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

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

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@...verde.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