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SubjectRe: [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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