Commit cc2b40c4 authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Jiri Slaby

tracing: Move mutex to protect against resetting of seq data

commit 1245800c upstream.

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")
Reported-by: default avatarAl Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarJiri Slaby <jslaby@suse.cz>
parent c46e22a8
......@@ -4132,13 +4132,6 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
struct trace_array *tr = iter->tr;
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);
/* copy the tracer to avoid using a global lock all around */
mutex_lock(&trace_types_lock);
if (unlikely(iter->trace->name != tr->current_trace->name))
......@@ -4151,6 +4144,14 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
* 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)
......
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