[PATCH] fsi: Aspeed: Fix a potential double free
christophe.jaillet at wanadoo.fr
Fri Jan 7 05:35:56 AEDT 2022
Le 06/01/2022 à 18:25, Guenter Roeck a écrit :
> On 1/6/22 12:14 AM, Dan Carpenter wrote:
>> On Mon, Dec 27, 2021 at 07:29:07AM +0100, Greg KH wrote:
>>> On Sun, Dec 26, 2021 at 05:56:02PM +0100, Christophe JAILLET wrote:
>>>> 'aspeed' is a devm_alloc'ed, so there is no need to free it
>>>> explicitly or
>>>> there will be a double free().
>>> A struct device can never be devm_alloced for obvious reasons. Perhaps
>>> that is the real problem here?
>> I don't understand how "aspeed" is a struct device.
> -static void aspeed_master_release(struct device *dev)
> - struct fsi_master_aspeed *aspeed =
> - to_fsi_master_aspeed(dev_to_fsi_master(dev));
> - kfree(aspeed);
> So "dev" is embedded in struct fsi_master, and struct fsi_master is
> in struct fsi_master_aspeed. Since "struct device" is embedded, the data
> structure embedding it must be released with the release function, as is
> here. The problem is indeed that the data structure is allocated with
> devm_kzalloc(), which as Greg points out must not be devm_ allocated
> (because its lifetime does not match the lifetime of devm_ allocated
Thanks a lot for the detailed explanation.
Crystal clear for me now.
Do you want me to send a patch to remove the devm_ or will you?
>> I've been working on understanding device managed memory recently for
>> Smatch. It's really complicated. There are a bunch of rules/heuristics
>> that I'm slowly creating to generate new warnings but I'm a long way
>> from understanding it well myself.
> A data structure embedding struct device must not be devm_ allocated,
> and it must be released with the release callback. Maybe there is
> a means to flag that somehow ?
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