Commit 995a226f authored by Eduardo Otubo's avatar Eduardo Otubo
Browse files

seccomp: add spawn argument to command line 



This patch adds [,spawn=deny] argument to `-sandbox on' option. It
blacklists fork and execve system calls, avoiding Qemu to spawn new
threads or processes.

Signed-off-by: default avatarEduardo Otubo <otubo@redhat.com>
parent 73a1e647

include/sysemu/seccomp.h

+1 −0
Original line number Diff line number Diff line
@@ -18,6 +18,7 @@ 
#define QEMU_SECCOMP_SET_DEFAULT     (1 << 0)

#define QEMU_SECCOMP_SET_OBSOLETE    (1 << 1)

#define QEMU_SECCOMP_SET_PRIVILEGED  (1 << 2)

#define QEMU_SECCOMP_SET_SPAWN       (1 << 3)



#include <seccomp.h>

qemu-options.hx

+7 −2
Original line number Diff line number Diff line
@@ -4018,6 +4018,7 @@ ETEXI 


DEF("sandbox", HAS_ARG, QEMU_OPTION_sandbox, \

    "-sandbox on[,obsolete=allow|deny][,elevateprivileges=allow|deny|children]\n" \

    "          [,spawn=allow|deny]\n" \

    "                Enable seccomp mode 2 system call filter (default 'off').\n" \

    "                use 'obsolete' to allow obsolete system calls that are provided\n" \

    "                    by the kernel, but typically no longer used by modern\n" \
@@ -4025,10 +4026,12 @@ DEF("sandbox", HAS_ARG, QEMU_OPTION_sandbox, \ 
    "                use 'elevateprivileges' to allow or deny QEMU process to elevate\n" \

    "                    its privileges by blacklisting all set*uid|gid system calls.\n" \

    "                    The value 'children' will deny set*uid|gid system calls for\n" \

    "                    main QEMU process but will allow forks and execves to run unprivileged\n",

    "                    main QEMU process but will allow forks and execves to run unprivileged\n" \

    "                use 'spawn' to avoid QEMU to spawn new threads or processes by\n" \

    "                     blacklisting *fork and execve\n",

    QEMU_ARCH_ALL)

STEXI

@item -sandbox @var{arg}[,obsolete=@var{string}][,elevateprivileges=@var{string}]

@item -sandbox @var{arg}[,obsolete=@var{string}][,elevateprivileges=@var{string}][,spawn=@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'.
@@ -4037,6 +4040,8 @@ disable it. The default is 'off'. 
Enable Obsolete system calls

@item elevateprivileges=@var{string}

Disable set*uid|gid system calls

@item spawn=@var{string}

Disable *fork and execve

@end table

ETEXI

qemu-seccomp.c

+4 −0
Original line number Diff line number Diff line
@@ -78,6 +78,10 @@ static const struct QemuSeccompSyscall blacklist[] = { 
    { SCMP_SYS(setresgid),              QEMU_SECCOMP_SET_PRIVILEGED },

    { SCMP_SYS(setfsuid),               QEMU_SECCOMP_SET_PRIVILEGED },

    { SCMP_SYS(setfsgid),               QEMU_SECCOMP_SET_PRIVILEGED },

    /* spawn */

    { SCMP_SYS(fork),                   QEMU_SECCOMP_SET_SPAWN },

    { SCMP_SYS(vfork),                  QEMU_SECCOMP_SET_SPAWN },

    { SCMP_SYS(execve),                 QEMU_SECCOMP_SET_SPAWN },

};

vl.c

+16 −0
Original line number Diff line number Diff line
@@ -280,6 +280,10 @@ static QemuOptsList qemu_sandbox_opts = { 
            .name = "elevateprivileges",

            .type = QEMU_OPT_STRING,

        },

        {

            .name = "spawn",

            .type = QEMU_OPT_STRING,

        },

        { /* end of list */ }

    },

};
@@ -1083,6 +1087,18 @@ static int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp) 
            }

        }



        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;

            }

        }



        if (seccomp_start(seccomp_opts) < 0) {

            error_report("failed to install seccomp syscall filter "

                         "in the kernel");