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: v3.16.39~28 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=e044d0e8ca650435f1fc6133cff1b86441fe63d9;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 [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings --- diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 6d3c38966eda2..8df0ed9af2919 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4435,13 +4435,6 @@ 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)) @@ -4454,6 +4447,14 @@ 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)