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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: Eduardo Otubo <otubo@redhat.com>
This commit is contained in:
Eduardo Otubo 2017-03-13 22:16:01 +01:00
parent 73a1e64725
commit 995a226f88
4 changed files with 28 additions and 2 deletions
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1
include/sysemu/seccomp.h
View File

@ -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>

9
qemu-options.hx
View File

@ -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

4
qemu-seccomp.c
View File

@ -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 },
};

16
vl.c
View File

@ -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");