Re: [PATCH] Fix Python crash on getprop deallocation

[David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>]

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On Fri, Dec 24, 2021 at 11:28:12AM +0100, Luca Weiss wrote:
> Fatal Python error: none_dealloc: deallocating None
> Python runtime state: finalizing (tstate=0x000055c9bac70920)
> 
> Current thread 0x00007fbe34e47740 (most recent call first):
>   <no Python frame>
> Aborted (core dumped)
> 
> This is caused by a missing Py_INCREF on the returned Py_None, as
> demonstrated e.g. in https://github.com/mythosil/swig-python-incref or
> described at https://edcjones.tripod.com/refcount.html ("Remember to
> INCREF Py_None!")
> 
> A PoC for triggering this crash is uploaded to
> https://github.com/z3ntu/pylibfdt-crash .
> With this patch applied to pylibfdt the crash does not happen.

Any chance you could rework your testcase into the libfdt testsuite
(make check)?

> Signed-off-by: Luca Weiss <luca-IfPCFPJWly+lVyrhU4qvOw@public.gmane.org>
> ---
> Unrelated but I've noticed that in this file the indentation is quite
> mixed between spaces and tabs. This patch tries to keep to the style in
> the lines around.
> 
>  pylibfdt/libfdt.i | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/pylibfdt/libfdt.i b/pylibfdt/libfdt.i
> index 075ef70..9ccc57b 100644
> --- a/pylibfdt/libfdt.i
> +++ b/pylibfdt/libfdt.i
> @@ -1040,14 +1040,16 @@ typedef uint32_t fdt32_t;
>  
>  /* typemap used for fdt_getprop() */
>  %typemap(out) (const void *) {
> -	if (!$1)
> +	if (!$1) {
>  		$result = Py_None;
> -	else
> +		Py_INCREF($result);
> +	} else {
>          %#if PY_VERSION_HEX >= 0x03000000
>              $result = Py_BuildValue("y#", $1, (Py_ssize_t)*arg4);
>          %#else
>              $result = Py_BuildValue("s#", $1, (Py_ssize_t)*arg4);
>          %#endif
> +    }
>  }
>  
>  /* typemap used for fdt_setprop() */

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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