Re: Linux-2.6.11 can't disable CAD

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Thu, 7 Apr 2005, Randy.Dunlap wrote:

On Thu, 7 Apr 2005 11:16:14 -0400 (EDT) Richard B. Johnson wrote:

|
| In the not-too distant past, one could disable Ctl-Alt-DEL.
| Can't do it anymore.

What should disabling C_A_D do?

| Script started on Thu 07 Apr 2005 10:58:11 AM EDT
| [SNIPPED leading stuff...]
|
| mprotect(0xb7fe4000, 28672, PROT_READ|PROT_EXEC) = 0
| brk(0)                                  = 0x804a000
| brk(0x8053000)                          = 0x8053000
| reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, LINUX_REBOOT_CMD_CAD_OFF)
= 0
| pause( <unfinished ...>
| _exit(0)                                = ?
| # exit
| Script done on Thu 07 Apr 2005 10:58:21 AM EDT


It's a program that executes the __NR_reboot syscall (88) after
putting the documented values into the appropriate registers.

What program is that?  I'm just echoing 0 | 1 into
/proc/sys/kernel/ctrl-alt-del , is that equivalent?
or have you tried that?


Doesn't matter. Many embedded systems don't have /proc because
they don't have any file-systems.

| Observe that reboot() returns 0 and `strace` understands what
| parameters were passed. The result is that, if I hit Ctl-Alt-Del,
| `init` will still execute the shutdown-order (INIT 0).

echo 0 > /proc/sys/kernel/ctrl-alt-del
 is same as CAD_OFF
echo 1
 is same as CAD_ON

I tested 2.4.28, 2.6.3, 2.6.9, 2.6.11, and all of them behaved
the same way for me.  If it's an issue with using a syscall
to change the setting, I'll be glad to look into that too.

observed behaviors:
CAD enabled + C_A_D keys => call machine_reboot()
 to reboot quickly, no normal shutdown sequence;
CAD disabled + C_A_D keys => kill init, go thru normal
 clean shutdown sequence;
are these the expected behaviors?

The expected behavior of the reported operation is for
Ctl-Alt-Del to no longer do anything. If the system-call
has been depreciated, then the call should return -1 and
errno should be ENOSYS. In such a case, I would have
to trap the key-sequence in some other way, not that
I know how without modifying the kernel.


| A side note, while researching this problem, I think I found
| that LINUX_REBOOT_MAGIC2 is Linus' birthday (in hex). Maybe
| the problem is that he no longer observes his birthday?

---
~Randy


Cheers,
Dick Johnson
Penguin : Linux version 2.6.11 on an i686 machine (5537.79 BogoMips).
 Notice : All mail here is now cached for review by Dictator Bush.
                 98.36% of all statistics are fiction.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux