[net] bpf: test_run: fix WARNING in format_decode

Commit Message

Edward Adam Davis Nov. 22, 2023, 12:50 a.m. UTC

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: [e-mail]
Signed-off-by: Edward Adam Davis <[e-mail]>
---
 net/bpf/test_run.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

Yonghong Song Nov. 22, 2023, 5:28 a.m. UTC | #1

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: [e-mail]
> Signed-off-by: Edward Adam Davis <[e-mail]>

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;
>

Daniel Borkmann Nov. 27, 2023, 2:10 p.m. UTC | #2

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: [e-mail]
>> Signed-off-by: Edward Adam Davis <[e-mail]>
> 
> 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;

Patch

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;