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Re: [Qemu-devel] [PATCH v3] sandbox: disable -sandbox if CONFIG_SECCOMP

From: Yi Min Zhao
Subject: Re: [Qemu-devel] [PATCH v3] sandbox: disable -sandbox if CONFIG_SECCOMP undefined
Date: Thu, 31 May 2018 11:20:40 +0800
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 


在 2018/5/30 下午6:54, Eduardo Otubo 写道:

On 29/05/2018 - 18:05:25, Yi Min Zhao wrote:


在 2018/5/29 下午5:37, Paolo Bonzini 写道:

On 29/05/2018 09:31, Yi Min Zhao wrote:

If CONFIG_SECCOMP is undefined, the option 'elevateprivileges' remains
compiled. This would make libvirt set the corresponding capability and
then trigger failure during guest startup. This patch moves the code
regarding seccomp command line options to qemu-seccomp.c file and
wraps qemu_opts_foreach finding sandbox option with CONFIG_SECCOMP.
Because parse_sandbox() is moved into qemu-seccomp.c file, change
seccomp_start() to static function.

Signed-off-by: Yi Min Zhao <address@hidden>

I had to squash this in:

diff --git a/vl.c b/vl.c
index 1140feb227..66c17ff8f8 100644
--- a/vl.c
+++ b/vl.c
@@ -3842,11 +3842,16 @@ int main(int argc, char **argv, char **envp)
                   qtest_log = optarg;
                   break;
               case QEMU_OPTION_sandbox:
+#ifndef CONFIG_SECCOMP

One question, I guess you want to use #ifdef ?

Yep, I guess he meant #ifdef.

Can you send a v4 with a cleaned up version? Also fixing a typo on the text
(elevateDprivileges).

Thanks for the contribution.

Sure. Thanks!



                   opts = qemu_opts_parse_noisily(qemu_find_opts("sandbox"),
                                                  optarg, true);
                   if (!opts) {
                       exit(1);
                   }
+#else
+                error_report("-sandbox support is not enabled in this QEMU 
binary");
+                exit(1);
+#endif
                   break;
               case QEMU_OPTION_add_fd:
   #ifndef _WIN32


Otherwise "-sandbox" will crash with a NULL pointer dereference in a binary 
without
seccomp support.  Otherwise looks great, thanks!

Paolo


---
1. Problem Description
======================
If QEMU is built without seccomp support, 'elevateprivileges' remains compiled.
This option of sandbox is treated as an indication for seccomp blacklist support
in libvirt. This behavior is introduced by the libvirt commits 31ca6a5 and
3527f9d. It would make libvirt build wrong QEMU cmdline, and then the guest
startup would fail.

2. Libvirt Log
==============
qemu-system-s390x: -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,\
resourcecontrol=deny: seccomp support is disabled

3. Fixup
========
Move the code related ot sandbox to qemu-seccomp.c file and wrap them with
CONFIG_SECCOMP. So compile the code related to sandbox only when
CONFIG_SECCOMP is defined.
---
   include/sysemu/seccomp.h |   3 +-
   qemu-seccomp.c           | 121 
++++++++++++++++++++++++++++++++++++++++++++++-
   vl.c                     | 118 +--------------------------------------------
   3 files changed, 124 insertions(+), 118 deletions(-)

