Date: Thu, 22 Apr 2010 17:51:06 -0700 From: Xin LI <delphij@delphij.net> To: Garrett Cooper <yanefbsd@gmail.com> Cc: FreeBSD-Hackers <freebsd-hackers@freebsd.org>, Matthew Fleming <matthew.fleming@isilon.com> Subject: Re: Error checking in ioctl(2)? Message-ID: <4BD0EEFA.90907@delphij.net> In-Reply-To: <u2o7d6fde3d1004221745o32173f04hdf77c080979026c8@mail.gmail.com> References: <w2v7d6fde3d1004221627jff97746bkcb8cd3ca5e5a7492@mail.gmail.com> <06D5F9F6F655AD4C92E28B662F7F853E039E33A7@seaxch09.desktop.isilon.com> <u2o7d6fde3d1004221745o32173f04hdf77c080979026c8@mail.gmail.com>
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On 2010/04/22 17:45, Garrett Cooper wrote:
> On Thu, Apr 22, 2010 at 4:36 PM, Matthew Fleming
> <matthew.fleming@isilon.com> wrote:
>>> Hi hackers,
>>> I realize that this isn't 100% userland code, so the checks should
>>> be minimalized, but when looking at the ioctl(2) syscall code (at
>>> least I think it is... there's another dupe hanging around in
>>> sys/dev/hptmv/ioctl.c), I had some questions related to the error
>>> handling not being done in the code:
>>>
>>> if (size > 0) {
>>> if (com & IOC_VOID) {
>>> /* Integer argument. */
>>> arg = (intptr_t)uap->data;
>>> data = (void *)&arg;
>>> size = 0;
>>> } else
>>> data = malloc((u_long)size, M_IOCTLOPS,
>>> M_WAITOK); /* XXX: can fail -- do we care? */
>>
>> malloc(9) with M_WAITOK cannot return NULL. So the rest of your XXX
>> comments are not at issue.
>>
>> Also, free(9) is documented to do the right thing when asked to
>> free(NULL).
>>
>> copyin/copyout are really just bcopy but unlike most kernel code they
>> are allowed to take a page fault. They deal with this by setting a
>> function pointer in PCB_ONFAULT, which is used in trap() to set a return
>> instruction pointer.
>
> Matt,
> Awesome. I can see I need to do a bit more reading in malloc(3) :)...
> Thanks for the info!
It's actually malloc(9)... I personally feels it pretty confusing at
the beginning when I learned about it.
Cheers,
- --
Xin LI <delphij@delphij.net> http://www.delphij.net/
FreeBSD - The Power to Serve! Live free or die
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