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 <ot...@redhat.com>
---
include/sysemu/seccomp.h | 1 +
qemu-options.hx | 5 ++++-
qemu-seccomp.c | 19 +++++++++++++++++++
vl.c | 11 +++++++++++
4 files changed, 35 insertions(+), 1 deletion(-)
diff --git a/include/sysemu/seccomp.h b/include/sysemu/seccomp.h
index e6e78d85ce..f1614d6514 100644
--- a/include/sysemu/seccomp.h
+++ b/include/sysemu/seccomp.h
@@ -17,6 +17,7 @@
#define OBSOLETE 0x0001
#define PRIVILEGED 0x0010
+#define SPAWN 0x0100
#include <seccomp.h>
diff --git a/qemu-options.hx b/qemu-options.hx
index 6dc776aae3..611a501684 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4004,10 +4004,11 @@ Old param mode (ARM only).
ETEXI
DEF("sandbox", HAS_ARG, QEMU_OPTION_sandbox, \
- "-sandbox on[,obsolete=allow][,elevateprivileges=allow|deny|children]\n" \
+ "-sandbox
on[,obsolete=allow][,elevateprivileges=allow|deny|children][,spawn=deny]\n" \
" Enable seccomp mode 2 system call filter
(default 'off').\n" \
" obsolete: Allow obsolete system calls\n" \
" elevateprivileges: allows or denies Qemu
process to elevate its privileges by blacklisting all set*uid|gid system calls.
'children' will deny set*uid|gid system calls for main Qemu process but will
allow forks and execves to run unprivileged",
+ " spawn: avoids Qemu to spawn new threads or
processes by blacklisting *fork and execve\n"
QEMU_ARCH_ALL)
STEXI
@item -sandbox @var{arg}[,obsolete=@var{string}]
@@ -4019,6 +4020,8 @@ disable it. The default is 'off'.
Enable Obsolete system calls
@item elevateprivileges=@var{string}
Disable set*uid|gid systema calls
+@item spawn=@var{string}
+Disable *fork and execve
@end table
ETEXI
diff --git a/qemu-seccomp.c b/qemu-seccomp.c
index c204cef9ee..075d87e27f 100644
--- a/qemu-seccomp.c
+++ b/qemu-seccomp.c
@@ -31,6 +31,12 @@ struct QemuSeccompSyscall {
uint8_t priority;
};
+static const struct QemuSeccompSyscall spawn_syscalls[] = {
+ { SCMP_SYS(fork), 255 },
+ { SCMP_SYS(vfork), 255 },
+ { SCMP_SYS(execve), 255 },
+};
+
static const struct QemuSeccompSyscall privileged_syscalls[] = {
{ SCMP_SYS(setuid), 255 },
{ SCMP_SYS(setgid), 255 },
@@ -138,6 +144,19 @@ int seccomp_start(uint8_t seccomp_opts)
}
}
+ if (seccomp_opts & SPAWN) {
+ for (i = 0; i < ARRAY_SIZE(spawn_syscalls); i++) {
+ rc = seccomp_rule_add(ctx, SCMP_ACT_KILL, spawn_syscalls[i].num,
0);
+ if (rc < 0) {
+ goto seccomp_return;
+ }
+ rc = seccomp_syscall_priority(ctx, spawn_syscalls[i].num,
+ spawn_syscalls[i].priority);
+ if (rc < 0) {
+ goto seccomp_return;
+ }
+ }
+ }
rc = seccomp_load(ctx);
diff --git a/vl.c b/vl.c
index 0b857083a3..456a518431 100644
--- a/vl.c
+++ b/vl.c
@@ -279,6 +279,10 @@ static QemuOptsList qemu_sandbox_opts = {
.name = "elevateprivileges",
.type = QEMU_OPT_STRING,
},
+ {
+ .name = "spawn",
+ .type = QEMU_OPT_STRING,
+ },
{ /* end of list */ }
},
};
@@ -1064,6 +1068,13 @@ static int parse_sandbox(void *opaque, QemuOpts *opts,
Error **errp)
}
}
+ value = qemu_opt_get(opts,"spawn");
+ if (value) {
+ if (strcmp(value, "deny") == 0) {
+ seccomp_opts |= SPAWN;
+ }
+ }
+
if (seccomp_start(seccomp_opts) < 0) {
error_report("failed to install seccomp syscall filter "
"in the kernel");
--
2.13.0
