seccomp: add obsolete option

This patch introduces the argument [,obsolete=allow] to the -sandbox
option. It allows Qemu to run safely on old system that still relies on
old system calls.

Signed-off-by: Eduardo Otubo <eduardo.otubo@profitbricks.com>

include/sysemu/seccomp.h

@@ -17,5 +17,5 @@
 
 #include <seccomp.h>
 
-int seccomp_start(void);
+int seccomp_start(unsigned int obsolete);
 #endif

qemu-options.hx

@@ -3702,13 +3702,18 @@ Old param mode (ARM only).
 ETEXI
 
 DEF("sandbox", HAS_ARG, QEMU_OPTION_sandbox, \
-    "-sandbox <arg>  Enable seccomp mode 2 system call filter (default 'off').\n",
+    "-sandbox on[,obsolete=allow]  Enable seccomp mode 2 system call filter (default 'off').\n" \
+    "                              obsolete: Allow obsolete system calls",
     QEMU_ARCH_ALL)
 STEXI
-@item -sandbox @var{arg}
+@item -sandbox @var{arg}[,obsolete=@var{string}]
 @findex -sandbox
 Enable Seccomp mode 2 system call filter. 'on' will enable syscall filtering and 'off' will
 disable it.  The default is 'off'.
+@table @option
+@item obsolete=@var{string}
+Enable Obsolete system calls
+@end table
 ETEXI
 
 DEF("readconfig", HAS_ARG, QEMU_OPTION_readconfig,

qemu-seccomp.c

@@ -31,7 +31,12 @@ struct QemuSeccompSyscall {
     uint8_t priority;
 };
 
+static const struct QemuSeccompSyscall obsolete[] = {
+    { SCMP_SYS(readdir), 255 },
+};
+
 static const struct QemuSeccompSyscall blacklist[] = {
+    { SCMP_SYS(readdir), 255 },
     { SCMP_SYS(reboot), 255 },
     { SCMP_SYS(swapon), 255 },
     { SCMP_SYS(swapoff), 255 },
@@ -56,7 +61,20 @@ static const struct QemuSeccompSyscall blacklist[] = {
     { SCMP_SYS(vserver), 255 },
 };
 
-int seccomp_start(void)
+static int is_obsolete(int syscall)
+{
+    unsigned int i = 0;
+
+    for (i = 0; i < ARRAY_SIZE(obsolete); i++) {
+        if (syscall == obsolete[i].num) {
+            return 1;
+        }
+    }
+
+    return 0;
+}
+
+int seccomp_start(unsigned int obsolete)
 {
     int rc = 0;
     unsigned int i = 0;
@@ -69,6 +87,11 @@ int seccomp_start(void)
     }
 
     for (i = 0; i < ARRAY_SIZE(blacklist); i++) {
+        if (obsolete) {
+            if(is_obsolete(blacklist[i].num)) {
+                continue;
+            }
+        }
         rc = seccomp_rule_add(ctx, SCMP_ACT_KILL, blacklist[i].num, 0);
         if (rc < 0) {
             goto seccomp_return;

vl.c

@@ -265,6 +265,10 @@ static QemuOptsList qemu_sandbox_opts = {
             .name = "enable",
             .type = QEMU_OPT_BOOL,
         },
+        {
+            .name = "obsolete",
+            .type = QEMU_OPT_STRING,
+        },
         { /* end of list */ }
     },
 };
@@ -1027,7 +1031,11 @@ static int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp)
     /* FIXME: change this to true for 1.3 */
     if (qemu_opt_get_bool(opts, "enable", false)) {
 #ifdef CONFIG_SECCOMP
-        if (seccomp_start() < 0) {
+        unsigned int obsolete = 0;
+
+        if (strcmp(qemu_opt_get(opts,"obsolete"), "allow") == 0) obsolete = 1;
+
+        if (seccomp_start(obsolete) < 0) {
             error_report("failed to install seccomp syscall filter "
                          "in the kernel");
             return -1;