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Date: Sat, 15 Feb 2014 18:09:46 -0800 (PST)
From: John <da_audiophile@...oo.com>
To: Borislav Petkov <bp@...en8.de>
Cc: lkml <linux-kernel@...r.kernel.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"stephen@...workplumber.org" <stephen@...workplumber.org>,
"mlindner@...vell.com" <mlindner@...vell.com>,
Trond Myklebust <trond.myklebust@...marydata.com>,
"J. Bruce Fields" <bfields@...ldses.org>
Subject: Re: [BUG] unable to handle kernel NULL pointer dereference
----- Original Message -----
> From: Borislav Petkov <>
> Sent: Saturday, February 15, 2014 6:25 PM
> Subject: Re: [BUG] unable to handle kernel NULL pointer dereference
>
> On Sat, Feb 15, 2014 at 01:04:22PM -0800, John wrote:
>> Thanks for the reply, Boris. The .config is unmodified
>> from the Arch Distro default for 3.13.3-1 which can be found
>> here: http://pastebin.com/LPGZ8ZqA
>
> Yep, it is that struct net *net argument to put_pipe_version() which is NULL:
>
> 12: 55 push %ebp
> 13: 89 e5 mov %esp,%ebp
> 15: 56 push %esi
> 16: 53 push %ebx
> 17: 3e 8d 74 26 00 lea %ds:0x0(%esi,%eiz,1),%esi
> 1c: 8b 1d 28 e9 a3 f8 mov 0xf8a3e928,%ebx
> 22: 89 c6 mov %eax,%esi
> 24: e8 59 64 5f c8 call 0xc85f6482
> 29: 85 db test %ebx,%ebx
> 2b:* 8b 86 58 08 00 00 mov 0x858(%esi),%eax <-- trapping
> instruction
>
> put_pipe_version:
> pushl %ebp #
> movl %esp, %ebp #,
> pushl %esi #
> pushl %ebx #
> call mcount
> movl sunrpc_net_id, %ebx # sunrpc_net_id, sunrpc_net_id.130
> movl %eax, %esi # net, net
> call __rcu_read_lock #
> testl %ebx, %ebx # sunrpc_net_id.130
> movl 2136(%esi), %eax # MEM[(struct net_generic * const *)net_4(D) +
> 2136B], ng <-- trapping insn
>
>
> [ 137.689996] ESI: 00000000 EDI: f56efc00 EBP: f568fee8 ESP: f568fee0
> ^^^^^^^^
>
> Here's the c/asm interleaved version:
>
> static void put_pipe_version(struct net *net)
> {
> d80: 55 push %ebp
> d81: 89 e5 mov %esp,%ebp
> d83: 56 push %esi
> d84: 53 push %ebx
> d85: e8 fc ff ff ff call d86 <put_pipe_version+0x6>
> d86: R_386_PC32 mcount
> struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
> d8a: 8b 1d 00 00 00 00 mov 0x0,%ebx
> d8c: R_386_32 sunrpc_net_id
> spin_unlock(&pipe_version_lock);
> return ret;
> }
>
> static void put_pipe_version(struct net *net)
> {
> d90: 89 c6 mov %eax,%esi
> * block, but only when acquiring spinlocks that are subject to priority
> * inheritance.
> */
> static inline void rcu_read_lock(void)
> {
> __rcu_read_lock();
> d92: e8 fc ff ff ff call d93 <put_pipe_version+0x13>
> d93: R_386_PC32 __rcu_read_lock
> struct net_generic *ng;
> void *ptr;
>
> rcu_read_lock();
> ng = rcu_dereference(net->gen);
> BUG_ON(id == 0 || id > ng->len);
> d97: 85 db test %ebx,%ebx
> {
> struct net_generic *ng;
> void *ptr;
>
> rcu_read_lock();
> ng = rcu_dereference(net->gen);
> d99: 8b 86 58 08 00 00 mov 0x858(%esi),%eax
> <-- trapping insn
>
>
> I guess you could avoid the crash if you did
>
> if (!net)
> return;
>
> in put_pipe_version() but this hardly is the right solution. Someone
> else has to make sense of this thing, not me. :-)
>
> HTH.
I copy someone you cc'ed on this understands it. I have no idea what you wrote :)
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