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Debian 8 system is not fully functional

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  Debian 8 system is not fully functional zhang yang <shuyang9708@gmail.com> - 2020-12-23 15:40 +0100
    Re: Debian 8 system is not fully functional Dan Ritter <dsr@randomstring.org> - 2020-12-23 16:00 +0100
      Re: Debian 8 system is not fully functional zhang yang <shuyang9708@gmail.com> - 2020-12-24 06:10 +0100
        Re: Debian 8 system is not fully functional Greg Wooledge <wooledg@eeg.ccf.org> - 2020-12-24 14:10 +0100
          Re: Debian 8 system is not fully functional Kenneth Parker <sea7kenp@gmail.com> - 2020-12-24 15:40 +0100

#229938 — Debian 8 system is not fully functional

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When I write a raw socket to send packets in Linux C, it shows:
WARNNING:The current server does not support IP spoofing.
How to set up debian8 system to use this function

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#229940

zhang yang wrote: 
> When I write a raw socket to send packets in Linux C, it shows:
> WARNNING:The current server does not support IP spoofing.
> How to set up debian8 system to use this function

1. Read
https://www.kernel.org/doc/html/latest/networking/ip-sysctl.html

2. Install a Debian 10 (stable) system. Debian supports
upgrading in place to 9, then 10. If you're doing spoofing, you 
are security-conscious; if you are security-conscious, you
should be running stable, not old-old-stable.

3. Alternatively, you don't mean to be spoofing and your problem
is in your code.

-dsr-

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#229960

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When I turn it on
https://www.kernel.org/doc/html/latest/networking/ip-sysctl.html I guess
it's IP_ Dynaddr - Boolean.
If set non-zero, enables support for dynamic addresses. If set to a
non-zero value larger than 1, a kernel log message will be printed when
dynamic address rewriting occurs.Default : 0.
Should it be set to 1 to send packets disguised as IP? But when I use vi
IP_ dynaddr
To modify and save the prompt: "IP"_ dynaddr" E212: Can't open file for
writing“.
So I used Chmod 777 ip_ dynaddr authority, display error: Chmod: changing
permissions of 'IP_ dynaddr': Operation not permitted.
I use chaddr - i ip_dynaddr command to removes attributes and displays an
error: chattr: Inappropriate ioctl for device while reading flags on
ip_dynaddr.  How to set dynaddr?



On Wed, Dec 23, 2020 at 10:51 PM Dan Ritter <dsr@randomstring.org> wrote:

> zhang yang wrote:
> > When I write a raw socket to send packets in Linux C, it shows:
> > WARNNING:The current server does not support IP spoofing.
> > How to set up debian8 system to use this function
>
> 1. Read
> https://www.kernel.org/doc/html/latest/networking/ip-sysctl.html
>
> 2. Install a Debian 10 (stable) system. Debian supports
> upgrading in place to 9, then 10. If you're doing spoofing, you
> are security-conscious; if you are security-conscious, you
> should be running stable, not old-old-stable.
>
> 3. Alternatively, you don't mean to be spoofing and your problem
> is in your code.
>
> -dsr-
>

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#229965

On Thu, Dec 24, 2020 at 12:49:30PM +0800, zhang yang wrote:
> IP_ dynaddr
> To modify and save the prompt: "IP"_ dynaddr" E212: Can't open file for
> writing“.
> So I used Chmod 777 ip_ dynaddr authority, display error: Chmod: changing
> permissions of 'IP_ dynaddr': Operation not permitted.
> I use chaddr - i ip_dynaddr command to removes attributes and displays an
> error: chattr: Inappropriate ioctl for device while reading flags on
> ip_dynaddr.  How to set dynaddr?

For the benefit of others, the file in question is

/proc/sys/net/ipv4/ip_dynaddr

/proc is not a regular file system.  It's an interface to pieces of the
kernel.  Some of these pieces can be read by everyone.  Almost none of
them can be *written* by everyone -- you usually have to be root to
write to them.

chmod 777 is almost always a *huge* mistake.  If the permissions on a
file are stopping you from doing someting, there's usually a reason
for that.  Destroying the permissions on the file is not the right answer.
Elevating yourself to a higher power level is.

Now, the next thing you'll want to know is that while root can probably
write to this file, it can't necessary *edit* the file with a text
editor.  You're expected to use a much lower level of access to open
the file, write to it, and close it.  Typically that's done with

echo something > /proc/whatever

Of course this redirection means that it's your shell who needs
privileges to open the file for writing.  If you try it as your
regular user, you'll encounter the "permission denied" error that
you already saw.

