linux-kernel - Re: [PATCH] efi/esrt: Fix reference count leak in esre_create_sysfs

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Date:   Mon, 15 Jun 2020 11:48:53 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Qiushi Wu <wu000273@....edu>
Cc:     Kangjie Lu <kjlu@....edu>, Peter Jones <pjones@...hat.com>,
        Matt Fleming <matt.fleming@...el.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] efi/esrt: Fix reference count leak in esre_create_sysfs_entry.

On Sat, 30 May 2020 at 06:23, Qiushi Wu <wu000273@....edu> wrote:
>
> Thanks for your reply!
>  > Why are you removing this kfree() call?
>
> Because  kobject_put(&entry->kobj) will call kobject_release(), which will call kobject_cleanup(), which will dynamically call get_ktype(kobj)->release(kobj); .
> In this case, the "release" function is defined as:
> static struct kobj_type esre1_ktype = {
> .release = esre_release.
> ...
> };
>
> and esre_release() is defined as :
> static void esre_release(struct kobject *kobj) {
>            struct esre_entry *entry = to_entry(kobj);
>            list_del(&entry->list);
>            kfree(entry);
> }
>
> In this case, if we call both kobject_put() and kfree(), a double-free will be introduced.
>

Thanks for the explanation

Queued in efi/urgent.

> On Fri, May 29, 2020 at 12:00 PM Ard Biesheuvel <ardb@...nel.org> wrote:
>>
>> On Thu, 28 May 2020 at 20:38, <wu000273@....edu> wrote:
>> >
>> > From: Qiushi Wu <wu000273@....edu>
>> >
>> > kobject_init_and_add() takes reference even when it fails.
>> > If this function returns an error, kobject_put() must be called to
>> > properly clean up the memory associated with the object. Previous
>> > commit "b8eb718348b8" fixed a similar problem.
>> >
>> > Fixes: 0bb549052d33 ("efi: Add esrt support")
>> > Signed-off-by: Qiushi Wu <wu000273@....edu>
>> > ---
>> >  drivers/firmware/efi/esrt.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/firmware/efi/esrt.c b/drivers/firmware/efi/esrt.c
>> > index e3d692696583..d5915272141f 100644
>> > --- a/drivers/firmware/efi/esrt.c
>> > +++ b/drivers/firmware/efi/esrt.c
>> > @@ -181,7 +181,7 @@ static int esre_create_sysfs_entry(void *esre, int entry_num)
>> >                 rc = kobject_init_and_add(&entry->kobj, &esre1_ktype, NULL,
>> >                                           "entry%d", entry_num);
>> >                 if (rc) {
>> > -                       kfree(entry);
>>
>> Why are you removing this kfree() call?
>>
>> > +                       kobject_put(&entry->kobj);
>> >                         return rc;
>> >                 }
>> >         }
>> > --
>> > 2.17.1
>> >