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

From: Paul Gortmaker
Date: Thu Apr 14 2011 - 13:58:54 EST

From: Slava Pestov <slavapestov@xxxxxxxxxx>

| 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@xxxxxxxxxx>
LKML-Reference: <1290640396-24179-1-git-send-email-slavapestov@xxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
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,


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