On Mon, Jul 13, 2026 at 08:28:23AM +0100, Fuad Tabba wrote:
> 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.
>
> Fixes: 96e43537af546 ("tracing: Introduce trace remotes")
> Signed-off-by: Fuad Tabba <[email protected]>
Reviewed-by: Vincent Donnefort <[email protected]>
Tested-by: Vincent Donnefort <[email protected]>
> ---
> I found this while reviewing Vincent's series [1].
>
> Applies on top of Vincent's "[PATCH v2 0/3] tracing/remotes: Fix leak in
> trace_remote_alloc_buffer() error path" [2], which fixes the other
> issues in this function.
>
> [1]
> https://lore.kernel.org/all/[email protected]/
> [2]
> https://lore.kernel.org/all/[email protected]/
>
> 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 0f6ef5c36d84e..ef42d9c38b374 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);
> }
>
> base-commit: 8cdeaa50eae8dad34885515f62559ee83e7e8dda
> prerequisite-patch-id: 8bdd7b28f09e97cff4f5995196b83b377c961d8b
> prerequisite-patch-id: 6781b7ce5156d229fd21a757ef0cd66dd76130cc
> prerequisite-patch-id: 56bcbbdceddf4533770d48d1835d5b7e11f47d56
> --
> 2.39.5
>
