Re: [Qemu-devel] [PATCHv2 3/4] Support for "double whitelist" filters

[Corey Bryant]

On 10/23/2012 01:55 AM, Eduardo Otubo 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.

v2: * ctx changed to main_loop_ctx
     * seccomp_on now inside ifdef
     * open syscall added to the main_loop whitelist

Signed-off-by: Eduardo Otubo <ot...@linux.vnet.ibm.com>
---
  qemu-seccomp.c | 99 ++++++++++++++++++++++++++++++++++++++++++++++++++++------
  qemu-seccomp.h |  7 ++++-
  vl.c           | 21 +++++++++++--
  3 files changed, 114 insertions(+), 13 deletions(-)

diff --git a/qemu-seccomp.c b/qemu-seccomp.c
index a7b33e2..033cfad 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 },
@@ -121,27 +122,107 @@ static const struct QemuSeccompSyscall 
seccomp_whitelist[] = {
      { SCMP_SYS(rt_sigtimedwait), 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 },
+    { SCMP_SYS(open), 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 },
+    { SCMP_SYS(eventfd2), 242 },
+    { SCMP_SYS(recvmsg), 242 },
+    { SCMP_SYS(ioctl), 242 },
+    { SCMP_SYS(rt_sigprocmask), 242 }
+};
+
+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);

Is there any reason why ctx can't be a local variable in this function? 
 It is allocated and freed on each entry and exit in this function.

      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..d50018f 100644
--- a/vl.c
+++ b/vl.c
@@ -774,10 +774,11 @@ static int bt_parse(const char *opt)
      return 1;
  }

-static int install_seccomp_filters(void)
+static int
+install_seccomp_filters(enum whitelist_mode mode, scmp_filter_ctx *ctx)
  {
  #ifdef CONFIG_SECCOMP
-    if (seccomp_start() < 0) {
+    if (seccomp_start(mode, ctx) < 0) {
          qerror_report(ERROR_CLASS_GENERIC_ERROR,
                  "failed to install seccomp syscall filter in the kernel");

I heard from Luiz Capitulino on one of my patches that qerror_report() 
is deprecated.  So you'll want to update this.

          return -1;
@@ -2407,6 +2408,10 @@ int main(int argc, char **argv, char **envp)
      const char *trace_events = NULL;
      const char *trace_file = NULL;

+#ifdef CONFIG_SECCOMP
+    scmp_filter_ctx main_loop_ctx;
+#endif
+
      atexit(qemu_run_exit_notifiers);
      error_set_progname(argv[0]);

@@ -3330,11 +3335,13 @@ int main(int argc, char **argv, char **envp)
      }

      /* We should install seccomp filters even if -sandbox on is not used. */
+#ifdef CONFIG_SECCOMP
      if (seccomp_on) {
-        if (install_seccomp_filters() < 0) {
+        if (install_seccomp_filters(INIT, &main_loop_ctx) < 0) {

I don't think the variable name "main_loop_ctx" makes sense here. 
Should the name be more generic since it's used wherever a seccomp 
filter is installed?

              exit(1);
          }
      }
+#endif

      if (machine == NULL) {
          fprintf(stderr, "No machine found.\n");
@@ -3794,6 +3801,14 @@ int main(int argc, char **argv, char **envp)

      os_setup_post();

+#ifdef CONFIG_SECCOMP
+    if (seccomp_on) {
+        if (install_seccomp_filters(MAIN_LOOP, &main_loop_ctx) < 0) {
+            exit(1);
+        }
+    }
+#endif
+
      resume_all_vcpus();
      main_loop();
      bdrv_close_all();


--
Regards,
Corey Bryant