[PATCH v2 bpf-next] selftest: bpf: Remove mssind boundary check in test_tcp_custom_syncookie.c.

[PATCH v2 bpf-next] selftest: bpf: Remove mssind boundary check in test_tcp_custom_syncookie.c.

[Kuniyuki Iwashima]

Smatch reported a possible off-by-one in tcp_validate_cookie().

However, it's false positive because the possible range of mssind is
limited from 0 to 3 by the preceding calculation.

  mssind = (cookie & (3 << 6)) >> 6;

Now, the verifier does not complain without the boundary check.
Let's remove the checks.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/bpf/6ae12487-d3f1-488b-9514-af0dac96608f@stanley.mountain/
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 .../selftests/bpf/progs/test_tcp_custom_syncookie.c   | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
index 44ee0d037f95..eb5cca1fce16 100644
--- a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
+++ b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
@@ -486,17 +486,10 @@ static int tcp_validate_cookie(struct tcp_syncookie *ctx)
 		goto err;
 
 	mssind = (cookie & (3 << 6)) >> 6;
-	if (ctx->ipv4) {
-		if (mssind > ARRAY_SIZE(msstab4))
-			goto err;
-
+	if (ctx->ipv4)
 		ctx->attrs.mss = msstab4[mssind];
-	} else {
-		if (mssind > ARRAY_SIZE(msstab6))
-			goto err;
-
+	else
 		ctx->attrs.mss = msstab6[mssind];
-	}
 
 	ctx->attrs.snd_wscale = cookie & BPF_SYNCOOKIE_WSCALE_MASK;
 	ctx->attrs.rcv_wscale = ctx->attrs.snd_wscale;
-- 
2.30.2

Re: [PATCH v2 bpf-next] selftest: bpf: Remove mssind boundary check in test_tcp_custom_syncookie.c.

[Yonghong Song]

On 8/20/24 6:34 PM, Kuniyuki Iwashima wrote:
> Smatch reported a possible off-by-one in tcp_validate_cookie().
>
> However, it's false positive because the possible range of mssind is
> limited from 0 to 3 by the preceding calculation.
>
>    mssind = (cookie & (3 << 6)) >> 6;
>
> Now, the verifier does not complain without the boundary check.
> Let's remove the checks.
>
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Closes: https://lore.kernel.org/bpf/6ae12487-d3f1-488b-9514-af0dac96608f@stanley.mountain/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>

Re: [PATCH v2 bpf-next] selftest: bpf: Remove mssind boundary check in test_tcp_custom_syncookie.c.

[Martin KaFai Lau]

On 8/21/24 7:54 AM, Yonghong Song wrote:
> 
> On 8/20/24 6:34 PM, Kuniyuki Iwashima wrote:
>> Smatch reported a possible off-by-one in tcp_validate_cookie().
>>
>> However, it's false positive because the possible range of mssind is
>> limited from 0 to 3 by the preceding calculation.
>>
>>    mssind = (cookie & (3 << 6)) >> 6;
>>
>> Now, the verifier does not complain without the boundary check.
>> Let's remove the checks.
>>
>> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
>> Closes: https://lore.kernel.org/bpf/6ae12487-d3f1-488b-9514- 
>> af0dac96608f@stanley.mountain/
>> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> Acked-by: Yonghong Song <yonghong.song@linux.dev>

Applied to bpf-next/net. Thanks.