netdev - [PATCH] bpf: Fix off-by-one in tail call count limiting

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Date:   Wed, 28 Jul 2021 18:47:41 +0200
From:   Johan Almbladh <johan.almbladh@...finetworks.com>
To:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org
Cc:     kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org,
        Tony.Ambardar@...il.com, netdev@...r.kernel.org,
        bpf@...r.kernel.org,
        Johan Almbladh <johan.almbladh@...finetworks.com>
Subject: [PATCH] bpf: Fix off-by-one in tail call count limiting

Before, the interpreter allowed up to MAX_TAIL_CALL_CNT + 1 tail calls.
Now precisely MAX_TAIL_CALL_CNT is allowed, which is in line with the
behavior of the x86 JITs.

Signed-off-by: Johan Almbladh <johan.almbladh@...finetworks.com>
---
 kernel/bpf/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 9b1577498373..67682b3afc84 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1559,7 +1559,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
 
 		if (unlikely(index >= array->map.max_entries))
 			goto out;
-		if (unlikely(tail_call_cnt > MAX_TAIL_CALL_CNT))
+		if (unlikely(tail_call_cnt >= MAX_TAIL_CALL_CNT))
 			goto out;
 
 		tail_call_cnt++;
-- 
2.25.1