7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Donggeun Yoo commit 25132363c723afc39aace8b098f547ab4a0ea759 upstream. On a persistent ring buffer, rb_meta_subbuf_idx() can return an index one sub-buffer too high. rb_setup_ids_meta_page() then fills subbuf_ids[] shifted by one and leaves subbuf_ids[0] NULL, which __rb_map_vma() dereferences when userspace maps trace_pipe_raw. rb_update_meta_reader() writes two such indices into meta->buffers[], which rb_cpu_meta_valid() would reject on the next boot, discarding the previous boot's trace. A CPU's sub-buffer array starts after its meta header and the nr_subbufs integers that follow, aligned up to a sub-buffer. rb_meta_subbuf_idx() inverts that calculation but skips only the integers, not the header, so its base is one sub-buffer low whenever the omitted header size crosses the alignment boundary. Invert the calculation with rb_subbufs_from_meta() rather than repeating it. rb_range_buffer() maps an index back to an address through the same helper, so the two directions can no longer disagree. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260918071507.1019251-1-donggeunyoo.kernel@gmail.com Fixes: b14d032973d4 ("ring-buffer: Add ring_buffer_meta data") Signed-off-by: Donggeun Yoo Reviewed-by: Vincent Donnefort Acked-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt Signed-off-by: Greg Kroah-Hartman --- kernel/trace/ring_buffer.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -3616,10 +3616,8 @@ static void rb_inc_iter(struct ring_buff /* Return the index into the sub-buffers for a given sub-buffer */ static int rb_meta_subbuf_idx(struct ring_buffer_cpu_meta *meta, void *subbuf) { - void *subbuf_array; + void *subbuf_array = rb_subbufs_from_meta(meta); - subbuf_array = (void *)meta + sizeof(int) * meta->nr_subbufs; - subbuf_array = (void *)ALIGN((unsigned long)subbuf_array, meta->subbuf_size); return (subbuf - subbuf_array) / meta->subbuf_size; }