Re: [Qemu-devel] [PATCH 3/4] Support for "double whitelist" filters

[Corey Bryant <coreyb@linux.vnet.ibm.com>]

On 10/19/2012 01:04 PM, Blue Swirl wrote:
> On Wed, Oct 17, 2012 at 1:15 PM, Eduardo Otubo <otubo@linux.vnet.ibm.com> wrote:
>> This patch includes a second whitelist right before the main loop. It's
>> a smaller and more restricted whitelist, excluding execve() among many
>> others.
>>
>> Signed-off-by: Eduardo Otubo <otubo@linux.vnet.ibm.com>
>> ---
>>   qemu-seccomp.c | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++++------
>>   qemu-seccomp.h |  7 ++++-
>>   vl.c           | 13 +++++++-
>>   3 files changed, 103 insertions(+), 11 deletions(-)
>>
>> diff --git a/qemu-seccomp.c b/qemu-seccomp.c
>> index a25f2fa..9c68af5 100644
>> --- a/qemu-seccomp.c
>> +++ b/qemu-seccomp.c
>> @@ -13,6 +13,7 @@
>>    * GNU GPL, version 2 or (at your option) any later version.
>>    */
>>   #include <stdio.h>
>> +#include <stdlib.h>
>>   #include <seccomp.h>
>>   #include "qemu-seccomp.h"
>>
>> @@ -21,7 +22,7 @@ struct QemuSeccompSyscall {
>>       uint8_t priority;
>>   };
>>
>> -static const struct QemuSeccompSyscall seccomp_whitelist[] = {
>> +static const struct QemuSeccompSyscall seccomp_whitelist_init[] = {
>>       { SCMP_SYS(timer_settime), 255 },
>>       { SCMP_SYS(timer_gettime), 254 },
>>       { SCMP_SYS(futex), 253 },
>> @@ -118,27 +119,102 @@ static const struct QemuSeccompSyscall seccomp_whitelist[] = {
>>       { SCMP_SYS(accept4), 242 }
>>   };
>>
>> -int seccomp_start(void)
>> +static const struct QemuSeccompSyscall seccomp_whitelist_main_loop[] = {
>> +    { SCMP_SYS(timer_settime), 255 },
>> +    { SCMP_SYS(timer_gettime), 254 },
>> +    { SCMP_SYS(futex), 253 },
>> +    { SCMP_SYS(select), 252 },
>> +    { SCMP_SYS(recvfrom), 251 },
>> +    { SCMP_SYS(sendto), 250 },
>> +    { SCMP_SYS(read), 249 },
>> +    { SCMP_SYS(brk), 248 },
>> +    { SCMP_SYS(mmap), 247 },
>> +#if defined(__i386__)
>> +    { SCMP_SYS(fcntl64), 245 },
>> +    { SCMP_SYS(fstat64), 245 },
>> +    { SCMP_SYS(stat64), 245 },
>> +    { SCMP_SYS(getgid32), 245 },
>> +    { SCMP_SYS(getegid32), 245 },
>> +    { SCMP_SYS(getuid32), 245 },
>> +    { SCMP_SYS(geteuid32), 245 },
>> +    { SCMP_SYS(sigreturn), 245 },
>> +    { SCMP_SYS(_newselect), 245 },
>> +    { SCMP_SYS(_llseek), 245 },
>> +    { SCMP_SYS(mmap2), 245},
>> +    { SCMP_SYS(sigprocmask), 245 },
>> +#endif
>> +    { SCMP_SYS(exit), 245 },
>> +    { SCMP_SYS(timer_delete), 245 },
>> +    { SCMP_SYS(exit_group), 245 },
>> +    { SCMP_SYS(rt_sigreturn), 245 },
>> +    { SCMP_SYS(madvise), 245 },
>> +    { SCMP_SYS(write), 244 },
>> +    { SCMP_SYS(fcntl), 243 },
>> +    { SCMP_SYS(tgkill), 242 },
>> +    { SCMP_SYS(rt_sigaction), 242 },
>> +    { SCMP_SYS(pipe2), 242 },
>> +    { SCMP_SYS(munmap), 242 },
>> +    { SCMP_SYS(mremap), 242 },
>> +    { SCMP_SYS(getsockname), 242 },
>> +    { SCMP_SYS(getpeername), 242 },
>> +    { SCMP_SYS(close), 242 },
>> +    { SCMP_SYS(accept4), 242 }
>
> It's nice to see that for example open, creat, unlink, socket, bind,
> mprotect, setrlimit and kill are not present.
>

Hmm, well open minimally needs to be added to this list so that drives 
can be hotplugged.

