Commit 364829b1 authored Nov 24, 2010 by Slava Pestov Committed by Steven Rostedt Nov 30, 2010

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>

parent 60e67737

kernel/trace/trace.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -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,
		};

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