From: Steven Rostedt (Red Hat) Date: Sat, 24 Sep 2016 02:57:13 +0000 (-0400) Subject: tracing: Move mutex to protect against resetting of seq data X-Git-Tag: firefly_0821_release~176^2~4^2~27^2~20 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=8b275b4522af2b19072df7aee87fd659e09d29bc;p=firefly-linux-kernel-4.4.55.git tracing: Move mutex to protect against resetting of seq data 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 Signed-off-by: Steven Rostedt Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 3a44903169ec..059233abcfcf 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4727,19 +4727,20 @@ 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)