Re: [PATCH] ACPI: pfr_update: fix stack buffer overflow in query_capability()

[Rafael J. Wysocki (Intel)]

On Thu, Aug 6, 2026 at 5:17 PM Anirudh Prasad <icarus@xxxxxxxx> wrote:
>
> > If the firmware wants the kernel to copy more data than the latter has
> > room for, the operation should fail instead of pretending to succeed.
>
> Agreed. v2 validates all four buffer lengths upfront and returns
> -EINVAL if any exceeds its destination field size.

Can you please resend this afresh with proper versioning?

> ---
>
> query_capability() copies four ACPI buffer objects returned by the
> firmware _DSM into fixed-size u8[16] fields in struct
> pfru_update_cap_info using memcpy with the firmware-supplied length:
>
>   memcpy(&cap_hdr->code_type,
>          elements[CAP_CODE_TYPE_IDX].buffer.pointer,
>          elements[CAP_CODE_TYPE_IDX].buffer.length);
>
> The same pattern repeats for drv_type, platform_id, and oem_id.
> If the firmware returns buffer.length > 16 for any of these fields,
> memcpy writes past the destination array.
>
> struct pfru_update_cap_info is stack-allocated in pfru_ioctl().
> Confirmed with KASAN on 7.2-rc6: three stack-out-of-bounds reports
> are generated when a DSM returns 64-byte buffers, with writes reaching
> 44 bytes past the end of cap_hdr's [64, 156) frame window into
> adjacent stack redzones.
>
> Fix by validating each buffer length against its destination field
> size before copying, and returning -EINVAL if the firmware supplies
> an oversized buffer.
>
> Fixes: 0db89fa243e5 ("ACPI: Introduce Platform Firmware Runtime Update device driver")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Anirudh Prasad <icarus@xxxxxxxx>
> ---
>  drivers/acpi/pfr_update.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/drivers/acpi/pfr_update.c b/drivers/acpi/pfr_update.c
> index 6283105bb0e8..e14e053cea44 100644
> --- a/drivers/acpi/pfr_update.c
> +++ b/drivers/acpi/pfr_update.c
> @@ -158,6 +158,14 @@ static int query_capability(struct pfru_update_cap_info *cap_hdr,
>                 goto free_acpi_buffer;
>         }
>
> +       if (out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.length > sizeof(cap_hdr->code_type) ||
> +           out_obj->package.elements[CAP_DRV_TYPE_IDX].buffer.length > sizeof(cap_hdr->drv_type) ||
> +           out_obj->package.elements[CAP_PLAT_ID_IDX].buffer.length > sizeof(cap_hdr->platform_id) ||
> +           out_obj->package.elements[CAP_OEM_ID_IDX].buffer.length > sizeof(cap_hdr->oem_id)) {
> +               ret = -EINVAL;
> +               goto free_acpi_buffer;
> +       }
> +
>         cap_hdr->update_cap = out_obj->package.elements[CAP_UPDATE_IDX].integer.value;
>         memcpy(&cap_hdr->code_type,
>                out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.pointer,
> --
> 2.55.0
>
>
>
>
>
> From: Anirudh Prasad <icarus@xxxxxxxx>
> To: "linux-acpi"<linux-acpi@xxxxxxxxxxxxxxx>
> Cc: "rafaeljwysocki"<rafael.j.wysocki@xxxxxxxxx>, "linux-kernel"<linux-kernel@xxxxxxxxxxxxxxx>, "stable"<stable@xxxxxxxxxxxxxxx>
> Date: Thu, 06 Aug 2026 19:10:59 +0530
> Subject: [PATCH] ACPI: pfr_update: fix stack buffer overflow in query_capability()
>
>  > query_capability() copies four ACPI buffer objects returned by the
>  > firmware _DSM into fixed-size u8[16] fields in struct
>  > pfru_update_cap_info using memcpy with the firmware-supplied length:
