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

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

[Slava Pestov]

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@google.com>
---

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

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

[David Sharp]

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

Cc: Steven Rostedt <rostedt@goodmis.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
>
>

[tip:perf/urgent] tracing: Fix panic when lseek() called on "trace" opened for writing

[tip-bot for Slava Pestov]

Commit-ID:  364829b1263b44aa60383824e4c1289d83d78ca7
Gitweb:     http://git.kernel.org/tip/364829b1263b44aa60383824e4c1289d83d78ca7
Author:     Slava Pestov <slavapestov@google.com>
AuthorDate: Wed, 24 Nov 2010 15:13:16 -0800
Committer:  Steven Rostedt <rostedt@goodmis.org>
CommitDate: Tue, 30 Nov 2010 12:18:17 -0500

tracing: Fix panic when lseek() called on "trace" opened for writing

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.

Cc: <stable@kernel.org>
Signed-off-by: Slava Pestov <slavapestov@google.com>
LKML-Reference: <1290640396-24179-1-git-send-email-slavapestov@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 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 ee6a733..21db0de 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2339,11 +2339,19 @@ 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,
 };