Re: [PATCH V2 1/3] seccomp: add generic code for jitted seccomp filters.

[Nicolas Schichan]

On 04/24/2013 01:43 AM, Andrew Morton wrote:
> On Mon, 22 Apr 2013 14:31:20 +0200 Nicolas Schichan <nschichan@xxxxxxxxxx> wrote:
> > Would including <uapi/linux/filter.h> instead of <linux/filter.h> in seccomp.h
> > be an acceptable solution ?
> >
> > I have tried that and (with an additional forward declaration of struct
> > sk_buff) an x86_64 "make clean; make allmodconfig" run finishes succesfully.
> >
> > If that's ok with you, I can resend the serie with that fix.
>
> It would be better to make the code and include tangle less complex,
> rather than more complex.
>
> Did we really need to move the `struct seccomp_filter' definition into
> the header file?  afaict that wasn't really necessary - we can add a
> few helper functions to kernel/seccomp.c and then have the remote code
> treat seccomp_filter in an opaque fashion rather than directly poking
> at its internals.

Hi,

I will resend a V3 of the patch serie with the accessors.

> btw, what on earth is going on with seccomp_jit_free()?  It does
> disturbing undocumented typecasting and it punts the module_free into a
> kernel thread for mysterious, undocumented and possibly buggy reasons.
>
> I realize it just copies bpf_jit_free().  The same observations apply there.

The reason for this hack for both seccomp filters and socket filters is that 
{seccomp,bpf}_jit_free are called from a softirq. module_free() cannot be 
called directly from softirq, as it will in turn call vfree() which will 
BUG_ON() if in_interrupt() is non zero. So to call module_free(), it is 
therefore required to be in a process context, which is provided by the work 
struct.

Here is the call stack for the socket filter case:

[<c0087bf8>] (vfree+0x28/0x2c) from [<c001fc5c>] (bpf_jit_free+0x10/0x18)
[<c001fc5c>] (bpf_jit_free+0x10/0x18) from 
[<c0231188>](sk_filter_release_rcu+0x10/0x1c)
[<c0231188>] (sk_filter_release_rcu+0x10/0x1c) from [<c0060bb4>] 
(__rcu_process_callbacks+0x98/0xac)
[<c0060bb4>] (__rcu_process_callbacks+0x98/0xac) from [<c0060bd8>] 
(rcu_process_callbacks+0x10/0x20)
[<c0060bd8>] (rcu_process_callbacks+0x10/0x20) from [<c0029498>] 
(__do_softirq+0xbc/0x194)
[<c0029498>] (__do_softirq+0xbc/0x194) from [<c00295b0>] (run_ksoftirqd+0x40/0x64)
[<c00295b0>] (run_ksoftirqd+0x40/0x64) from [<c0041954>] 
(smpboot_thread_fn+0x150/0x15c)
[<c0041954>] (smpboot_thread_fn+0x150/0x15c) from [<c003bb2c>] (kthread+0xa4/0xb0)
[<c003bb2c>] (kthread+0xa4/0xb0) from [<c0013450>] (ret_from_fork+0x14/0x24)

Here is the call stack for the seccomp filter case:

[<c0087c28>] (vfree+0x28/0x2c) from [<c0060834>] (put_seccomp_filter+0x6c/0x84)
[<c0060834>] (put_seccomp_filter+0x6c/0x84) from [<c0020db4>] 
(free_task+0x30/0x50)
[<c0020db4>] (free_task+0x30/0x50) from [<c0060be4>] 
(__rcu_process_callbacks+0x98/0xac)
[<c0060be4>] (__rcu_process_callbacks+0x98/0xac) from [<c0060c08>] 
(rcu_process_callbacks+0x10/0x20)
[<c0060c08>] (rcu_process_callbacks+0x10/0x20) from [<c00294c8>] 
(__do_softirq+0xbc/0x194)
[<c00294c8>] (__do_softirq+0xbc/0x194) from [<c00295e0>] (run_ksoftirqd+0x40/0x64)
[<c00295e0>] (run_ksoftirqd+0x40/0x64) from [<c0041984>] 
(smpboot_thread_fn+0x150/0x15c)
[<c0041984>] (smpboot_thread_fn+0x150/0x15c) from [<c003bb5c>] (kthread+0xa4/0xb0)
[<c003bb5c>] (kthread+0xa4/0xb0) from [<c0013450>] (ret_from_fork+0x14/0x24)

Regards,

--
Nicolas Schichan
Freebox SAS
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