further and get rid of > static char corefilename[MAXPATHLEN] > > and have a static char *corefilename instead. Accessing the array through the pointer dereference is micro-pessimization, as well as having to maintain metadata for the malloced memory, isn't it ? > > A dedicated sysinit func could fetch and validate the tunable, if any. > If no tunable was provided it would alloc memory for the default. Or you could move initialization of the sx in question earlier.
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