The expected course of action is for you to do it from a root shell,
which you obtain by using su or sudo.

$ su
Password: 
# echo something > /proc/whatever
# exit
$ 

If you're not a fan of su, or if you're one of those people who has
decided not to have a root password (a bad idea!), then you can get
a root shell with sudo -s:

$ sudo -s
# echo something >/proc/whatever
# exit
$ 

(sudo may prompt you for your password if you haven't used sudo in that
terminal in the last few minutes.)

Some people will try to be clever and do this:

sudo echo something > /proc/whatever

That will not work, for the reasons explained at
<https://mywiki.wooledge.org/BashPitfalls#pf53>.  You may use one of
the quoted forms on that page if you prefer.  But the original design
of the files in /proc was for users with a root shell to perform shell
redirections.  Not for sudo.

Also, while I'm here talking about su, bear in mind that Debian decided
to become more like Red Hat and replaced their version of su with the
one used by Red Hat, and didn't bother configuring it to maintain backward
compatibility with the previous version.  See
<https://wiki.debian.org/NewInBuster#Changes> for workarounds, including
how to configure su to behave sanely.

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#229966

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On Thu, Dec 24, 2020, 8:08 AM Greg Wooledge <wooledg@eeg.ccf.org> wrote:

> On Thu, Dec 24, 2020 at 12:49:30PM +0800, zhang yang wrote:
> > IP_ dynaddr
> > To modify and save the prompt: "IP"_ dynaddr" E212: Can't open file for
> > writing“.
> > So I used Chmod 777 ip_ dynaddr authority, display error: Chmod: changing
> > permissions of 'IP_ dynaddr': Operation not permitted.
> > I use chaddr - i ip_dynaddr command to removes attributes and displays an
> > error: chattr: Inappropriate ioctl for device while reading flags on
> > ip_dynaddr.  How to set dynaddr?
>
> For the benefit of others, the file in question is
>
> /proc/sys/net/ipv4/ip_dynaddr
>
> /proc is not a regular file system.  It's an interface to pieces of the
> kernel.  Some of these pieces can be read by everyone.  Almost none of
> them can be *written* by everyone -- you usually have to be root to
> write to them.
>
> chmod 777 is almost always a *huge* mistake.  If the permissions on a
> file are stopping you from doing someting, there's usually a reason
> for that.  Destroying the permissions on the file is not the right answer.
> Elevating yourself to a higher power level is.
>
> Now, the next thing you'll want to know is that while root can probably
> write to this file, it can't necessary *edit* the file with a text
> editor.  You're expected to use a much lower level of access to open
> the file, write to it, and close it.  Typically that's done with
>
> echo something > /proc/whatever
>
> Of course this redirection means that it's your shell who needs
> privileges to open the file for writing.  If you try it as your
> regular user, you'll encounter the "permission denied" error that
> you already saw.
>
> The expected course of action is for you to do it from a root shell,
> which you obtain by using su or sudo.
>
> $ su
> Password:
> # echo something > /proc/whatever
> # exit
> $
>
> If you're not a fan of su, or if you're one of those people who has
> decided not to have a root password (a bad idea!), then you can get
> a root shell with sudo -s:
>
> $ sudo -s
> # echo something >/proc/whatever
> # exit
> $
>
> (sudo may prompt you for your password if you haven't used sudo in that
> terminal in the last few minutes.)
>
> Some people will try to be clever and do this:
>
> sudo echo something > /proc/whatever
>
> That will not work, for the reasons explained at
> <https://mywiki.wooledge.org/BashPitfalls#pf53>.


+10

That is an Awesome page you have there, Greg!  I have Bookmarked it.

>

You may use one of
> the quoted forms on that page if you prefer.  But the original design
> of the files in /proc was for users with a root shell to perform shell
> redirections.  Not for sudo.
>
> Also, while I'm here talking about su, bear in mind that Debian decided
> to become more like Red Hat and replaced their version of su with the
> one used by Red Hat, and didn't bother configuring it to maintain backward
> compatibility with the previous version.  See
> <https://wiki.debian.org/NewInBuster#Changes> for workarounds...
>

Also good.  I was never affected by the change, because I always use "su
-".

Kenneth Parker

>

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