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Message-ID: <0a392ae2-9fd0-4a13-a4b1-5454b17701bb@schaufler-ca.com>
Date: Mon, 18 Dec 2023 09:54:13 -0800
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Subject: Re: [PATCH] SELinux: Introduce security_file_ioctl_compat hook
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To: Stephen Smalley <stephen.smalley.work@gmail.com>
Cc: Alfred Piccioni <alpic@google.com>, Paul Moore <paul@paul-moore.com>,
 Eric Paris <eparis@parisplace.org>, stable@vger.kernel.org,
 selinux@vger.kernel.org, linux-kernel@vger.kernel.org,
 Casey Schaufler <casey@schaufler-ca.com>
References: <20231218141645.2548743-1-alpic@google.com>
 <6dce3020-14f0-471b-9b6a-c9dc761cfa19@schaufler-ca.com>
 <CAEjxPJ4tZAvch50i7Ve_7dPYUzCXK8ckDtmhwq81vjCf7pweQw@mail.gmail.com>
From: Casey Schaufler <casey@schaufler-ca.com>
In-Reply-To: <CAEjxPJ4tZAvch50i7Ve_7dPYUzCXK8ckDtmhwq81vjCf7pweQw@mail.gmail.com>
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On 12/18/2023 9:36 AM, Stephen Smalley wrote:
> On Mon, Dec 18, 2023 at 12:11 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
>> On 12/18/2023 6:16 AM, Alfred Piccioni wrote:
>>
>>> Some ioctl commands do not require ioctl permission, but are routed to
>>> other permissions such as FILE_GETATTR or FILE_SETATTR. This routing is
>>> done by comparing the ioctl cmd to a set of 64-bit flags (FS_IOC_*).
>>>
>>> However, if a 32-bit process is running on a 64-bit kernel, it emits
>>> 32-bit flags (FS_IOC32_*) for certain ioctl operations. These flags are
>>> being checked erroneously, which leads to these ioctl operations being
>>> routed to the ioctl permission, rather than the correct file
>>> permissions.
>>>
>>> This was also noted in a RED-PEN finding from a while back -
>>> "/* RED-PEN how should LSM module know it's handling 32bit? */".
>>>
>>> This patch introduces a new hook, security_file_ioctl_compat, that is
>>> called from the compat ioctl syscal. All current LSMs have been changed
>>> to support this hook.
>>>
>>> Reviewing the three places where we are currently using
>>> security_file_ioctl, it appears that only SELinux needs a dedicated
>>> compat change; TOMOYO and SMACK appear to be functional without any
>>> change.
>>>
>>> Fixes: 0b24dcb7f2f7 ("Revert "selinux: simplify ioctl checking"")
>>> Signed-off-by: Alfred Piccioni <alpic@google.com>
>>> Cc: stable@vger.kernel.org
>> This *really* needs to go the the LSM email list:
>>         linux-security-module@vger.kernel.org
> Yep, pointed that out a little earlier in this thread.
>
>>> ---
>>> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
>>> index ac962c4cb44b..626aa8cf930d 100644
>>> --- a/include/linux/lsm_hook_defs.h
>>> +++ b/include/linux/lsm_hook_defs.h
>>> @@ -171,6 +171,8 @@ LSM_HOOK(int, 0, file_alloc_security, struct file *file)
>>>  LSM_HOOK(void, LSM_RET_VOID, file_free_security, struct file *file)
>>>  LSM_HOOK(int, 0, file_ioctl, struct file *file, unsigned int cmd,
>>>        unsigned long arg)
>>> +LSM_HOOK(int, 0, file_ioctl_compat, struct file *file, unsigned int cmd,
>>> +      unsigned long arg)
>> Please add a flags parameter to file_ioctl() rather than a new hook.
> Paul told him the opposite earlier.

Sigh. Paul's wrong, but as he's the maintainer I shan't push further.