Re: [Qemu-devel] [PATCH] use qemu_malloc and friends consistently

[malc <av1474@comtv.ru>]

On Fri, 29 May 2009, Kevin Wolf wrote:

> malc schrieb:
> > On Fri, 29 May 2009, Kevin Wolf wrote:
> > 
> >> malc schrieb:
> >>> On Fri, 29 May 2009, Kevin Wolf wrote:
> >>>

[..snip..]

> > 
> > Because of oom_check in qemu_malloc.
> 
> Ok, you're right there, of course. This is a bug in qemu_malloc and the
> reason why we even discussed changing the check in qemu_malloc.
> 
> But this is not qcow2's fault, so the fix should really be local to
> qemu_malloc like it already was for qemu_realloc.

I'll rehash it one last time:

a. Original code in qcow2 did:
   p = qemu_malloc(nb_snapshots*sizeof_snapshot);
   if (!p) return_failure;

I.e. incorrect, when stuff==0 and platform==SYSV_derivative that picked
return NULL on size 0 among the IDB choices that standard provides.

b. Code after oom_check went in
   p = qemu_malloc(nb_snapshots*sizeof_snapshot);
   /* check gone */
   for (i = 0; i < nb_snapshots; i++)

I.e. incorrect, when stuff==0 and platform ... since oom_check would
kill it.

So the code in qcow2 was _never_ correct, not a single time. The fact
that it wouldn't crash since it doesn't dereference returned pointer
was/is irrelevant.

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