Re: [PATCH] efi: fix potential NULL deref in efi_mem_reserve_persistent

[Ard Biesheuvel]

On Fri, 3 Feb 2023 at 14:23, Anton Gusev <aagusev@xxxxxxxxx> wrote:
>
> When iterating on a linked list, a result of memremap is dereferenced
> without checking it for NULL.
>
> This patch adds a check that falls back on allocating a new page in
> case memremap doesn't succeed.
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Fixes: 18df7577adae ("efi/memreserve: deal with memreserve entries in unmapped memory")
> Signed-off-by: Anton Gusev <aagusev@xxxxxxxxx>
> ---
>  drivers/firmware/efi/efi.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index a2b0cbc8741c..48d30c806d94 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -1007,6 +1007,8 @@ int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
>         /* first try to find a slot in an existing linked list entry */
>         for (prsv = efi_memreserve_root->next; prsv; ) {
>                 rsv = memremap(prsv, sizeof(*rsv), MEMREMAP_WB);
> +               if (!rsv)
> +                       break;

Thanks for the patch.

Why do you think 'break' is the correct action here?


>                 index = atomic_fetch_add_unless(&rsv->count, 1, rsv->size);
>                 if (index < rsv->size) {
>                         rsv->entry[index].base = addr;
> --
> 2.39.1
>