Re: [PATCH] tcp_vu: Fix assert/error-check order in tcp_vu_sock_recv()

[Laurent Vivier <lvivier@redhat.com>]

On 11/10/26 10:29, Stefano Brivio wrote:
> [Cc: Johannes, Laurent]
> 
> Thanks for the patch and the explanation, but shouldn't this be:
> 
> On Mon,  9 Nov 2026 17:13:42 -0500
> Jon Maloy <jmaloy@redhat.com> wrote:
> 
> From: Johannes Bartunek <contact@jbartunek.de>
> 
> and:
> 
>> iov_tail_clone() returns a ssize_t. However, the assert comparing
>> it against (ARRAY_SIZE(iov_msg) - j), which yields size_t, comes
>> before the negative-value check. Hence, when iov_tail_clone() fails
>> and returns -1, the signed-to-unsigned promotion turns -1 into
>> SIZE_MAX, and causes the assert to fire.
>>
>> We fix this by moving the error check before the assert, while casting
>> the counter and the index inside the assert to size_t.
> 
> Reported-by: Johannes Bartunek <contact@jbartunek.de>
> Suggested-by: Laurent Vivier <lvivier@redhat.com>

Not exactly...

> 
> ?
> 
>> Signed-off-by: Jon Maloy <jmaloy@redhat.com>
>> ---
>>   tcp_vu.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tcp_vu.c b/tcp_vu.c
>> index 868a35b9..c052d8e2 100644
>> --- a/tcp_vu.c
>> +++ b/tcp_vu.c
>> @@ -291,9 +291,9 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq,
>>   
>>   		cnt = iov_tail_clone(&iov_msg[j], ARRAY_SIZE(iov_msg) - j,
>>   				     &data);
>> -		assert(cnt < ARRAY_SIZE(iov_msg) - j);
>>   		if (cnt < 0)
>>   			die("Missing entries in iov_msg");
>> +		assert((size_t)cnt < ARRAY_SIZE(iov_msg) - (size_t)j);

The real fix is:

assert((size_t)cnt <= ARRAY_SIZE(iov_msg) - (size_t)j);

>>   
>>   		j += cnt;
>>   	}
> 

Thanks,
Laurent