bpf: sockmap: Require attach_bpf_fd when detaching a program

The sockmap code currently ignores the value of attach_bpf_fd when
detaching a program. This is contrary to the usual behaviour of
checking that attach_bpf_fd represents the currently attached
program.

Ensure that attach_bpf_fd is indeed the currently attached
program. It turns out that all sockmap selftests already do this,
which indicates that this is unlikely to cause breakage.

Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200629095630.7933-5-lmb@cloudflare.com

1 files changed, 13 insertions, 0 deletions

diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index 08674cd14d5a..1e9ed840b9fc 100644
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -430,6 +430,19 @@ static inline void psock_set_prog(struct bpf_prog **pprog,
 		bpf_prog_put(prog);
 }
 
+static inline int psock_replace_prog(struct bpf_prog **pprog,
+				     struct bpf_prog *prog,
+				     struct bpf_prog *old)
+{
+	if (cmpxchg(pprog, old, prog) != old)
+		return -ENOENT;
+
+	if (old)
+		bpf_prog_put(old);
+
+	return 0;
+}
+
 static inline void psock_progs_drop(struct sk_psock_progs *progs)
 {
 	psock_set_prog(&progs->msg_parser, NULL);