[PATCH AUTOSEL 5.10 071/176] bpf: Fix off-by-one in tail call count limiting

Sasha Levin
2021-09-09T12:42:19Z

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 d12efb2550d3..f25b23fddbee 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1565,7 +1565,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)

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