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
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