Date: Thu, 29 Apr 2010 23:23:28 +0200 (CEST) From: "=?ISO-8859-15?Q?Luk=E1=A8_Czerner?=" <czerner.lukas@gmail.com> To: Ryan Stone <rysto32@gmail.com> Cc: freebsd-hackers@freebsd.org, =?ISO-8859-15?Q?Luk=E1=A8_Czerner?= <czerner.lukas@gmail.com> Subject: Re: ioctl, copy string from user Message-ID: <alpine.DEB.1.10.1004292320540.30007@a04-0215a.kn.vutbr.cz> In-Reply-To: <x2sbc2d971004291419o546d8895vd4fcab2ee15f37b9@mail.gmail.com> References: <alpine.DEB.1.10.1004291938210.30007@a04-0215a.kn.vutbr.cz> <201004291418.09768.jhb@freebsd.org> <alpine.DEB.1.10.1004292114360.30007@a04-0215a.kn.vutbr.cz> <201004291606.35899.jhb@freebsd.org> <alpine.DEB.1.10.1004292220170.30007@a04-0215a.kn.vutbr.cz> <alpine.DEB.1.10.1004292256580.30007@a04-0215a.kn.vutbr.cz> <x2sbc2d971004291419o546d8895vd4fcab2ee15f37b9@mail.gmail.com>
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On Thu, 29 Apr 2010, Ryan Stone wrote:
> Date: Thu, 29 Apr 2010 17:19:41 -0400
> From: Ryan Stone <rysto32@gmail.com>
> To: LukᨠCzerner <czerner.lukas@gmail.com>
> Cc: freebsd-hackers@freebsd.org
> Subject: Re: ioctl, copy string from user
>
> > Apparently I need to tell ioctl how big is the variable I am
> > providing to it ([MAXLEN]). The odd thing is, when I have a structure
> > like this:
> >
> > struct lrfs_attach_info {
> > char *name;
> > int priority;
> > };
> >
> > and I pass the pointer to that structure to the ioctl, it just
> > works. I can even use the 'name' string from the structure without
> > any problems, apparently it translates the pointer properly, but I
> > did not expect this...
>
> I think that you'll find that what actually happens is that you're
> reading from the userspace pointer. That will work as long as the
> pointer is mapped, but you'll panic if what it points to gets swapped
> out or is invalid.
>
Hmmm, I can prevent the pointer to be invalidated, but I doubt I can
prevent to the pointer to been swapped out. Is there some better way
? Allocate it statically (char name[MAXLEN]), then it gets copied
as whole to the kernel space, isn't it ?
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