linux-kernel - Re: [PATCH] ftrace: Fix panic when lseek() called on "trace" opened for writing

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Date:	Wed, 24 Nov 2010 15:34:17 -0800
From:	David Sharp <dhsharp@...gle.com>
To:	Slava Pestov <slavapestov@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, mrubin@...gle.com
Subject: Re: [PATCH] ftrace: Fix panic when lseek() called on "trace" opened
 for writing

On Wed, Nov 24, 2010 at 3:13 PM, Slava Pestov <slavapestov@...gle.com> wrote:
> The file_ops struct for the "trace" special file defined llseek as seq_lseek().
> However, if the file was opened for writing only, seq_open() was not called,
> and the seek would dereference a null pointer, file->private_data.
>
> This patch introduces a new wrapper for seq_lseek() which checks if the file
> descriptor is opened for reading first. If not, it does nothing.
>
> This patch is for Linux 2.6.36.1.
>
> Signed-Off-By: Slava Pestov <slavapestov@...gle.com>

Cc: Steven Rostedt <rostedt@...dmis.org>

> ---
>
> Change-Id: Iaabc50d84fb541c04e3efabd4788cebadbadbb4c
> ---
>  kernel/trace/trace.c |   10 +++++++++-
>  1 files changed, 9 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 9ec59f5..7702f5a 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2320,11 +2320,19 @@ tracing_write_stub(struct file *filp, const char __user *ubuf,
>        return count;
>  }
>
> +static loff_t tracing_seek(struct file *file, loff_t offset, int origin)
> +{
> +       if (file->f_mode & FMODE_READ)
> +               return seq_lseek(file, offset, origin);
> +       else
> +               return 0;
> +}
> +
>  static const struct file_operations tracing_fops = {
>        .open           = tracing_open,
>        .read           = seq_read,
>        .write          = tracing_write_stub,
> -       .llseek         = seq_lseek,
> +       .llseek         = tracing_seek,
>        .release        = tracing_release,
>  };
>
> --
> 1.7.3.1
>
>
--
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