diff --git a/include/sysemu/seccomp.h b/include/sysemu/seccomp.h
index 9b092aa23f..fe859894f6 100644
--- a/include/sysemu/seccomp.h
+++ b/include/sysemu/seccomp.h
@@ -21,5 +21,6 @@
   #define QEMU_SECCOMP_SET_SPAWN       (1 << 3)
   #define QEMU_SECCOMP_SET_RESOURCECTL (1 << 4)
-int seccomp_start(uint32_t seccomp_opts);
+int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp);
+
   #endif
diff --git a/qemu-seccomp.c b/qemu-seccomp.c
index b770a77d33..148e4c6f24 100644
--- a/qemu-seccomp.c
+++ b/qemu-seccomp.c
@@ -13,6 +13,11 @@
    * GNU GPL, version 2 or (at your option) any later version.
    */
   #include "qemu/osdep.h"
+#include "qemu/config-file.h"
+#include "qemu/option.h"
+#include "qemu/module.h"
+#include "qemu/error-report.h"
+#include <sys/prctl.h>
   #include <seccomp.h>
   #include "sysemu/seccomp.h"
@@ -96,7 +101,7 @@ static const struct QemuSeccompSyscall blacklist[] = {
   };
-int seccomp_start(uint32_t seccomp_opts)
+static int seccomp_start(uint32_t seccomp_opts)
   {
       int rc = 0;
       unsigned int i = 0;
@@ -125,3 +130,117 @@ int seccomp_start(uint32_t seccomp_opts)
       seccomp_release(ctx);
       return rc;
   }
+
+#ifdef CONFIG_SECCOMP
+int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp)
+{
+    if (qemu_opt_get_bool(opts, "enable", false)) {
+        uint32_t seccomp_opts = QEMU_SECCOMP_SET_DEFAULT
+                | QEMU_SECCOMP_SET_OBSOLETE;
+        const char *value = NULL;
+
+        value = qemu_opt_get(opts, "obsolete");
+        if (value) {
+            if (g_str_equal(value, "allow")) {
+                seccomp_opts &= ~QEMU_SECCOMP_SET_OBSOLETE;
+            } else if (g_str_equal(value, "deny")) {
+                /* this is the default option, this if is here
+                 * to provide a little bit of consistency for
+                 * the command line */
+            } else {
+                error_report("invalid argument for obsolete");
+                return -1;
+            }
+        }
+
+        value = qemu_opt_get(opts, "elevateprivileges");
+        if (value) {
+            if (g_str_equal(value, "deny")) {
+                seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
+            } else if (g_str_equal(value, "children")) {
+                seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
+
+                /* calling prctl directly because we're
+                 * not sure if host has CAP_SYS_ADMIN set*/
+                if (prctl(PR_SET_NO_NEW_PRIVS, 1)) {
+                    error_report("failed to set no_new_privs "
+                                 "aborting");
+                    return -1;
+                }
+            } else if (g_str_equal(value, "allow")) {
+                /* default value */
+            } else {
+                error_report("invalid argument for elevateprivileges");
+                return -1;
+            }
+        }
+
+        value = qemu_opt_get(opts, "spawn");
+        if (value) {
+            if (g_str_equal(value, "deny")) {
+                seccomp_opts |= QEMU_SECCOMP_SET_SPAWN;
+            } else if (g_str_equal(value, "allow")) {
+                /* default value */
+            } else {
+                error_report("invalid argument for spawn");
+                return -1;
+            }
+        }
+
+        value = qemu_opt_get(opts, "resourcecontrol");
+        if (value) {
+            if (g_str_equal(value, "deny")) {
+                seccomp_opts |= QEMU_SECCOMP_SET_RESOURCECTL;
+            } else if (g_str_equal(value, "allow")) {
+                /* default value */
+            } else {
+                error_report("invalid argument for resourcecontrol");
+                return -1;
+            }
+        }
+
+        if (seccomp_start(seccomp_opts) < 0) {
+            error_report("failed to install seccomp syscall filter "
+                         "in the kernel");
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+static QemuOptsList qemu_sandbox_opts = {
+    .name = "sandbox",
+    .implied_opt_name = "enable",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_sandbox_opts.head),
+    .desc = {
+        {
+            .name = "enable",
+            .type = QEMU_OPT_BOOL,
+        },
+        {
+            .name = "obsolete",
+            .type = QEMU_OPT_STRING,
+        },
+        {
+            .name = "elevateprivileges",
+            .type = QEMU_OPT_STRING,
+        },
+        {
+            .name = "spawn",
+            .type = QEMU_OPT_STRING,
+        },
+        {
+            .name = "resourcecontrol",
+            .type = QEMU_OPT_STRING,
+        },
+        { /* end of list */ }
+    },
+};
+
+static void seccomp_register(void)
+{
+    qemu_add_opts(&qemu_sandbox_opts);
+}
+opts_init(seccomp_register);
+#endif
diff --git a/vl.c b/vl.c
index 806eec2ef6..ea04aa2e2b 100644
--- a/vl.c
+++ b/vl.c
@@ -28,11 +28,7 @@
   #include "qemu/cutils.h"
   #include "qemu/help_option.h"
