linux-kernel - Re: [PATCH upstream] KASAN: slab-out-of-bounds Read in getname

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Message-ID: <1bbf3634-6c2a-f40e-a9d3-9d6ffc9a0562@gmail.com>
Date:   Mon, 2 Jul 2018 10:31:34 +0200
From:   tomas <tomasbortoli@...il.com>
To:     Ian Kent <raven@...maw.net>
Cc:     linux-kernel@...r.kernel.org, syzkaller@...glegroups.com,
        autofs@...r.kernel.org
Subject: Re: [PATCH upstream] KASAN: slab-out-of-bounds Read in getname_kernel

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.

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=d03abd8b42847f7f69b1d1d7f97208ae425b116
>>> 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_dev-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@...maw.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;