Re: [PATCH] autofs4: Do not potentially dereference NULL pointer returned by fget() in autofs_dev_ioctl_setpipefd()

[Ian Kent <raven@themaw.net>]

On Sat, 2010-12-18 at 22:43 +0100, Jesper Juhl wrote:
> Hi,
> 
> In fs/autofs4/dev-ioctl.c::autofs_dev_ioctl_setpipefd() we call fget(), 
> which may return NULL, but we do not explicitly test for that NULL return 
> so we may end up dereferencing a NULL pointer - bad.
> 
> When I originally submitted this patch I had chosen EBUSY as the return 
> value to use if this happens. Ian Kent was kind enough to explain why that 
> would most likely be wrong and why EBADF should most likely be used 
> instead. This version of the patch uses EBADF.
> 
> 
> Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Acked-by: Ian Kent <raven@themaw.net>

> ---
>  dev-ioctl.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
> index eff9a41..a650d7e 100644
> --- a/fs/autofs4/dev-ioctl.c
> +++ b/fs/autofs4/dev-ioctl.c
> @@ -372,6 +372,10 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp,
>  		return -EBUSY;
>  	} else {
>  		struct file *pipe = fget(pipefd);
> +		if (!pipe) {
> +			err = -EBADF;
> +			goto out;
> +		}
>  		if (!pipe->f_op || !pipe->f_op->write) {
>  			err = -EPIPE;
>  			fput(pipe);
> 
> 
>