netdev - Re: Linux 2.6.38-rc4 (hysdn: BUG)

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Date:	Wed, 9 Feb 2011 11:44:00 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Karsten Keil <isdn@...ux-pingi.de>
Subject: Re: Linux 2.6.38-rc4 (hysdn: BUG)

On Wed, Feb 9, 2011 at 9:24 AM, Randy Dunlap <randy.dunlap@...cle.com> wrote:
>
> on x86_64.  no HYSDN hardware found (correct).
> Nearly allmodconfig.
>
>
> [   65.397577] HYSDN: module Rev: 1.6.6.6 loaded
> [   65.397584] HYSDN: network interface Rev: 1.8.6.4
> [   65.398057] HYSDN: 0 card(s) found.
> [   65.398121] BUG: unable to handle kernel paging request at ffffffffa06c99f0
> [   65.398269] IP: [<ffffffffa06c68ba>] hysdn_getrev+0x2e/0x50 [hysdn]
> [   65.398379] PGD 1a14067 PUD 1a18063 PMD 6f6c1067 PTE 800000006ce8c161
> [   65.398613] Oops: 0003 [#1] SMP DEBUG_PAGEALLOC
> [   65.400030]
> [   65.400030] Pid: 2497, comm: modprobe Not tainted 2.6.38-rc4 #1 0TY565/OptiPlex 745
> [   65.400030] RIP: 0010:[<ffffffffa06c68ba>]  [<ffffffffa06c68ba>] hysdn_getrev+0x2e/0x50 [hysdn]
> [   65.400030] RSP: 0018:ffff88006eec1e68  EFLAGS: 00010206
> [   65.400030] RAX: ffffffffa06c99f1 RBX: ffffffffa06c99e9 RCX: ffff88007c4159a0

The instruction sequence decodes to

  1e:	be 24 00 00 00       	mov    $0x24,%esi
  23:	48 89 df             	mov    %rbx,%rdi
  26:	e8 5b 39 c0 e0       	callq  0xffffffffe0c03986
  2b:*	c6 40 ff 00          	movb   $0x0,-0x1(%rax)     <-- trapping instruction

which seems to be this

                p = strchr(rev, '$');
                *--p = 0;

code. And yes, it's total crap, because while "p" and "rev" are "char
*", the string that is passed in is actually of type "const char *",
so that function is seriously broken. It's also seriously broken to
not test that "p" is non-NULL - the function would just break if there
is a colon in the string but not a '$'.

And hysdn_procconf_init() passes in a constant string to the thing:

    static char *hysdn_procconf_revision = "$Revision: 1.8.6.4 $";

What happens is that it breaks when we mark the constant section as
read-only, because you have CONFIG_DEBUG_RODATA enabled.

So the fix seems to be to
 - fix the prototype for hysdn_getrev() to not have "const".
 - fix hysdn_procconf_init() to not pass in a constant string to it

The minimal patch would appear to be something like the appended. UNTESTED!

Btw, all of this code seems to go back to before the git history even
started, so it doesn't seem to be new. I assume you haven't tried
booting these all-module kernels before? Or is it just the
DEBUG_RODATA thing that is new for you?

                    Linus

View attachment "patch.diff" of type "text/x-patch" (1685 bytes)