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| author | Steven Rostedt (Red Hat) <rostedt@goodmis.org> | 2016-09-23 22:57:13 -0400 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2016-11-20 01:17:35 +0000 |
| commit | e044d0e8ca650435f1fc6133cff1b86441fe63d9 (patch) | |
| tree | a125eb93d0a9bc4b10dd288bb0f901a3d113b1c8 | |
| parent | e071c8d1e0f95f8fde2effb0419ed2e9e5b4ea3d (diff) | |
| download | lwn-e044d0e8ca650435f1fc6133cff1b86441fe63d9.tar.gz lwn-e044d0e8ca650435f1fc6133cff1b86441fe63d9.zip | |
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 <viro@ZenIV.linux.org.uk>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
| -rw-r--r-- | kernel/trace/trace.c | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 6d3c38966eda..8df0ed9af291 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) |