[U-Boot] [PATCH] LZMA: Avoid free on null pointer.

[Luigi Mantellini]

On Mon, Dec 6, 2010 at 8:15 AM, Mike Frysinger <vapier at gentoo.org> wrote:
> On Sunday, December 05, 2010 04:18:44 Luigi 'Comio' Mantellini wrote:
>> On structure Initialization, LZMA code tries to free the dictionary
>> and probs buffers, also when these are null pointers. Add some
>> check in order to prevent the free on null pointers.
>
> your patch only checks p->probs, not any dictionary buffer.  if you follow the
> code path:
>
> ...
> void LzmaDec_FreeProbs(CLzmaDec *p, ISzAlloc *alloc)
> {
>  alloc->Free(alloc, p->probs);
>  p->probs = 0;
> }
> ...
>    g_Alloc.Free = SzFree;
> ...
> static void SzFree(void *p, void *address) { p = p; free(address); }
> ...
>
> this only ends up doing free(p->probs) which is free(NULL) which isnt a bug.
>

In general I prefer avoid to free a null pointer, and I consider a
free on a not-malloc-eted pointer a bug. The submitted patch check the
pointers (p->probs and p->dict) only at init time. This is sufficient
to avoid the free(NULL). The other *Free(*) calls all called on
pointers that are surely not null.

The second way should be to add the null check into the FreeProbs and
FreeDict functions.

best regards,

luigi

> so you're going to need to provide some more details.
> -mike
>
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-- 
Luigi 'Comio' Mantellini
R&D - Software
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