[Devel] Re: 2.6.20-lxc8: kernel panic with af_unix as module

[Pierre Peiffer]

Eric W. Biederman a écrit :
> 
>> In my case, when registering per_net__unix_root_table (in function
>> unix_sysctl_register in file net/unix/sysctl_net_unix.c), it tries to access the
>> child (which is per_net__unix_net_table) at the address 0x00000080 which is the
>> address of this symbol in the section .data.pernet of the module object, but not
>> a virtual address.
> 
> Hmm.  It should be a global offset in the .data.pernet section.

Yes, indeed, it is.

If I do some printk (in unix_sysctl_register) just before the panic, I get:

per_net(unix_root_table, net) = 0xf7e2dce0
per_net(unix_root_table, net)->child = 0x00000080    <= cause the panic

=> should be equal to this:

__per_net_base(unix_net_table)= 0xc03c7f40

And:
===================================================
$ objdump -D -j .data.pernet net/unix/unix.ko

net/unix/unix.ko:     file format elf32-i386

Disassembly of section .data.pernet:

00000000 <per_net__sysctl_unix_max_dgram_qlen>:
    0:   0a 00                   or     (%eax),%al
         ...

00000020 <per_net__unix_root_table>:
   20:   03 00                   add    (%eax),%eax
[...]

00000080 <per_net__unix_net_table>:
   80:   04 00                   add    $0x0,%al
   82:   00 00                   add    %al,(%eax)
...
===================================================

The init of per_net(unix_root_table, net)->child is done with the offset of 
__per_net_base(unix_net_table) in the module, and never translated to its 
virtual address.

It looks like the module loader translates/relocates correctly the address of 
__per_net_base(unix_net_table), but the not the address (value of) 
per_net(unix_root_table, net)->child ???

But if I do:
$ objdump -r -j .data.pernet net/unix/unix.ko

net/unix/unix.ko:     file format elf32-i386

RELOCATION RECORDS FOR [.data.pernet]:
OFFSET   TYPE              VALUE
00000024 R_386_32          .rodata.str1.1
00000034 R_386_32          .data.pernet  <== per_net__unix_root_table->child (*)
00000070 R_386_32          .data.pernet
00000084 R_386_32          .rodata.str1.1
00000094 R_386_32          .data.pernet  <== per_net__unix_net_table>->child (?)
000000e4 R_386_32          .rodata.str1.1
000000e8 R_386_32          per_net__sysctl_unix_max_dgram_qlen
000000f8 R_386_32          proc_dointvec

(*) If I well read/understand, this relocation entry should correspond to 
per_net__unix_root_table->child and should be translated at load time, but it 
isn't ?


> 
> Thanks.  I will go back and look but I don't plan on back porting
> anything for 2.6.20.  I'm lazy and do not have enough hours in the
> day. :)

No problem.
Thanks.

-- 
Pierre
_______________________________________________
Containers mailing list
Containers at lists.linux-foundation.org
https://lists.linux-foundation.org/mailman/listinfo/containers