linux-kernel - Re: [PATCH] firmware/efi: Fix a use after bug in efi_mem_reserve

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Message-ID: <CAMj1kXESeiozq=DAsYsKOP6DVEOQknPqUdam_LpRiPzhLhCCBg@mail.gmail.com>
Date:   Thu, 18 Mar 2021 19:17:40 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Lv Yunlong <lyl2019@...l.ustc.edu.cn>
Cc:     jonathan.richardson@...adcom.com,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] firmware/efi: Fix a use after bug in efi_mem_reserve_persistent

On Wed, 10 Mar 2021 at 09:37, Lv Yunlong <lyl2019@...l.ustc.edu.cn> wrote:
>
> In the for loop in efi_mem_reserve_persistent(), prsv = rsv->next
> use the unmapped rsv. Use the unmapped pages will cause segment
> fault.
>
> Fixes: 18df7577adae6 ("efi/memreserve: deal with memreserve entries in unmapped memory")
> Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>

Queued as a fix, thanks.

> ---
>  drivers/firmware/efi/efi.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index df3f9bcab581..4b7ee3fa9224 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -927,7 +927,7 @@ 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; prsv = rsv->next) {
> +       for (prsv = efi_memreserve_root->next; prsv; ) {
>                 rsv = memremap(prsv, sizeof(*rsv), MEMREMAP_WB);
>                 index = atomic_fetch_add_unless(&rsv->count, 1, rsv->size);
>                 if (index < rsv->size) {
> @@ -937,6 +937,7 @@ int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
>                         memunmap(rsv);
>                         return efi_mem_reserve_iomem(addr, size);
>                 }
> +               prsv = rsv->next;
>                 memunmap(rsv);
>         }
>
> --
> 2.25.1
>
>