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

Subsystems: bpf [core], bpf [general] (safe dynamic programs and tools), the rest

STALE1784d REVIEWED: 1 (0M)

1 review trailer.

2 messages, 2 authors, 2021-09-14 · open the first message on its own page

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

From: Sasha Levin <sashal@kernel.org>
Date: 2021-09-09 11:49:27

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 <redacted>
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

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

From: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Date: 2021-09-14 04:09:14

Sasha,

This patch should not be applied to any of the stable kernels. It was
reverted in f9dabe016b63 ("bpf: Undo off-by-one in interpreter tail
call count limit").

I don't think it will pass the CI selftests so maybe it wouldn't be
applied anyway, but nevertheless I want to inform you about it.

Johan

On Thu, Sep 9, 2021 at 1:43 PM Sasha Levin [off-list ref] wrote:

quoted hunk

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 <redacted>
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

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