From: Al Viro <viro@ZenIV.linux.org.uk>
Date: Fri, 17 Jan 2014 12:53:39 +0000 (-0500)
Subject: tracing: Fix buggered tee(2) on tracing_pipe
X-Git-Tag: accepted/tizen/common/20141203.182822~707^2~3
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=92fdd98cf8bdec4d6b0c510e2f073ac4fd059be8;p=platform%2Fkernel%2Flinux-arm64.git

tracing: Fix buggered tee(2) on tracing_pipe

In kernel/trace/trace.c we have this:
static void tracing_pipe_buf_release(struct pipe_inode_info *pipe,
                                     struct pipe_buffer *buf)
{
        __free_page(buf->page);
}
static const struct pipe_buf_operations tracing_pipe_buf_ops = {
        .can_merge              = 0,
        .map                    = generic_pipe_buf_map,
        .unmap                  = generic_pipe_buf_unmap,
        .confirm                = generic_pipe_buf_confirm,
        .release                = tracing_pipe_buf_release,
        .steal                  = generic_pipe_buf_steal,
        .get                    = generic_pipe_buf_get,
};
with
void generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
{
        page_cache_get(buf->page);
}

and I don't see anything that would've prevented tee(2) called on the pipe
that got stuff spliced into it from that sucker.  ->ops->get() will be
called, then buf gets copied into target pipe's ->bufs[] and eventually
readers get to both copies of the buffer.  With
	get_page(page)
	look at that page
	__free_page(page)
	look at that page
	__free_page(page)
which is not a good thing, to put it mildly.  AFAICS, that ought to use
the normal generic_pipe_buf_release() (aka page_cache_release(buf->page)),
shouldn't it?

[
 SDR - As trace_pipe just allocates the page with alloc_page(GFP_KERNEL),
  and doesn't do anything special with it (no LRU logic). The __free_page()
  should be fine, as it wont actually free a page with reference count.
  Maybe there's a chance to leak memory? Anyway, This change is at a minimum
  good for being symmetric with generic_pipe_buf_get, it is fine to add.
]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[ SDR - Removed no longer used tracing_pipe_buf_release ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index cee9c1a..20c755e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4243,12 +4243,6 @@ out:
 	return sret;
 }
 
-static void tracing_pipe_buf_release(struct pipe_inode_info *pipe,
-				     struct pipe_buffer *buf)
-{
-	__free_page(buf->page);
-}
-
 static void tracing_spd_release_pipe(struct splice_pipe_desc *spd,
 				     unsigned int idx)
 {
@@ -4260,7 +4254,7 @@ static const struct pipe_buf_operations tracing_pipe_buf_ops = {
 	.map			= generic_pipe_buf_map,
 	.unmap			= generic_pipe_buf_unmap,
 	.confirm		= generic_pipe_buf_confirm,
-	.release		= tracing_pipe_buf_release,
+	.release		= generic_pipe_buf_release,
 	.steal			= generic_pipe_buf_steal,
 	.get			= generic_pipe_buf_get,
 };