>> +};
>> +
>> +static int
>> +process_whitelist(const struct QemuSeccompSyscall *whitelist,
>> +                  unsigned int size, scmp_filter_ctx *ctx)
>>   {
>>       int rc = 0;
>> +
>>       unsigned int i = 0;
>> -    scmp_filter_ctx ctx;
>> +
>> +    for (i = 0; i < size; i++) {
>> +        rc = seccomp_rule_add(ctx, SCMP_ACT_ALLOW, whitelist[i].num, 0);
>> +        if (rc < 0) {
>> +            return -1;
>> +        }
>> +
>> +        rc = seccomp_syscall_priority(ctx, whitelist[i].num,
>> +                                      whitelist[i].priority);
>> +        if (rc < 0) {
>> +            return -1;
>> +        }
>> +    }
>> +    return 0;
>> +}
>> +
>> +int
>> +seccomp_start(enum whitelist_mode mode, scmp_filter_ctx *ctx)
>> +{
>> +    int rc = 0;
>>
>>       ctx = seccomp_init(SCMP_ACT_KILL);
>>       if (ctx == NULL) {
>> +        rc = -1;
>>           goto seccomp_return;
>>       }
>>
>> -    for (i = 0; i < ARRAY_SIZE(seccomp_whitelist); i++) {
>> -        rc = seccomp_rule_add(ctx, SCMP_ACT_ALLOW, seccomp_whitelist[i].num, 0);
>> -        if (rc < 0) {
>> +    switch (mode) {
>> +    case INIT:
>> +        if (process_whitelist
>> +            (seccomp_whitelist_init,
>> +             ARRAY_SIZE(seccomp_whitelist_init), ctx) < 0) {
>> +            rc = -1;
>>               goto seccomp_return;
>>           }
>> -        rc = seccomp_syscall_priority(ctx, seccomp_whitelist[i].num,
>> -                                      seccomp_whitelist[i].priority);
>> -        if (rc < 0) {
>> +        break;
>> +    case MAIN_LOOP:
>> +        if (process_whitelist
>> +            (seccomp_whitelist_main_loop,
>> +             ARRAY_SIZE(seccomp_whitelist_main_loop), ctx) < 0) {
>> +            rc = -1;
>>               goto seccomp_return;
>>           }
>> +        break;
>> +    default:
>> +        rc = -1;
>> +        goto seccomp_return;
>>       }
>>
>>       rc = seccomp_load(ctx);
>> diff --git a/qemu-seccomp.h b/qemu-seccomp.h
>> index b2fc3f8..1c97978 100644
>> --- a/qemu-seccomp.h
>> +++ b/qemu-seccomp.h
>> @@ -18,5 +18,10 @@
>>   #include <seccomp.h>
>>   #include "osdep.h"
>>
>> -int seccomp_start(void);
>> +enum whitelist_mode {
>> +    INIT = 0,
>> +    MAIN_LOOP = 1,
>> +};
>> +
>> +int seccomp_start(enum whitelist_mode mode, scmp_filter_ctx *ctx);
>>   #endif
>> diff --git a/vl.c b/vl.c
>> index bec68cd..773d488 100644
>> --- a/vl.c
>> +++ b/vl.c
>> @@ -278,6 +278,7 @@ static int default_vga = 1;
>>
>>   #ifdef CONFIG_SECCOMP
>>   bool seccomp_on = true;
>> +scmp_filter_ctx ctx;
>
> This should be a local variable to main(), maybe also named
> 'main_loop_ctx' so we can add further contexts.
>
>>   #endif
>>
>>   static struct {
>> @@ -777,7 +778,7 @@ static int bt_parse(const char *opt)
>>   static int install_seccomp_filters(void)
>>   {
>>   #ifdef CONFIG_SECCOMP
>> -    if (seccomp_start() < 0) {
>> +    if (seccomp_start(INIT, &ctx) < 0) {
>>           qerror_report(ERROR_CLASS_GENERIC_ERROR,
>>                   "failed to install seccomp syscall filter in the kernel");
>>           return -1;
>> @@ -3794,6 +3795,16 @@ int main(int argc, char **argv, char **envp)
>>
>>       os_setup_post();
>>
>> +    if (seccomp_on) {
>
> 'seccomp_on' is only available with CONFIG_SECCOMP, so this would break build.
>
>> +#ifdef CONFIG_SECCOMP
>> +        if (seccomp_start(MAIN_LOOP, &ctx) < 0) {
>> +            qerror_report(ERROR_CLASS_GENERIC_ERROR,
>> +                          "failed to install seccomp syscall filter in the kernel");
>
> This error message could be different from the first one.
>
>> +            return -1;
>> +        }
>> +#endif
>> +    }
>> +
>>       resume_all_vcpus();
>>       main_loop();
>>       bdrv_close_all();
>> --
>> 1.7.12
>>
>>
>
>

-- 
Regards,
Corey Bryant