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Commit 1245800c authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Steven Rostedt
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tracing: Move mutex to protect against resetting of seq data 



The iter->seq can be reset outside the protection of the mutex. So can
reading of user data. Move the mutex up to the beginning of the function.

Fixes: d7350c3f ("tracing/core: make the read callbacks reentrants")
Cc: stable@vger.kernel.org # 2.6.30+
Reported-by: default avatarAl Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent c87edb36

kernel/trace/trace.c

+8 −7
Original line number Diff line number Diff line
@@ -4890,19 +4890,20 @@ tracing_read_pipe(struct file *filp, char __user *ubuf, 
	struct trace_iterator *iter = filp->private_data;

	ssize_t sret;



	/* return any leftover data */

	sret = trace_seq_to_user(&iter->seq, ubuf, cnt);

	if (sret != -EBUSY)

		return sret;



	trace_seq_init(&iter->seq);



	/*

	 * Avoid more than one consumer on a single file descriptor

	 * This is just a matter of traces coherency, the ring buffer itself

	 * is protected.

	 */

	mutex_lock(&iter->mutex);



	/* return any leftover data */

	sret = trace_seq_to_user(&iter->seq, ubuf, cnt);

	if (sret != -EBUSY)

		goto out;



	trace_seq_init(&iter->seq);



	if (iter->trace->read) {

		sret = iter->trace->read(iter, filp, ubuf, cnt, ppos);

		if (sret)