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
