linux-kernel - [PATCH bpf-next] bpf: Fix potential array overflow in bpf_trampoline_get

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Date:   Sat, 30 Apr 2022 21:08:03 +0800
From:   Yuntao Wang <ytcoode@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yuntao Wang <ytcoode@...il.com>
Subject: [PATCH bpf-next] bpf: Fix potential array overflow in bpf_trampoline_get_progs()

The cnt value in the 'cnt >= BPF_MAX_TRAMP_PROGS' check does not
include BPF_TRAMP_MODIFY_RETURN bpf programs, so the number of
the attached BPF_TRAMP_MODIFY_RETURN bpf programs in a trampoline
can exceed BPF_MAX_TRAMP_PROGS.

When this happens, the assignment '*progs++ = aux->prog' in
bpf_trampoline_get_progs() will cause progs array overflow as the
progs field in the bpf_tramp_progs struct can only hold at most
BPF_MAX_TRAMP_PROGS bpf programs.

Fixes: 88fd9e5352fe ("bpf: Refactor trampoline update code")
Signed-off-by: Yuntao Wang <ytcoode@...il.com>
---
 kernel/bpf/trampoline.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index ada97751ae1b..5d8bfb5ef239 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -411,7 +411,7 @@ int bpf_trampoline_link_prog(struct bpf_prog *prog, struct bpf_trampoline *tr)
 {
 	enum bpf_tramp_prog_type kind;
 	int err = 0;
-	int cnt;
+	int cnt = 0, i;
 
 	kind = bpf_attach_type_to_tramp(prog);
 	mutex_lock(&tr->mutex);
@@ -422,7 +422,10 @@ int bpf_trampoline_link_prog(struct bpf_prog *prog, struct bpf_trampoline *tr)
 		err = -EBUSY;
 		goto out;
 	}
-	cnt = tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT];
+
+	for (i = 0; i < BPF_TRAMP_MAX; i++)
+		cnt += tr->progs_cnt[i];
+
 	if (kind == BPF_TRAMP_REPLACE) {
 		/* Cannot attach extension if fentry/fexit are in use. */
 		if (cnt) {
@@ -500,16 +503,19 @@ struct bpf_trampoline *bpf_trampoline_get(u64 key,
 
 void bpf_trampoline_put(struct bpf_trampoline *tr)
 {
+	int i;
+
 	if (!tr)
 		return;
 	mutex_lock(&trampoline_mutex);
 	if (!refcount_dec_and_test(&tr->refcnt))
 		goto out;
 	WARN_ON_ONCE(mutex_is_locked(&tr->mutex));
-	if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FENTRY])))
-		goto out;
-	if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FEXIT])))
-		goto out;
+
+	for (i = 0; i < BPF_TRAMP_MAX; i++)
+		if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[i])))
+			goto out;
+
 	/* This code will be executed even when the last bpf_tramp_image
 	 * is alive. All progs are detached from the trampoline and the
 	 * trampoline image is patched with jmp into epilogue to skip
-- 
2.36.0