From c542b302707628609f2a33bcbd3e442282806b8e Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Thu, 29 Jul 2021 16:43:01 +0100 Subject: [PATCH] seccomp: block use of clone3 syscall MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Modern glibc will use clone3 instead of clone, when it detects that it is available. We need to compare flags in order to decide whether to allow clone (thread create vs process fork), but in clone3 the flags are hidden inside a struct. Seccomp can't currently match on data inside a struct, so our only option is to block clone3 entirely. If we use ENOSYS to block it, then glibc transparently falls back to clone. This may need to be revisited if Linux adds a new architecture in future and only provides clone3, without clone. Acked-by: Eduardo Otubo Signed-off-by: Daniel P. Berrangé --- softmmu/qemu-seccomp.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/softmmu/qemu-seccomp.c b/softmmu/qemu-seccomp.c index 57139cc9ce..a7bb5c350f 100644 --- a/softmmu/qemu-seccomp.c +++ b/softmmu/qemu-seccomp.c @@ -244,6 +244,10 @@ static const struct QemuSeccompSyscall denylist[] = { RULE_CLONE_FLAG(CLONE_NEWPID), RULE_CLONE_FLAG(CLONE_NEWNET), RULE_CLONE_FLAG(CLONE_IO), +#ifdef __SNR_clone3 + { SCMP_SYS(clone3), QEMU_SECCOMP_SET_SPAWN, + 0, NULL, SCMP_ACT_ERRNO(ENOSYS) }, +#endif /* resource control */ { SCMP_SYS(setpriority), QEMU_SECCOMP_SET_RESOURCECTL, 0, NULL, SCMP_ACT_ERRNO(EPERM) },