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Re: [Qemu-devel] [PATCH] nbd: Initialize reply on failure
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [Qemu-devel] [PATCH] nbd: Initialize reply on failure |
Date: |
Fri, 19 Jul 2019 19:17:35 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 |
On 7/19/19 7:15 PM, Eric Blake wrote:
> On 7/19/19 10:03 AM, Eric Blake wrote:
>> We've had two separate reports of a caller running into use of
>> uninitialized data if s->quit is set (one detected by gcc -O3, another
>> by valgrind), due to checking 'nbd_reply_is_simple(reply) || s->quit'
>> in the wrong order. Rather than chasing down which callers need to
>> pre-initialize reply, it's easier to guarantee that reply will always
>> be set by nbd_co_receive_one_chunk() even on failure.
>>
>> Reported-by: Thomas Huth <address@hidden>
>> Reported-by: Andrey Shinkevich <address@hidden>
>> Signed-off-by: Eric Blake <address@hidden>
>> ---
>>
>
> Blech. Needs a v2. Expanding context:
>
>
>> +++ b/block/nbd.c
>> @@ -640,6 +640,7 @@ static coroutine_fn int nbd_co_receive_one_chunk(
>> request_ret, qiov, payload, errp);
>>
>> if (ret < 0) {
>> + memset(reply, 0, sizeof *reply);
>> s->quit = true;
>> } else {
>> /* For assert at loop start in nbd_connection_entry */
> if (reply) {
> *reply = s->reply;
> }
>
> either callers can pass in reply==NULL (in which case the memset()
> dereferences NULL, oops), or always pass in non-NULL reply (in which
Oh good catch...
> case the null check is dead code).
>