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


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