Re: [PATCH] ftrace: Fix panic when lseek() called on "trace" openedfor writing

[David Sharp]

On Wed, Nov 24, 2010 at 3:13 PM, Slava Pestov <slavapestov@xxxxxxxxxx> 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@xxxxxxxxxx>

Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>

> ---
>
> Change-Id: Iaabc50d84fb541c04e3efabd4788cebadbadbb4c
> ---
> Âkernel/trace/trace.c | Â 10 +++++++++-
> Â1 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,
> Â Â Â Âreturn count;
> Â}
>
> +static loff_t tracing_seek(struct file *file, loff_t offset, int origin)
> +{
> + Â Â Â if (file->f_mode & FMODE_READ)
> + Â Â Â Â Â Â Â return seq_lseek(file, offset, origin);
> + Â Â Â else
> + Â Â Â Â Â Â Â return 0;
> +}
> +
> Âstatic const struct file_operations tracing_fops = {
>    Â.open      = tracing_open,
>    Â.read      = seq_read,
>    Â.write     Â= tracing_write_stub,
> -    .llseek     = seq_lseek,
> +    .llseek     = tracing_seek,
>    Â.release    Â= tracing_release,
> Â};
>
> --
> 1.7.3.1
>
>
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