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Re: [Qemu-devel] [PATCH v2] bt: use size_t type for length parameters in

From: Hugo Lefeuvre
Subject: Re: [Qemu-devel] [PATCH v2] bt: use size_t type for length parameters instead of int
Date: Tue, 29 Jan 2019 14:13:11 +0100
User-agent: Mutt/1.10.1 (2018-07-13)

Hi Philippe,

> I have been assigned to fix this issue, but rather fixing locally this
> BT device, fix the pattern on all devices.
> I'll post the series during the week and Cc you (and eventually the
> Debian LTS list when it gets merged). The series obsoletes this patch,
> so the plan is to not apply it.

Thanks ! I will wait for your patch then.

> > Any reason why assert() calls are used here ?
> > 
> > These checks should always be executed, but they won't if user compiles
> > without asserts. Also, AFAIK any assert failure will stop the qemu host
> > process which is not what we want in this case.
> There was a discussion about this, and the outcome is QEMU does not
> support building without assertions. See this commit:
> https://git.qemu.org/?p=qemu.git;a=blobdiff;f=include/qemu/osdep.h;h=9966638;hp=6855b94;hb=262a69f42;hpb=825bfa005

Makes sense. But I'm still sceptical about assert() being used here.

For example:

    @@ -113,6 +113,7 @@ static void vhci_host_send(void *opaque,
         static uint8_t buf[4096];
         buf[0] = type;
    +    assert(len < sizeof(buf));
         memcpy(buf + 1, data, len);
         while (write(s->fd, buf, len + 1) < 0)

From my understanding assert() calls are supposed to be a way to verify
code assumptions at runtime. assert failures are always bugs, so they
terminate the process.

If len is passed by guest systems, an excessive value should not be
considered a bug but invalid user passed input, that is normal behaviour,
right? In this case I expect qemu to simply reject the input instead of
triggering an assert failure and terminating.


                Hugo Lefeuvre (hle)    |    www.owl.eu.com
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