Re: 3.15: kernel BUG at kernel/auditsc.c:1525!

From: Toralf FÃrster
Date: Mon Jun 16 2014 - 14:36:45 EST

On 06/16/2014 08:24 PM, Andy Lutomirski wrote:
> On Mon, Jun 16, 2014 at 11:21 AM, Toralf FÃrster <toralf.foerster@xxxxxx> wrote:
>> On 06/16/2014 08:15 PM, Andy Lutomirski wrote:
>>> On Mon, Jun 16, 2014 at 10:59 AM, Toralf FÃrster <toralf.foerster@xxxxxx> wrote:
>>>> On 06/16/2014 07:50 PM, Andy Lutomirski wrote:
>>>>> cc: eparis. This might be a new audit bug.
>>>>>
>>>>> On Mon, Jun 16, 2014 at 10:36 AM, Toralf FÃrster <toralf.foerster@xxxxxx> wrote:
>>>>>> On 06/16/2014 07:32 PM, Andy Lutomirski wrote:
>>>>>>> On Mon, Jun 16, 2014 at 10:29 AM, Richard Weinberger <richard@xxxxxx> wrote:
>>>>>>>> Am 16.06.2014 19:25, schrieb Andy Lutomirski:
>>>>>>>>> On Mon, Jun 16, 2014 at 10:21 AM, Richard Weinberger
>>>>>>>>> <richard.weinberger@xxxxxxxxx> wrote:
>>>>>>>>>> On Mon, Jun 16, 2014 at 6:33 PM, Toralf FÃrster <toralf.foerster@xxxxxx> wrote:
>>>>>>>>>>> $ cat syscall.c
>>>>>>>>>>> #include <unistd.h>
>>>>>>>>>>> #include <sys/syscall.h>
>>>>>>>>>>> int main(){return syscall(1000)!=-1;}
>>>>>>>>>
>>>>>>>>> What architecture are you building for? On i386 and x86_64, 1000
>>>>>>>>> shouldn't be big enough to trigger this.
>>>>>>>>
>>>>>>>> Toralf, is this an UML kernel?
>>>>>>>>
>>>>>>>
>>>>>>> I'm also interested in the userspace architecture. If it's x32
>>>>>>> userspace, then I'm not surprised that there's a problem.
>>>>>>
>>>>>> It is a x86 system (ThinkPad T420) - not x32.
>>>>>
>>>>> I don't think this is CVE-2014-3917. It looks like you're hitting this BUG:
>>>>>
>>>>> BUG_ON(context->in_syscall || context->name_count);
>>>>>
>>>>> Can you send the output of:
>>>>>
>>>>> auditctl -l [run as root]
>>>>>
>>>>> and
>>>>>
>>>>> dmesg |grep audit
>>>>>
>>>>> Are you using ptrace or anything like that (e.g. strace) when you
>>>>> trigger this? Are you using a funny glibc version? Do you have
>>>>> selinux or something like that enabled?
>>>>>
>>>>> --Andy
>>>>>
>>>> n22 ~ # auditctl -l
>>>> LIST_RULES: exit,never arch=1073741827 (0x40000003) syscall=read,write,open,close,brk,fcntl,dup2,mmap,munmap,stat,fstat,nanosleep,rt_sigaction
>>>>
>>>>
>>>> no ptrace/strace/SELinux, this is a stable x86 Gentoo Linux, glibc is 2.17, unstable are just KDE + Co.
>>>>
>>>> (@Richard: no. it is not an UML guest, I just stumbled over this while I tried to upgrade an unstable ~x86 Gentoo UML image using chroot)
>>>>
>>>> The trigger is just given by that C one-liner and kernel 3.15 (erm, I did not checked, if 3.14.x hit its too)
>>>
>>> At the very least, it looks like sysret_audit can result in invoking
>>> the audit exit hook twice. That's not what's causing this, but it
>>> still looks fishy.
>>>
>>> Toralf, can you run your test program under strace, post the output,
>>> and see whether it still crashes? There's some chance that strace
>>> will "fix" it, since strace causes a different set of hooks to run.
>>>
>> tfoerste@n22 ~/tmp $ cat syscall.c
>> #include <unistd.h>
>> #include <sys/syscall.h>
>> int main(){return syscall(1000)!=-1;}
>>
>> tfoerste@n22 ~/tmp $ gcc strcmp.c && strace ./a.out
>> execve("./a.out", ["./a.out"], [/* 75 vars */]) = 0
>> brk(0) = 0x85f3000
>> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7750000
>> access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
>> open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
>> fstat64(3, {st_mode=S_IFREG|0644, st_size=164108, ...}) = 0
>> mmap2(NULL, 164108, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7727000
>> close(3) = 0
>> open("/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
>> read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0 \316\1\0004\0\0\0"..., 512) = 512
>> fstat64(3, {st_mode=S_IFREG|0755, st_size=1750448, ...}) = 0
>> mmap2(NULL, 1759980, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7579000
>> mmap2(0xb7721000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1a8000) = 0xb7721000
>> mmap2(0xb7724000, 10988, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb7724000
>> close(3) = 0
>> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7578000
>> set_thread_area({entry_number:-1 -> 6, base_addr:0xb75786c0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
>> mprotect(0xb7721000, 8192, PROT_READ) = 0
>> mprotect(0x8049000, 4096, PROT_READ) = 0
>> mprotect(0xb7774000, 4096, PROT_READ) = 0
>> munmap(0xb7727000, 164108) = 0
>> fstat64(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(136, 5), ...}) = 0
>> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb774f000
>> write(1, "1\n", 21
>> ) = 2
>
> Does this mean it didn't OOPS? And where's the write(1, "1\n", 2)
> coming from? Are you sure you straced the right thing?
>
> --Andy
>

Ick - sry ,

here is the trace of the syscall.c, but as you expected, no BUG in syslog if I use strace :

tfoerste@n22 ~/tmp $ gcc syscall.c && strace ./a.out
execve("./a.out", ["./a.out"], [/* 75 vars */]) = 0
brk(0) = 0x8d75000
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb76ee000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=164108, ...}) = 0
mmap2(NULL, 164108, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb76c5000
close(3) = 0
open("/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0 \316\1\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1750448, ...}) = 0
mmap2(NULL, 1759980, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7517000
mmap2(0xb76bf000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1a8000) = 0xb76bf000
mmap2(0xb76c2000, 10988, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb76c2000
close(3) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7516000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb75166c0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
mprotect(0xb76bf000, 8192, PROT_READ) = 0
mprotect(0x8049000, 4096, PROT_READ) = 0
mprotect(0xb7712000, 4096, PROT_READ) = 0
munmap(0xb76c5000, 164108) = 0
syscall_1000(0, 0x8048469, 0xb76c1000, 0x8048460, 0, 0) = -1 (errno 38)
exit_group(0) = ?
+++ exited with 0 +++

--
Toralf

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