2023-11-22 05:29:06

by Yonghong Song

Subject: Re: [PATCH net] bpf: test_run: fix WARNING in format_decode

On 11/21/23 7:50 PM, Edward Adam Davis wrote:
> Confirm that skb->len is not 0 to ensure that skb length is valid.
>
> Fixes: 114039b34201 ("bpf: Move skb->len == 0 checks into __bpf_redirect")
> Reported-by: [email protected]
> Signed-off-by: Edward Adam Davis <[email protected]>

Stan, Could you take a look at this patch?


> ---
> net/bpf/test_run.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index c9fdcc5cdce1..78258a822a5c 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -845,6 +845,9 @@ static int convert___skb_to_skb(struct sk_buff *skb, struct __sk_buff *__skb)
> {
> struct qdisc_skb_cb *cb = (struct qdisc_skb_cb *)skb->cb;
>
> + if (!skb->len)
> + return -EINVAL;
> +
> if (!__skb)
> return 0;
>

2023-11-27 14:18:11

by Daniel Borkmann

Subject: Re: [PATCH net] bpf: test_run: fix WARNING in format_decode

On 11/22/23 6:28 AM, Yonghong Song wrote:
> On 11/21/23 7:50 PM, Edward Adam Davis wrote:
>> Confirm that skb->len is not 0 to ensure that skb length is valid.
>>
>> Fixes: 114039b34201 ("bpf: Move skb->len == 0 checks into __bpf_redirect")
>> Reported-by: [email protected]
>> Signed-off-by: Edward Adam Davis <[email protected]>
>
> Stan, Could you take a look at this patch?

I think this only papers over the bug.. also BPF selftests seem to break
with this change.

Looking again at the syzkaller trace :

[...]
Please remove unsupported %\0 in format string
WARNING: CPU: 0 PID: 5068 at lib/vsprintf.c:2675 format_decode+0xa03/0xba0 lib/vsprintf.c:2675
[...]

We need to fix bpf_bprintf_prepare() instead to reject invalid fmts such
as %0 and similar.

>>   net/bpf/test_run.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
>> index c9fdcc5cdce1..78258a822a5c 100644
>> --- a/net/bpf/test_run.c
>> +++ b/net/bpf/test_run.c
>> @@ -845,6 +845,9 @@ static int convert___skb_to_skb(struct sk_buff *skb, struct __sk_buff *__skb)
>>   {
>>       struct qdisc_skb_cb *cb = (struct qdisc_skb_cb *)skb->cb;
>> +    if (!skb->len)
>> +        return -EINVAL;
>> +
>>       if (!__skb)
>>           return 0;