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

[Eduardo Otubo <otubo@linux.vnet.ibm.com>]

On Tue, Oct 23, 2012 at 11:10:58AM -0400, Corey Bryant wrote:
> 
> 
> 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 <otubo@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.

I think you're probaby right. I'll declare this variable as local in the
next version.

> 
> >      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?

I removed this variable since I'm using a local variable as I said
above.

Thanks for the comments :)

-- 
Eduardo Otubo
Software Engineer
Linux Technology Center
IBM Systems & Technology Group