Re: [PATCH v4 2/4] seccomp: Add sysctl to configure actions that should be logged

[Tyler Hicks <tyhicks@canonical.com>]

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On 02/15/2017 07:10 PM, Kees Cook wrote:
> On Mon, Feb 13, 2017 at 7:55 PM, Tyler Hicks <tyhicks@canonical.com> wrote:
>> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
>> index e36dfe9..270a227 100644
>> --- a/kernel/seccomp.c
>> +++ b/kernel/seccomp.c
>> @@ -509,6 +509,22 @@ static void seccomp_send_sigsys(int syscall, int reason)
>>  }
>>  #endif /* CONFIG_SECCOMP_FILTER */
>>
>> +static u32 seccomp_log_max_action = SECCOMP_RET_KILL;
>> +
>> +static inline void seccomp_log(unsigned long syscall, long signr, u32 action)
>> +{
>> +       /* Force an audit message to be emitted when the action is not greater
>> +        * than the configured maximum action.
>> +        */
>> +       if (action <= seccomp_log_max_action)
>> +               return __audit_seccomp(syscall, signr, action);
>> +
>> +       /* Let the audit subsystem decide if the action should be audited based
>> +        * on whether the current task itself is being audited.
>> +        */
> 
> Nitpick on comment style, please use:
> 
> /*
>  * line 1
>  * line 2...
>  */

No problem.

> 
>> +       return audit_seccomp(syscall, signr, action);
>> +}
>> +
>>  /*
>>   * Secure computing mode 1 allows only read/write/exit/sigreturn.
>>   * To be fully secure this must be combined with rlimit
>> @@ -534,7 +550,7 @@ static void __secure_computing_strict(int this_syscall)
>>  #ifdef SECCOMP_DEBUG
>>         dump_stack();
>>  #endif
>> -       audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL);
>> +       seccomp_log(this_syscall, SIGKILL, SECCOMP_RET_KILL);
>>         do_exit(SIGKILL);
>>  }
>>
>> @@ -633,18 +649,30 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
>>                 return 0;
>>
>>         case SECCOMP_RET_ALLOW:
>> +               /* Open-coded seccomp_log(), optimized for the RET_ALLOW hot
>> +                * path.
>> +                *
>> +                * We only want to log RET_ALLOW actions when the admin has
>> +                * configured them to be logged via the log_max_action sysctl.
>> +                * Therefore, call __audit_seccomp() directly so that RET_ALLOW
>> +                * actions are not audited simply because the task is being
>> +                * audited.
>> +                */
>> +               if (unlikely(seccomp_log_max_action == SECCOMP_RET_ALLOW))
>> +                       __audit_seccomp(this_syscall, 0, action);
>> +
>>                 return 0;
>>
>>         case SECCOMP_RET_KILL:
>>         default:
>> -               audit_seccomp(this_syscall, SIGSYS, action);
>> +               seccomp_log(this_syscall, SIGSYS, action);
>>                 do_exit(SIGSYS);
>>         }
>>
>>         unreachable();
>>
>>  skip:
>> -       audit_seccomp(this_syscall, 0, action);
>> +       seccomp_log(this_syscall, 0, action);
>>         return -1;
>>  }
>>  #else
>> @@ -917,12 +945,96 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
>>  #define SECCOMP_RET_TRACE_NAME         "trace"
>>  #define SECCOMP_RET_ALLOW_NAME         "allow"
>>
>> +/* Largest strlen() of all action names */
>> +#define SECCOMP_RET_MAX_NAME_LEN       5
>> +
>>  static char seccomp_actions_avail[] = SECCOMP_RET_KILL_NAME    " "
>>                                       SECCOMP_RET_TRAP_NAME     " "
>>                                       SECCOMP_RET_ERRNO_NAME    " "
>>                                       SECCOMP_RET_TRACE_NAME    " "
>>                                       SECCOMP_RET_ALLOW_NAME;
>>
>> +struct seccomp_action_name {
>> +       u32             action;
>> +       const char      *name;
>> +};
>> +
>> +static struct seccomp_action_name seccomp_action_names[] = {
> 
> As long as I'm nit-picking, this can be const too. :)

I'll have to cast to a non-const pointer when assigning ctl_table.data
but I think that's fine in this case.

Tyler

> 
> -Kees
> 



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