linux-kernel - Re: [BUG] kernel: kcov: a possible sleep-in-atomic-context bug in kcov

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <e0305f5c-ae52-c144-fe50-00f3f815ad82@gmail.com>
Date:   Tue, 17 Dec 2019 21:11:27 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Anders Roxell <anders.roxell@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] kernel: kcov: a possible sleep-in-atomic-context bug in
 kcov_ioctl()



On 2019/12/17 21:02, Dmitry Vyukov wrote:
> On Tue, Dec 17, 2019 at 1:56 PM Jia-Ju Bai <baijiaju1990@...il.com> wrote:
>> The kernel may sleep while holding a spinlock.
>> The function call path (from bottom to top) in Linux 4.19 is:
>>
>> kernel/kcov.c, 237:
>>       vfree in kcov_put
>> kernel/kcov.c, 413:
>>       kcov_put in kcov_ioctl_locked
>> kernel/kcov.c, 427:
>>       kcov_ioctl_locked in kcov_ioctl
>> kernel/kcov.c, 426:
>>       spin_lock in kcov_ioctl
>>
>> vfree() can sleep at runtime.
>>
>> I am not sure how to properly fix this possible bug, so I only report it.
>> A possible way is to replace vfree() with kfree(), and replace related
>> calls to vmalloc() with kmalloc().
>>
>> This bug is found by a static analysis tool STCheck written by myself.
> Hi Jia-Ju,
>
> Are you sure kcov_ioctl_locked can really release the descriptor? It
> happens in the context of ioctl, which means there is an open
> reference for the file descriptor. So ioctl should not do vfree I
> would assume.

Thanks for the reply :)
I am not sure, because I am not familiar with kcov.
But looking at the code, if the reference count of kcov is 1, vfree() 
could be called.


Best wishes,
Jia-Ju Bai