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 @@
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 @@
.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,
};
