Re: [Qemu-devel] Re: [PATCH 07/17] block/vvfat.c: fix warnings with _FORTIFY_SOURCE

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Wed, Jan 20, 2010 at 12:33 PM, Daniel P. Berrange
<berrange@redhat.com> wrote:
> On Wed, Jan 20, 2010 at 08:19:26AM +0200, Kirill A. Shutemov wrote:
>> On Wed, Jan 20, 2010 at 1:56 AM, Juan Quintela <quintela@redhat.com> wrote:
>> > From: Kirill A. Shutemov <kirill@shutemov.name>
>> >
>> > CC    block/vvfat.o
>> > cc1: warnings being treated as errors
>> > block/vvfat.c: In function 'commit_one_file':
>> > block/vvfat.c:2259: error: ignoring return value of 'ftruncate', declared with attribute warn_unused_result
>> > make: *** [block/vvfat.o] Error 1
>> >  CC    block/vvfat.o
>> > In file included from /usr/include/stdio.h:912,
>> >                 from ./qemu-common.h:19,
>> >                 from block/vvfat.c:27:
>> > In function 'snprintf',
>> >    inlined from 'init_directories' at block/vvfat.c:871,
>> >    inlined from 'vvfat_open' at block/vvfat.c:1068:
>> > /usr/include/bits/stdio2.h:65: error: call to __builtin___snprintf_chk will always overflow destination buffer
>> > make: *** [block/vvfat.o] Error 1
>> >
>> > Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
>> > Signed-off-by: Juan Quintela <quintela@redhat.com>
>> > ---
>> >  block/vvfat.c |    9 +++++++--
>> >  1 files changed, 7 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/block/vvfat.c b/block/vvfat.c
>> > index 063f731..df957e5 100644
>> > --- a/block/vvfat.c
>> > +++ b/block/vvfat.c
>> > @@ -868,7 +868,8 @@ static int init_directories(BDRVVVFATState* s,
>> >     {
>> >        direntry_t* entry=array_get_next(&(s->directory));
>> >        entry->attributes=0x28; /* archive | volume label */
>> > -       snprintf((char*)entry->name,11,"QEMU VVFAT");
>> > +       memcpy(entry->name,"QEMU VVF",8);
>> > +       memcpy(entry->extension,"AT ",3);
>> >     }
>>
>> Better to use
>>
>> memcpy(entry->name, "QEMU VVFAT", 11);
>>
>> memcpy() doesn't check bounds.
>
> It doesn't *currently* check bounds.

No. memcpy() will never check bounds. It's totaly different from strcpy,
http://gcc.gnu.org/ml/gcc-patches/2009-06/msg00419.html

> If we want to explicitly
> fill 2 fields at once, then we should redeclare this to have a
> union with one part comprising the entire buffer, thus avoiding
> the need for delibrate buffer overruns.
>
> Regards,
> Daniel
> --
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