linux-kernel - [34-longterm 176/209] tracing: Fix panic when lseek() called on "trace" opened for writing

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Date:	Thu, 14 Apr 2011 13:55:34 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	stable@...nel.org, linux-kernel@...r.kernel.org
Cc:	stable-review@...nel.org, Slava Pestov <slavapestov@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [34-longterm 176/209] tracing: Fix panic when lseek() called on "trace" opened for writing

From: Slava Pestov <slavapestov@...gle.com>

  =====================================================================
  | This is a commit scheduled for the next v2.6.34 longterm release. |
  | If you see a problem with using this for longterm, please comment.|
  =====================================================================

commit 364829b1263b44aa60383824e4c1289d83d78ca7 upstream.

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.

Signed-off-by: Slava Pestov <slavapestov@...gle.com>
LKML-Reference: <1290640396-24179-1-git-send-email-slavapestov@...gle.com>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 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 44f916a..eb76a22 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2341,11 +2341,19 @@ 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,
 };
 
-- 
1.7.4.4

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