[PATCH v2 2/4] net: filter: add sk_attach_filter_kern() function

[Rongguang Wei <clementwei90@163.com>]

From: Rongguang Wei <weirongguang@kylinos.cn>

sk_attach_filter() copies the program from user space and sk_attach_bpf()
takes it from a user file descriptor, so a program that the kernel keeps in
memory cannot be installed again later.

sk_attach_filter_kern() builds the program from a sock_fprog_kern, so no
user buffer is read, and attaches it like sk_attach_filter(). The caller
must hold the socket lock. Failing the attach releases it; so does the
socket when the filter is replaced, detached or the socket goes away.

Signed-off-by: Rongguang Wei <weirongguang@kylinos.cn>
---
 include/linux/filter.h |  1 +
 net/core/filter.c      | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 39decde7fc73..0de5a738fb26 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1218,6 +1218,7 @@ int bpf_prog_create_from_user(struct bpf_prog **pfp, struct sock_fprog *fprog,
 void bpf_prog_destroy(struct bpf_prog *fp);
 
 int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk);
+int sk_attach_filter_kern(struct sock_fprog_kern *fprog, struct sock *sk);
 int sk_attach_bpf(u32 ufd, struct sock *sk);
 int sk_reuseport_attach_filter(struct sock_fprog *fprog, struct sock *sk);
 int sk_reuseport_attach_bpf(u32 ufd, struct sock *sk);
diff --git a/net/core/filter.c b/net/core/filter.c
index 70dc621672f2..64d6505a4ef2 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1567,6 +1567,28 @@ int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 }
 EXPORT_SYMBOL_GPL(sk_attach_filter);
 
+int sk_attach_filter_kern(struct sock_fprog_kern *fprog, struct sock *sk)
+{
+	struct bpf_prog *prog;
+	int err;
+
+	if (sock_flag(sk, SOCK_FILTER_LOCKED))
+		return -EPERM;
+
+	err = bpf_prog_create(&prog, fprog);
+	if (err)
+		return err;
+
+	err = __sk_attach_prog(prog, sk);
+	if (err < 0) {
+		__bpf_prog_release(prog);
+		return err;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(sk_attach_filter_kern);
+
 int sk_reuseport_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 {
 	struct bpf_prog *prog = __get_filter(fprog, sk);
-- 
2.25.1


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