| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.7 32/69] tracing: Move mutex to protect against resetting of seq data | Date | Wed, 28 Sep 2016 11:05:14 +0200 |
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4.7-stable review patch. If anyone has any objections, please let me know.
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From: Steven Rostedt (Red Hat) <rostedt@goodmis.org>
commit 1245800c0f96eb6ebb368593e251d66c01e61022 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: d7350c3f45694 ("tracing/core: make the read callbacks reentrants") Reported-by: Al Viro <viro@ZenIV.linux.org.uk> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- kernel/trace/trace.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-)
--- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4890,19 +4890,20 @@ tracing_read_pipe(struct file *filp, cha 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)
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