On Wed, Aug 12, 2026 at 03:50:37PM +0000, [email protected] wrote: > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) > to consider: > > Pre-existing issues: > - [Critical] Concurrent execution of sub-buffer order resizing > (`ring_buffer_subbuf_order_set`) and read operations > (`ring_buffer_alloc_read_page`, `ring_buffer_read_page`) can lead to > out-of-bounds writes, use-after-free, and page allocator corruption due to > mismatched synchronization. > -- > > --- Patch [1]: [PATCH v4 1/9] ring-buffer: Free cpu_buffer->free_page with > subbuf_order --- > commit 4100674474d6bd293fb872fecb17fc781ca58502 > Author: Vincent Donnefort <[email protected]> > > ring-buffer: Free cpu_buffer->free_page with subbuf_order > > When sub-buffers use an order greater than 0, cpu_buffer->free_page is > allocated with subbuf_order. Use the correct order for > cpu_buffer->free_page. > > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > > index 2667992f0aa29..a3d28b2e2c94a 100644 > > --- a/kernel/trace/ring_buffer.c > > +++ b/kernel/trace/ring_buffer.c > > @@ -2631,7 +2631,7 @@ static void rb_free_cpu_buffer(struct > > ring_buffer_per_cpu *cpu_buffer) > > free_buffer_page(bpage); > > } > > > > - free_page((unsigned long)cpu_buffer->free_page); > > + free_pages((unsigned long)cpu_buffer->free_page, > > cpu_buffer->buffer->subbuf_order); > > [Severity: Critical] > This isn't a bug introduced by this patch, but is it possible for a race > condition between resizing and reading to lead to memory corruption? > > If thread A changes the sub-buffer size via > /sys/kernel/tracing/buffer_subbuf_size_kb, ring_buffer_subbuf_order_set() > updates buffer->subbuf_order locklessly globally before tearing down the CPU > buffers and clearing their free_page. > > If thread B concurrently reads /sys/kernel/tracing/per_cpu/cpu0/trace_pipe_raw > via tracing_buffers_read(), it observes the new order and calls > ring_buffer_alloc_read_page(). > > Because ring_buffer_subbuf_order_set() hasn't yet cleared > cpu_buffer->free_page for this CPU (they use distinct locks), thread B pops > the old page from free_page but tags it with the new order: > > kernel/trace/ring_buffer.c:ring_buffer_alloc_read_page() { > ... > bpage->order = buffer->subbuf_order; > ... > if (cpu_buffer->free_page) { > bpage->data = cpu_buffer->free_page; > cpu_buffer->free_page = NULL; > } > ... > } > > Thread B then calls ring_buffer_read_page(). The lockless check passes > because both match the new order: > > kernel/trace/ring_buffer.c:ring_buffer_read_page() { > ... > if (data_page->order != buffer->subbuf_order) > return -1; > ... > reader->page = data_page->data; > } > > Could this allow the undersized old page to be swapped into the ring buffer > as the reader_page, leading to an out-of-bounds write when a writer attempts > to write large events? > > It seems it could also cause page allocator corruption when a smaller page > is later passed to free_pages() with a larger order. > > > kfree(cpu_buffer); > > } > > -- > Sashiko AI review ยท > https://sashiko.dev/#/patchset/[email protected]?part=1
All that is hopefully fixed in one of the later patch of the series -- Vincent
