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Re: [Qemu-devel] [PATCH v2 0/3] Fix strncpy() warnings for GCC8 new -Wst

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v2 0/3] Fix strncpy() warnings for GCC8 new -Wstringop-truncation
Date: Tue, 18 Dec 2018 18:38:09 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1

On 18/12/18 18:17, Michael S. Tsirkin wrote:
> On Tue, Dec 18, 2018 at 06:12:05PM +0100, Paolo Bonzini wrote:
>> On 18/12/18 17:55, Philippe Mathieu-Daudé wrote:
>>>> strpadcpy will instead just silence the warning.
>>> migration/global_state.c:109:15: error: 'strlen' argument 1 declared
>>> attribute 'nonstring' [-Werror=stringop-overflow=]
>>>      s->size = strlen((char *)s->runstate) + 1;
>>>                ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> GCC won... It is true this strlen() is buggy, indeed s->runstate might
>>> be not NUL-terminated.
>> No, runstate is declared as an array of 100 bytes, which are more than
>> enough.  It's ugly code but not buggy.
>> Paolo
> Yes ... but it is loaded using
>         VMSTATE_BUFFER(runstate, GlobalState),
> and parsed using qapi_enum_parse which does not get
> the buffer length.
> So unless we are lucky there's a buffer overrun
> on a remote/file input here.
> Seems buggy to me - what am I missing?

Yup.   I think we're lucky twice though.  First, the state field stops
the runaway qapi_enum_parse.  Second, in any case worst case it's a segv
on migration.  This is a bug but not a CVE.


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