linux-kernel - Re: [PATCH v2] fuse: Fix IOC_[GS]ET{FLAGS,VERSION} argument size brokenness.

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Message-Id: <99199002-0C82-42B6-B237-163561AD821B@dilger.ca>
Date:	Fri, 20 Dec 2013 19:09:23 -0700
From:	Andreas Dilger <adilger@...ger.ca>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"fuse-devel@...ts.sourceforge.net" <fuse-devel@...ts.sourceforge.net>,
	Richard Hansen <rhansen@...nsen.org>
Subject: Re: [PATCH v2] fuse: Fix IOC_[GS]ET{FLAGS,VERSION} argument size brokenness.

To be honest, FS_IOC_SETVERSION isn't used by many/any users, so it might be better to avoid doing anything with that for now.

In the past we even talked about adding a deprecation warning for that ioctl since it adds complexity for little value. 

Cheers, Andreas

> On Dec 20, 2013, at 16:35, "Darrick J. Wong" <darrick.wong@...cle.com> wrote:
> 
> The IOC_[GS]ETFLAGS and IOC_[GS]ETVERSION ioctls, despite being
> defined to take a "long" parameter, actually take "int" parameters.
> FUSE unfortunately assumed that the ioctl definitions never lie, and
> transfers a long's worth of data in and out of userspace, which causes
> stack smashing in chattr, and other bugs elsewhere.
> 
> So, special-case this in FUSE so that we don't crash userland.
> 
> v2: Do the same for the IOC_[GS]ETVERSION ioctls, as Richard Hansen
>    points out.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> ---
> fs/fuse/file.c |   16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
> 
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 7e70506..f8766ab 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -2385,6 +2385,22 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
>        iov->iov_base = (void __user *)arg;
>        iov->iov_len = _IOC_SIZE(cmd);
> 
> +        /*
> +         * The IOC_[GS]ETFLAGS and IOC_[GS]ETVERSION ioctls take int
> +         * parameters even though the ioctl definition specifies long.
> +         * Userland has been expecting int for ages (and chattr
> +         * segfaults on FUSE filesystems), so special case that here.
> +         * The IOC32 variants were declared with int, so they don't
> +         * need this correction.
> +         */
> +        switch (cmd) {
> +        case FS_IOC_GETFLAGS:
> +        case FS_IOC_SETFLAGS:
> +        case FS_IOC_GETVERSION:
> +        case FS_IOC_SETVERSION:
> +            iov->iov_len = sizeof(int);
> +        }
> +
>        if (_IOC_DIR(cmd) & _IOC_WRITE) {
>            in_iov = iov;
>            in_iovs = 1;
> --
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