>  >
>  >  memcpy(&cap_hdr->code_type,
>  >  elements[CAP_CODE_TYPE_IDX].buffer.pointer,
>  >  elements[CAP_CODE_TYPE_IDX].buffer.length);
>  >
>  > The same pattern repeats for drv_type, platform_id, and oem_id.
>  > If the firmware returns buffer.length > 16 for any of these fields,
>  > memcpy writes past the destination array.
>  >
>  > struct pfru_update_cap_info is stack-allocated in pfru_ioctl().
>  > Confirmed with KASAN on 7.2-rc6: three stack-out-of-bounds reports
>  > are generated when a DSM returns 64-byte buffers, with writes reaching
>  > 44 bytes past the end of cap_hdr's [64, 156) frame window into
>  > adjacent stack redzones.
>  >
>  > Fix by clamping each memcpy length to the size of its destination
>  > field with min_t(u32, buffer.length, sizeof(cap_hdr->field)).
>  >
>  > Fixes: 0db89fa243e5 ("ACPI: Introduce Platform Firmware Runtime Update device driver")
>  > Cc: stable@xxxxxxxxxxxxxxx
>  > Signed-off-by: Anirudh Prasad <icarus@xxxxxxxx>
>  > ---
>  >  drivers/acpi/pfr_update.c | 12 ++++++++----
>  >  1 file changed, 8 insertions(+), 4 deletions(-)
>  >
>  > diff --git a/drivers/acpi/pfr_update.c b/drivers/acpi/pfr_update.c
>  > index 6283105bb0e8..0219347cd78f 100644
>  > --- a/drivers/acpi/pfr_update.c
>  > +++ b/drivers/acpi/pfr_update.c
>  > @@ -161,24 +161,28 @@ static int query_capability(struct pfru_update_cap_info *cap_hdr,
>  >      cap_hdr->update_cap = out_obj->package.elements[CAP_UPDATE_IDX].integer.value;
>  >      memcpy(&cap_hdr->code_type,
>  >             out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.pointer,
>  > -           out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.length);
>  > +           min_t(u32, out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.length,
>  > +             sizeof(cap_hdr->code_type)));
>  >      cap_hdr->fw_version =
>  >          out_obj->package.elements[CAP_FW_VER_IDX].integer.value;
>  >      cap_hdr->code_rt_version =
>  >          out_obj->package.elements[CAP_CODE_RT_VER_IDX].integer.value;
>  >      memcpy(&cap_hdr->drv_type,
>  >             out_obj->package.elements[CAP_DRV_TYPE_IDX].buffer.pointer,
>  > -           out_obj->package.elements[CAP_DRV_TYPE_IDX].buffer.length);
>  > +           min_t(u32, out_obj->package.elements[CAP_DRV_TYPE_IDX].buffer.length,
>  > +             sizeof(cap_hdr->drv_type)));
>  >      cap_hdr->drv_rt_version =
>  >          out_obj->package.elements[CAP_DRV_RT_VER_IDX].integer.value;
>  >      cap_hdr->drv_svn =
>  >          out_obj->package.elements[CAP_DRV_SVN_IDX].integer.value;
>  >      memcpy(&cap_hdr->platform_id,
>  >             out_obj->package.elements[CAP_PLAT_ID_IDX].buffer.pointer,
>  > -           out_obj->package.elements[CAP_PLAT_ID_IDX].buffer.length);
>  > +           min_t(u32, out_obj->package.elements[CAP_PLAT_ID_IDX].buffer.length,
>  > +             sizeof(cap_hdr->platform_id)));
>  >      memcpy(&cap_hdr->oem_id,
>  >             out_obj->package.elements[CAP_OEM_ID_IDX].buffer.pointer,
>  > -           out_obj->package.elements[CAP_OEM_ID_IDX].buffer.length);
>  > +           min_t(u32, out_obj->package.elements[CAP_OEM_ID_IDX].buffer.length,
>  > +             sizeof(cap_hdr->oem_id)));
>  >      cap_hdr->oem_info_len =
>  >          out_obj->package.elements[CAP_OEM_INFO_IDX].buffer.length;
>  >
>  > --
>  > 2.55.0
>  >
>
>