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From:   Hengqi Chen <hengqi.chen@gmail.com>
To:     linux-kernel@vger.kernel.org, bpf@vger.kernel.org
Cc:     keescook@chromium.org, luto@amacapital.net, wad@chromium.org,
        alexyonghe@tencent.com, hengqi.chen@gmail.com
Subject: [RFC PATCH 1/2] seccomp: Introduce SECCOMP_LOAD_FILTER operation
Date:   Tue,  3 Oct 2023 08:38:35 +0000
Message-Id: <20231003083836.100706-2-hengqi.chen@gmail.com>
In-Reply-To: <20231003083836.100706-1-hengqi.chen@gmail.com>
References: <20231003083836.100706-1-hengqi.chen@gmail.com>
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This patch adds a new operation named SECCOMP_LOAD_FILTER.
It accepts the same arguments as SECCOMP_SET_MODE_FILTER
but only performs the loading process. If succeed, return a
new fd associated with the JITed BPF program (the filter).
The filter can then be pinned to bpffs using the returned
fd and reused for different processes.

Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
---
 include/uapi/linux/seccomp.h |  1 +
 kernel/seccomp.c             | 64 ++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)

diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
index dbfc9b37fcae..ee2c83697810 100644
--- a/include/uapi/linux/seccomp.h
+++ b/include/uapi/linux/seccomp.h
@@ -16,6 +16,7 @@
 #define SECCOMP_SET_MODE_FILTER		1
 #define SECCOMP_GET_ACTION_AVAIL	2
 #define SECCOMP_GET_NOTIF_SIZES		3
+#define SECCOMP_LOAD_FILTER		4
 
 /* Valid flags for SECCOMP_SET_MODE_FILTER */
 #define SECCOMP_FILTER_FLAG_TSYNC		(1UL << 0)
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 255999ba9190..7aff22f56a91 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -1996,12 +1996,71 @@ static long seccomp_set_mode_filter(unsigned int flags,
 	seccomp_filter_free(prepared);
 	return ret;
 }
+
+static long seccomp_load_filter(const char __user *filter)
+{
+	struct sock_fprog fprog;
+	struct bpf_prog *prog;
+	int ret = -EFAULT;
+	const bool save_orig =
+#if defined(CONFIG_CHECKPOINT_RESTORE) || defined(SECCOMP_ARCH_NATIVE)
+		true;
+#else
+		false;
+#endif
+
+#ifdef CONFIG_COMPAT
+	if (in_compat_syscall()) {
+		struct compat_sock_fprog fprog32;
+		if (copy_from_user(&fprog32, filter, sizeof(fprog32)))
+			goto out;
+		fprog.len = fprog32.len;
+		fprog.filter = compat_ptr(fprog32.filter);
+	} else /* falls through to the if below. */
+#endif
+	if (copy_from_user(&fprog, filter, sizeof(fprog)))
+		goto out;
+
+	ret = -EINVAL;
+	if (fprog.len == 0 || fprog.len > BPF_MAXINSNS)
+		goto out;
+
+	BUG_ON(INT_MAX / fprog.len < sizeof(struct sock_filter));
+
+	ret = bpf_prog_create_from_user(&prog, &fprog, seccomp_check_filter, save_orig);
+	if (ret < 0)
+		goto out;
+
+	ret = security_bpf_prog_alloc(prog->aux);
+	if (ret) {
+		ret = -EINVAL;
+		goto prog_free;
+	}
+
+	prog->aux->user = get_current_user();
+	atomic64_set(&prog->aux->refcnt, 1);
+
+	ret = bpf_prog_new_fd(prog);
+	if (ret < 0)
+		bpf_prog_put(prog);
+	return ret;
+
+prog_free:
+	bpf_prog_free(prog);
+out:
+	return ret;
+}
 #else
 static inline long seccomp_set_mode_filter(unsigned int flags,
 					   const char __user *filter)
 {
 	return -EINVAL;
 }
+
+static inline long seccomp_load_filter(const char __user *filter)
+{
+	return -EINVAL;
+}
 #endif
 
 static long seccomp_get_action_avail(const char __user *uaction)
@@ -2063,6 +2122,11 @@ static long do_seccomp(unsigned int op, unsigned int flags,
 			return -EINVAL;
 
 		return seccomp_get_notif_sizes(uargs);
+	case SECCOMP_LOAD_FILTER:
+		if (flags != 0)
+			return -EINVAL;
+
+		return seccomp_load_filter(uargs);
 	default:
 		return -EINVAL;
 	}
-- 
2.34.1