• Al Viro's avatar
    tracing: Fix buggered tee(2) on tracing_pipe · 92fdd98c
    Al Viro authored
    
    
    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: default avatarAl Viro <viro@zeniv.linux.org.uk>
    [ SDR - Removed no longer used tracing_pipe_buf_release ]
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    92fdd98c
trace.c 154 KB