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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Mon, 2 Jul 2018 14:15:39 +0200
Message-ID: <CACT4Y+YanGz1DNav=cxDj1ianjmAKnA4s7wuhhop2RzrOsKAUQ@mail.gmail.com>
Subject: Re: [PATCH upstream] KASAN: slab-out-of-bounds Read in getname_kernel
To:     tomas <tomasbortoli@gmail.com>
Cc:     Ian Kent <raven@themaw.net>, LKML <linux-kernel@vger.kernel.org>,
        syzkaller <syzkaller@googlegroups.com>, autofs@vger.kernel.org
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On Mon, Jul 2, 2018 at 1:55 PM, tomas <tomasbortoli@gmail.com> wrote:
> Yes, thanks. Please use my full name, Tomas Bortoli.


Please also include:

Reported-by: syzbot+60c837b428dc84e83a93@syzkaller.appspotmail.com

from the original bug report. This this help to keep automatic testing
process running.

Thanks


>
> On 07/02/2018 12:20 PM, Ian Kent wrote:
>> On Mon, 2018-07-02 at 10:31 +0200, tomas wrote:
>>> Hi Ian,
>>>
>>> you are welcome!
>>>
>>> yes your patch is much better. You should just put the "_IOC_NR" macro
>>> around "cmd" in the lines added to "validate_dev_ioctl" to make it work.
>> LOL, yes, that was a dumb mistake.
>>
>> I'll send it to Andrew Morton, after some fairly simple sanity testing,
>> with both our Signed-off-by added.
>>
>>> Tomas
>>>
>>>
>>> On 07/02/2018 03:42 AM, Ian Kent wrote:
>>>> On Mon, 2018-07-02 at 09:10 +0800, Ian Kent wrote:
>>>>> On Mon, 2018-07-02 at 00:04 +0200, tomas wrote:
>>>>>> Hi,
>>>>>>
>>>>>> I've looked into this issue found by Syzbot and I made a patch:
>>>>>>
>>>>>> https://syzkaller.appspot.com/bug?id=d03abd8b42847f7f69b1d1d7f97208ae425
>>>>>> b116
>>>>>> 3
>>>>> Umm ... oops!
>>>>>
>>>>> Thanks for looking into this Tomas.
>>>>>
>>>>>> The autofs subsystem does not check that the "path" parameter is present
>>>>>> within the "param" struct passed by the userspace in case the
>>>>>> AUTOFS_DEV_IOCTL_OPENMOUNT_CMD command is passed. Indeed, it assumes a
>>>>>> path is always provided (though a path is not always present, as per how
>>>>>> the struct is defined:
>>>>>> https://github.com/torvalds/linux/blob/master/include/uapi/linux/auto_de
>>>>>> v-io
>>>>>> ct
>>>>>> l.h#L89).
>>>>>> Skipping the check provokes an oob read in "strlen", called by
>>>>>> "getname_kernel", in turn called by the autofs to assess the length of
>>>>>> the non-existing path.
>>>>>>
>>>>>> To solve it, modify the "validate_dev_ioctl" function to check also that
>>>>>> a path has been provided if the command is
>>>>>> AUTOFS_DEV_IOCTL_OPENMOUNT_CMD.
>>>>>>
>>>>>>
>>>>>> --- b/fs/autofs/dev-ioctl.c    2018-07-01 23:10:16.059728621 +0200around
>>>>>> +++ a/fs/autofs/dev-ioctl.c    2018-07-01 23:10:24.311792133 +0200
>>>>>> @@ -136,6 +136,9 @@ static int validate_dev_ioctl(int cmd, s
>>>>>>              goto out;
>>>>>>          }
>>>>>>      }
>>>>>> +    /* AUTOFS_DEV_IOCTL_OPENMOUNT_CMD without path */
>>>>>> +    else if(_IOC_NR(cmd) == AUTOFS_DEV_IOCTL_OPENMOUNT_CMD)
>>>>>> +        return -EINVAL;
>>>>> My preference is to put the comment inside the else but ...
>>>>>
>>>>> There's another question, should the check be done in
>>>>> autofs_dev_ioctl_openmount() in the same way it's checked in other
>>>>> ioctls that need a path, such as in autofs_dev_ioctl_requester()
>>>>> and autofs_dev_ioctl_ismountpoint()?
>>>>>
>>>>> For consistency I'd say it should.
>>>>>
>>>>>>
>>>>>>      err = 0;You should just put the "_IOC_NR" directive around "cmd" in
>>>>>> the lines added to "validate_dev_ioctl" to make it work.
>>>>>>  out:
>>>>>>
>>>>>>
>>>>>> Tested and solves the issue on Linus' main git tree.
>>>>>>
>>>>>>
>>>> Or perhaps this (not even compile tested) patch would be better?
>>>>
>>>> autofs - fix slab out of bounds read in getname_kernel()
>>>>
>>>> From: Ian Kent <raven@themaw.net>
>>>>
>>>> The autofs subsystem does not check that the "path" parameter is
>>>> present for all cases where it is required when it is passed in
>>>> via the "param" struct.
>>>>
>>>> In particular it isn't checked for the AUTOFS_DEV_IOCTL_OPENMOUNT_CMD
>>>> ioctl command.
>>>>
>>>> To solve it, modify validate_dev_ioctl() function to check that a
>>>> path has been provided for ioctl commands that require it.
>>>> ---
>>>>  fs/autofs/dev-ioctl.c |   15 +++++++--------
>>>>  1 file changed, 7 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/fs/autofs/dev-ioctl.c b/fs/autofs/dev-ioctl.c
>>>> index ea4ca1445ab7..61c63715c3fb 100644
>>>> --- a/fs/autofs/dev-ioctl.c
>>>> +++ b/fs/autofs/dev-ioctl.c
>>>> @@ -135,6 +135,11 @@ static int validate_dev_ioctl(int cmd, struct
>>>> autofs_dev_ioctl *param)
>>>>                             cmd);
>>>>                     goto out;
>>>>             }
>>>> +   } else if (cmd == AUTOFS_DEV_IOCTL_OPENMOUNT_CMD ||
>>>> +              cmd == AUTOFS_DEV_IOCTL_REQUESTER_CMD ||
>>>> +              cmd == AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD) {
>>>> +           err = -EINVAL;
>>>> +           goto out;
>>>>     }
>>>>
>>>>     err = 0;
>>>> @@ -433,10 +438,7 @@ static int autofs_dev_ioctl_requester(struct file *fp,
>>>>     dev_t devid;
>>>>     int err = -ENOENT;
>>>>
>>>> -   if (param->size <= AUTOFS_DEV_IOCTL_SIZE) {
>>>> -           err = -EINVAL;
>>>> -           goto out;
>>>> -   }
>>>> +   /* param->path has already been checked */
>>>>
>>>>     devid = sbi->sb->s_dev;
>>>>
>>>> @@ -521,10 +523,7 @@ static int autofs_dev_ioctl_ismountpoint(struct file
>>>> *fp,
>>>>     unsigned int devid, magic;
>>>>     int err = -ENOENT;
>>>>
>>>> -   if (param->size <= AUTOFS_DEV_IOCTL_SIZE) {
>>>> -           err = -EINVAL;
>>>> -           goto out;
>>>> -   }
>>>> +   /* param->path has already been checked */
>>>>
>>>>     name = param->path;
>>>>     type = param->ismountpoint.in.type;
>>>
>
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