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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: Eduardo Otubo <otubo@redhat.com>
This commit is contained in:
Eduardo Otubo 2017-03-13 22:13:27 +01:00
parent 2b716fa6d6
commit 73a1e64725
4 changed files with 48 additions and 3 deletions
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1
include/sysemu/seccomp.h
View File

@ -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>

12
qemu-options.hx
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@ -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

11
qemu-seccomp.c
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@ -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 },
};

27
vl.c
View File

@ -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");