   #include "qemu/uuid.h"
-
-#ifdef CONFIG_SECCOMP
-#include <sys/prctl.h>
   #include "sysemu/seccomp.h"
-#endif
   #ifdef CONFIG_SDL
   #if defined(__APPLE__) || defined(main)
@@ -257,35 +253,6 @@ static QemuOptsList qemu_rtc_opts = {
       },
   };
-static QemuOptsList qemu_sandbox_opts = {
-    .name = "sandbox",
-    .implied_opt_name = "enable",
-    .head = QTAILQ_HEAD_INITIALIZER(qemu_sandbox_opts.head),
-    .desc = {
-        {
-            .name = "enable",
-            .type = QEMU_OPT_BOOL,
-        },
-        {
-            .name = "obsolete",
-            .type = QEMU_OPT_STRING,
-        },
-        {
-            .name = "elevateprivileges",
-            .type = QEMU_OPT_STRING,
-        },
-        {
-            .name = "spawn",
-            .type = QEMU_OPT_STRING,
-        },
-        {
-            .name = "resourcecontrol",
-            .type = QEMU_OPT_STRING,
-        },
-        { /* end of list */ }
-    },
-};
-
   static QemuOptsList qemu_option_rom_opts = {
       .name = "option-rom",
       .implied_opt_name = "romfile",
@@ -1041,88 +1008,6 @@ static int bt_parse(const char *opt)
       return 1;
   }
-static int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp)
-{
-    if (qemu_opt_get_bool(opts, "enable", false)) {
-#ifdef CONFIG_SECCOMP
-        uint32_t seccomp_opts = QEMU_SECCOMP_SET_DEFAULT
-                | QEMU_SECCOMP_SET_OBSOLETE;
-        const char *value = NULL;
-
-        value = qemu_opt_get(opts, "obsolete");
-        if (value) {
-            if (g_str_equal(value, "allow")) {
-                seccomp_opts &= ~QEMU_SECCOMP_SET_OBSOLETE;
-            } else if (g_str_equal(value, "deny")) {
-                /* this is the default option, this if is here
-                 * to provide a little bit of consistency for
-                 * the command line */
-            } else {
-                error_report("invalid argument for obsolete");
-                return -1;
-            }
-        }
-
-        value = qemu_opt_get(opts, "elevateprivileges");
-        if (value) {
-            if (g_str_equal(value, "deny")) {
-                seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
-            } else if (g_str_equal(value, "children")) {
-                seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
-
-                /* calling prctl directly because we're
-                 * not sure if host has CAP_SYS_ADMIN set*/
-                if (prctl(PR_SET_NO_NEW_PRIVS, 1)) {
-                    error_report("failed to set no_new_privs "
-                                 "aborting");
-                    return -1;
-                }
-            } else if (g_str_equal(value, "allow")) {
-                /* default value */
-            } else {
-                error_report("invalid argument for elevateprivileges");
-                return -1;
-            }
-        }
-
-        value = qemu_opt_get(opts, "spawn");
-        if (value) {
-            if (g_str_equal(value, "deny")) {
-                seccomp_opts |= QEMU_SECCOMP_SET_SPAWN;
-            } else if (g_str_equal(value, "allow")) {
-                /* default value */
-            } else {
-                error_report("invalid argument for spawn");
-                return -1;
-            }
-        }
-
-        value = qemu_opt_get(opts, "resourcecontrol");
-        if (value) {
-            if (g_str_equal(value, "deny")) {
-                seccomp_opts |= QEMU_SECCOMP_SET_RESOURCECTL;
-            } else if (g_str_equal(value, "allow")) {
-                /* default value */
-            } else {
-                error_report("invalid argument for resourcecontrol");
-                return -1;
-            }
-        }
-
-        if (seccomp_start(seccomp_opts) < 0) {
-            error_report("failed to install seccomp syscall filter "
-                         "in the kernel");
-            return -1;
-        }
-#else
-        error_report("seccomp support is disabled");
-        return -1;
-#endif
-    }
-
-    return 0;
-}
-
   static int parse_name(void *opaque, QemuOpts *opts, Error **errp)
   {
       const char *proc_name;
@@ -3074,7 +2959,6 @@ int main(int argc, char **argv, char **envp)
       qemu_add_opts(&qemu_mem_opts);
       qemu_add_opts(&qemu_smp_opts);
       qemu_add_opts(&qemu_boot_opts);
-    qemu_add_opts(&qemu_sandbox_opts);
       qemu_add_opts(&qemu_add_fd_opts);
       qemu_add_opts(&qemu_object_opts);
       qemu_add_opts(&qemu_tpmdev_opts);
@@ -4071,10 +3955,12 @@ int main(int argc, char **argv, char **envp)
           exit(1);
       }
+#ifdef CONFIG_SECCOMP
       if (qemu_opts_foreach(qemu_find_opts("sandbox"),
                             parse_sandbox, NULL, NULL)) {
           exit(1);
       }
+#endif
       if (qemu_opts_foreach(qemu_find_opts("name"),
                             parse_name, NULL, NULL)) {
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