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Disallow clone3, unsafe clone and unshare flags

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Ability to create new namespaces and getting capabilities in there exposes a big kernel attack surface.

PiperOrigin-RevId: 564703131
Change-Id: I3dcf4c78dca9f51a4b068df16e1b1a69916d727c
This commit is contained in:
Wiktor Garbacz 2023-09-12 06:29:54 -07:00 committed by Copybara-Service
parent 77f62ccb1f
commit 4289b64aa7
1 changed files with 26 additions and 4 deletions
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30
sandboxed_api/sandbox2/policy.cc
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@ -25,6 +25,7 @@
#include <syscall.h> #include <syscall.h>
#include <cstdint> #include <cstdint>
#include <limits>
#include <optional> #include <optional>
#include <string> #include <string>
#include <vector> #include <vector>
@ -170,16 +171,37 @@ std::vector<sock_filter> Policy::GetDefaultPolicy(bool user_notif) const {
if (!user_policy_handles_bpf_) { if (!user_policy_handles_bpf_) {
policy.insert(policy.end(), {JEQ32(__NR_bpf, DENY)}); policy.insert(policy.end(), {JEQ32(__NR_bpf, DENY)});
} }
#ifndef CLONE_NEWCGROUP
#define CLONE_NEWCGROUP 0x02000000
#endif
constexpr uintptr_t kNewNamespacesFlags =
CLONE_NEWNS | CLONE_NEWUSER | CLONE_NEWNET | CLONE_NEWUTS |
CLONE_NEWCGROUP | CLONE_NEWIPC | CLONE_NEWPID;
static_assert(kNewNamespacesFlags <= std::numeric_limits<uint32_t>::max());
constexpr uintptr_t kUnsafeCloneFlags = kNewNamespacesFlags | CLONE_UNTRACED;
static_assert(kUnsafeCloneFlags <= std::numeric_limits<uint32_t>::max());
policy.insert(policy.end(), policy.insert(policy.end(),
{ {
// Disallow clone with CLONE_UNTRACED flag. This uses #ifdef __NR_clone3
// Disallow clone3
JEQ32(__NR_clone3, DENY),
#endif
// Disallow clone3 and clone with unsafe flags. This uses
// LOAD_SYSCALL_NR from above. // LOAD_SYSCALL_NR from above.
JNE32(__NR_clone, JUMP(&l, past_clone_untraced_l)), JNE32(__NR_clone, JUMP(&l, past_clone_unsafe_l)),
// Regardless of arch, we only care about the lower 32-bits // Regardless of arch, we only care about the lower 32-bits
// of the flags. // of the flags.
ARG_32(0), ARG_32(0),
JA32(CLONE_UNTRACED, DENY), JA32(kUnsafeCloneFlags, DENY),
LABEL(&l, past_clone_untraced_l), LABEL(&l, past_clone_unsafe_l),
// Disallow unshare with unsafe flags.
LOAD_SYSCALL_NR,
JNE32(__NR_unshare, JUMP(&l, past_unshare_unsafe_l)),
// Regardless of arch, we only care about the lower 32-bits
// of the flags.
ARG_32(0),
JA32(kNewNamespacesFlags, DENY),
LABEL(&l, past_unshare_unsafe_l),
// Disallow seccomp with SECCOMP_FILTER_FLAG_NEW_LISTENER // Disallow seccomp with SECCOMP_FILTER_FLAG_NEW_LISTENER
// flag. // flag.
LOAD_SYSCALL_NR, LOAD_SYSCALL_NR,