Commit 73a1e647 authored by Eduardo Otubo's avatar Eduardo Otubo
Browse files

seccomp: add elevateprivileges argument to command line 



This patch introduces the new argument
[,elevateprivileges=allow|deny|children] to the `-sandbox on'. It allows
or denies Qemu process to elevate its privileges by blacklisting all
set*uid|gid system calls. The 'children' option will let forks and
execves run unprivileged.

Signed-off-by: default avatarEduardo Otubo <otubo@redhat.com>
parent 2b716fa6

include/sysemu/seccomp.h

+1 −0
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ 


#define QEMU_SECCOMP_SET_DEFAULT     (1 << 0)

#define QEMU_SECCOMP_SET_OBSOLETE    (1 << 1)

#define QEMU_SECCOMP_SET_PRIVILEGED  (1 << 2)



#include <seccomp.h>

qemu-options.hx

+9 −3
Original line number Diff line number Diff line
@@ -4017,20 +4017,26 @@ Old param mode (ARM only). 
ETEXI



DEF("sandbox", HAS_ARG, QEMU_OPTION_sandbox, \

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

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

    "                    C library implementations.\n",

    "                    C library implementations.\n" \

    "                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",

    QEMU_ARCH_ALL)

STEXI

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

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

@item elevateprivileges=@var{string}

Disable set*uid|gid system calls

@end table

ETEXI

qemu-seccomp.c

+11 −0
Original line number Diff line number Diff line
@@ -67,6 +67,17 @@ static const struct QemuSeccompSyscall blacklist[] = { 
    { SCMP_SYS(sysfs),                  QEMU_SECCOMP_SET_OBSOLETE },

    { SCMP_SYS(uselib),                 QEMU_SECCOMP_SET_OBSOLETE },

    { SCMP_SYS(ustat),                  QEMU_SECCOMP_SET_OBSOLETE },

    /* privileged */

    { SCMP_SYS(setuid),                 QEMU_SECCOMP_SET_PRIVILEGED },

    { SCMP_SYS(setgid),                 QEMU_SECCOMP_SET_PRIVILEGED },

    { SCMP_SYS(setpgid),                QEMU_SECCOMP_SET_PRIVILEGED },

    { SCMP_SYS(setsid),                 QEMU_SECCOMP_SET_PRIVILEGED },

    { SCMP_SYS(setreuid),               QEMU_SECCOMP_SET_PRIVILEGED },

    { SCMP_SYS(setregid),               QEMU_SECCOMP_SET_PRIVILEGED },

    { SCMP_SYS(setresuid),              QEMU_SECCOMP_SET_PRIVILEGED },

    { SCMP_SYS(setresgid),              QEMU_SECCOMP_SET_PRIVILEGED },

    { SCMP_SYS(setfsuid),               QEMU_SECCOMP_SET_PRIVILEGED },

    { SCMP_SYS(setfsgid),               QEMU_SECCOMP_SET_PRIVILEGED },

};

vl.c

+27 −0
Original line number Diff line number Diff line
@@ -29,6 +29,7 @@ 


#ifdef CONFIG_SECCOMP

#include "sysemu/seccomp.h"

#include "sys/prctl.h"

#endif



#if defined(CONFIG_VDE)
@@ -275,6 +276,10 @@ static QemuOptsList qemu_sandbox_opts = { 
            .name = "obsolete",

            .type = QEMU_OPT_STRING,

        },

        {

            .name = "elevateprivileges",

            .type = QEMU_OPT_STRING,

        },

        { /* end of list */ }

    },

};
@@ -1056,6 +1061,28 @@ static int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp) 
            }

        }



        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;

            }

        }



        if (seccomp_start(seccomp_opts) < 0) {

            error_report("failed to install seccomp syscall filter "

                         "in the kernel");