[PATCH bpf-next] bpf: prevent leak of lsm program after failed attach

From: Milan Landaverde <milan@mdaverde.com>
To: bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	John Fastabend <john.fastabend@gmail.com>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <martin.lau@linux.dev>,
	Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
	KP Singh <kpsingh@kernel.org>,
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
	Jiri Olsa <jolsa@kernel.org>,
	linux-kernel@vger.kernel.org,
	Milan Landaverde <milan@mdaverde.com>
Subject: [PATCH bpf-next] bpf: prevent leak of lsm program after failed attach
Date: Tue, 13 Dec 2022 12:57:14 -0500	[thread overview]
Message-ID: <20221213175714.31963-1-milan@mdaverde.com> (raw)

In [0], we added the ability to bpf_prog_attach LSM programs to cgroups,
but in our validation to make sure the prog is meant to be attached to
BPF_LSM_CGROUP, we return too early if the check fails. This results in
lack of decrementing prog's refcnt (through bpf_prog_put)
leaving the LSM program alive past the point of the expected lifecycle.
This fix allows for the decrement to take place.

[0] https://lore.kernel.org/all/20220628174314.1216643-4-sdf@google.com/

Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
Signed-off-by: Milan Landaverde <milan@mdaverde.com>
---
 kernel/bpf/syscall.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 35972afb6850..64131f88c553 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3518,9 +3518,9 @@ static int bpf_prog_attach(const union bpf_attr *attr)
 	case BPF_PROG_TYPE_LSM:
 		if (ptype == BPF_PROG_TYPE_LSM &&
 		    prog->expected_attach_type != BPF_LSM_CGROUP)
-			return -EINVAL;
-
-		ret = cgroup_bpf_prog_attach(attr, ptype, prog);
+			ret = -EINVAL;
+		else
+			ret = cgroup_bpf_prog_attach(attr, ptype, prog);
 		break;
 	default:
 		ret = -EINVAL;
-- 
2.34.1

