[PATCH v2 3/5] seccomp: Introduce new flag SECCOMP_FILTER_FLAG_BPF_PROG_FD

[Hengqi Chen <hengqi.chen@gmail.com>]

Add a new flag SECCOMP_FILTER_FLAG_BPF_PROG_FD for
SECCOMP_SET_MODE_FILTER. This indicates the seccomp filter
is a seccomp bpf prog fd, not a sock_fprog. This allows
us to attach the seccomp filter that is previously loaded
via SECCOMP_LOAD_FILTER.

Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
---
 include/linux/seccomp.h      |  3 ++-
 include/uapi/linux/seccomp.h |  2 ++
 kernel/seccomp.c             | 37 ++++++++++++++++++++++++++++++++++--
 3 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index 175079552f68..7caa53b629d9 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -9,7 +9,8 @@
 					 SECCOMP_FILTER_FLAG_SPEC_ALLOW | \
 					 SECCOMP_FILTER_FLAG_NEW_LISTENER | \
 					 SECCOMP_FILTER_FLAG_TSYNC_ESRCH | \
-					 SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV)
+					 SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV | \
+					 SECCOMP_FILTER_FLAG_BPF_PROG_FD)
 
 /* sizeof() the first published struct seccomp_notif_addfd */
 #define SECCOMP_NOTIFY_ADDFD_SIZE_VER0 24
diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
index ee2c83697810..d6b243d1b4d5 100644
--- a/include/uapi/linux/seccomp.h
+++ b/include/uapi/linux/seccomp.h
@@ -26,6 +26,8 @@
 #define SECCOMP_FILTER_FLAG_TSYNC_ESRCH		(1UL << 4)
 /* Received notifications wait in killable state (only respond to fatal signals) */
 #define SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV	(1UL << 5)
+/* Indicates that the filter is in form of bpf prog fd */
+#define SECCOMP_FILTER_FLAG_BPF_PROG_FD		(1UL << 6)
 
 /*
  * All BPF programs must return a 32-bit value.
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index c9f6a19f7a4e..3a977e5932a4 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -525,7 +525,10 @@ static inline pid_t seccomp_can_sync_threads(void)
 static inline void seccomp_filter_free(struct seccomp_filter *filter)
 {
 	if (filter) {
-		bpf_prog_destroy(filter->prog);
+		if (filter->prog->type == BPF_PROG_TYPE_SECCOMP)
+			bpf_prog_put(filter->prog);
+		else
+			bpf_prog_destroy(filter->prog);
 		kfree(filter);
 	}
 }
@@ -757,6 +760,33 @@ seccomp_prepare_user_filter(const char __user *user_filter)
 	return sfilter;
 }
 
+/**
+ * seccomp_prepare_filter_from_fd - prepares filter from a user-supplied fd
+ * @ufd: pointer to fd that refers to a seccomp bpf prog.
+ *
+ * Returns filter on success or an ERR_PTR on failure.
+ */
+static struct seccomp_filter *
+seccomp_prepare_filter_from_fd(const char __user *ufd)
+{
+	struct seccomp_filter *sfilter;
+	struct bpf_prog *prog;
+	int fd;
+
+	if (copy_from_user(&fd, ufd, sizeof(fd)))
+		return ERR_PTR(-EFAULT);
+
+	prog = bpf_prog_get_type(fd, BPF_PROG_TYPE_SECCOMP);
+	if (IS_ERR(prog))
+		return ERR_PTR(-EBADF);
+
+	sfilter = seccomp_prepare_filter(prog);
+	if (IS_ERR(sfilter))
+		bpf_prog_put(prog);
+
+	return sfilter;
+}
+
 #ifdef SECCOMP_ARCH_NATIVE
 /**
  * seccomp_is_const_allow - check if filter is constant allow with given data
@@ -1970,7 +2000,10 @@ static long seccomp_set_mode_filter(unsigned int flags,
 		return -EINVAL;
 
 	/* Prepare the new filter before holding any locks. */
-	prepared = seccomp_prepare_user_filter(filter);
+	if (flags & SECCOMP_FILTER_FLAG_BPF_PROG_FD)
+		prepared = seccomp_prepare_filter_from_fd(filter);
+	else
+		prepared = seccomp_prepare_user_filter(filter);
 	if (IS_ERR(prepared))
 		return PTR_ERR(prepared);
 
-- 
2.34.1