From 94b83ff0c0a69e42f403b59918529fbca2a89daf Mon Sep 17 00:00:00 2001 From: Fuad Tabba Date: Mon, 13 Jul 2026 08:28:23 +0100 Subject: [PATCH] tracing/remotes: Fix page_va[] access before counter update in trace_remote_alloc_buffer() page_va[] is annotated __counted_by(nr_page_va), so nr_page_va must cover an index before that element is accessed. The allocation loop writes page_va[id] while nr_page_va is still id and increments it only afterwards, so every write is one element past the declared count. The store is out of bounds with respect to the annotation: a build with CONFIG_UBSAN_BOUNDS on a toolchain that honours __counted_by (clang >= 20.1, gcc >= 15.1) flags it as an array-index overflow. Increment nr_page_va before writing the element it now covers. A failed allocation then leaves the slot counted but NULL; the error path frees it with free_page(0), which is a no-op. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260713072823.2668323-1-fuad.tabba@linux.dev Fixes: 96e43537af546 ("tracing: Introduce trace remotes") Signed-off-by: Fuad Tabba Reviewed-by: Vincent Donnefort Tested-by: Vincent Donnefort Signed-off-by: Steven Rostedt --- kernel/trace/trace_remote.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 0f6ef5c36d84..ef42d9c38b37 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -1004,11 +1004,10 @@ int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t desc_size, desc->nr_cpus++; for (id = 0; id < nr_pages; id++) { + rb_desc->nr_page_va++; rb_desc->page_va[id] = (unsigned long)__get_free_page(GFP_KERNEL); if (!rb_desc->page_va[id]) goto err; - - rb_desc->nr_page_va++; } rb_desc = __next_ring_buffer_desc(rb_desc); }