Commit abd91e8b authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Sasha Levin

tracing: Move mutex to protect against resetting of seq data

[ Upstream commit 1245800c ]

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>
Signed-off-by: default avatarSasha Levin <alexander.levin@verizon.com>
parent 7d0e5777
...@@ -4694,19 +4694,20 @@ tracing_read_pipe(struct file *filp, char __user *ubuf, ...@@ -4694,19 +4694,20 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
struct trace_iterator *iter = filp->private_data; struct trace_iterator *iter = filp->private_data;
ssize_t sret; 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 * Avoid more than one consumer on a single file descriptor
* This is just a matter of traces coherency, the ring buffer itself * This is just a matter of traces coherency, the ring buffer itself
* is protected. * is protected.
*/ */
mutex_lock(&iter->mutex); 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) { if (iter->trace->read) {
sret = iter->trace->read(iter, filp, ubuf, cnt, ppos); sret = iter->trace->read(iter, filp, ubuf, cnt, ppos);
if (sret) if (sret)
......
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