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: v3.10.105~40 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0d75118c756e5c47dbb5394e3ad1d896d6f80285;p=thirdparty%2Fkernel%2Fstable.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: Willy Tarreau --- diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 4ff36f73f1a32..d6e72522fc4e0 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4121,13 +4121,6 @@ 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)) @@ -4140,6 +4133,14 @@ 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)