Re: [PATCH] fuse: Fix IOC_[GS]ETFLAGS argument size brokenness

[Richard Hansen <rhansen@rhansen.org>]

On 2013-12-19 18:27, Darrick J. Wong wrote:
> The IOC_[GS]ETFLAGS 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, and document this int/long quirk in
> include/uapi/linux/fs.h.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/fuse/file.c          |   11 +++++++++++
>  include/uapi/linux/fs.h |    1 +
>  2 files changed, 12 insertions(+)
> 
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 7e70506..5fa8181 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -2385,6 +2385,17 @@ 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 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.
> +		 */
> +		if (cmd == FS_IOC_GETFLAGS || cmd == FS_IOC_SETFLAGS) {
> +			iov->iov_len = sizeof(int);
> +		}
> +
>  		if (_IOC_DIR(cmd) & _IOC_WRITE) {
>  			in_iov = iov;
>  			in_iovs = 1;
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 6c28b61..bc8aa8e 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -154,6 +154,7 @@ struct inodes_stat_t {
>  #define FITHAW		_IOWR('X', 120, int)	/* Thaw */
>  #define FITRIM		_IOWR('X', 121, struct fstrim_range)	/* Trim */
>  
> +/* IOC_[GS]ETFLAGS take an int argument despite being defined to take long. */
>  #define	FS_IOC_GETFLAGS			_IOR('f', 1, long)
>  #define	FS_IOC_SETFLAGS			_IOW('f', 2, long)
>  #define	FS_IOC_GETVERSION		_IOR('v', 1, long)

This change to include/uapi/linux/fs.h is similar to but not as thorough as:

http://mid.gmane.org/1385548839-16617-1-git-send-email-aurelien@aurel32.net
https://lkml.org/lkml/2013/11/27/93

(The above linked patch is the patch Aurelien referenced in the
"Argument type for FS_IOC_GETFLAGS/FS_IOC_SETFLAGS ioctls" thread on
linux-fsdevel; see
<http://mid.gmane.org/20131127231430.GG29912@hall.aurel32.net>.)

-Richard