[PATCH AUTOSEL 5.14 101/252] bpf: Fix off-by-one in tail call count limiting

[Sasha Levin <sashal@kernel.org>]

From: Johan Almbladh <johan.almbladh@anyfinetworks.com>

[ Upstream commit b61a28cf11d61f512172e673b8f8c4a6c789b425 ]

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@anyfinetworks.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210728164741.350370-1-johan.almbladh@anyfinetworks.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 0a28a8095d3e..82af6279992d 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1564,7 +1564,7 @@ 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++;
-- 
2.30.2