This patch adds [,spawn=deny] argument to `-sandbox on' option. It blacklists fork and execve syste calls, avoiding Qemu to spawn new threads or processes.
Signed-off-by: Eduardo Otubo <[email protected]> --- include/sysemu/seccomp.h | 1 + qemu-options.hx | 7 +++++-- qemu-seccomp.c | 18 ++++++++++++++++++ vl.c | 11 +++++++++++ 4 files changed, 35 insertions(+), 2 deletions(-) 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 47018db5aa..53f4f8cfd2 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -3732,10 +3732,11 @@ Old param mode (ARM only). ETEXI DEF("sandbox", HAS_ARG, QEMU_OPTION_sandbox, \ - "-sandbox on[,obsolete=allow][,elevateprivileges=deny]\n" \ + "-sandbox on[,obsolete=allow][,elevateprivileges=deny][,spawn=deny]" \ " Enable seccomp mode 2 system call filter (default 'off').\n" \ " obsolete: Allow obsolete system calls\n" \ - " elevateprivileges: avoids Qemu process to elevate its privileges by blacklisting all set*uid|gid system calls", + " elevateprivileges: avoids Qemu process to elevate its privileges by blacklisting all set*uid|gid system calls\n" \ + " 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}] @@ -3747,6 +3748,8 @@ 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 5aa6590386..4c1f7b41ba 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 }, @@ -152,6 +158,18 @@ 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 d071e240b0..6a6e9a69bf 100644 --- a/vl.c +++ b/vl.c @@ -277,6 +277,10 @@ static QemuOptsList qemu_sandbox_opts = { .name = "elevateprivileges", .type = QEMU_OPT_STRING, }, + { + .name = "spawn", + .type = QEMU_OPT_STRING, + }, { /* end of list */ } }, }; @@ -1056,6 +1060,13 @@ 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"); -- 2.11.0
