RE: [PATCH] ACPI: scan: Fix a Hyper-V Linux VM panic caused by buffer overflow

[Michael Kelley]

From: Dexuan Cui <decui@xxxxxxxxxxxxx> Sent: Thursday, December 17, 2020 8:08 PM
> 
> Linux VM on Hyper-V crashes with the latest mainline:
> 
> [    4.069624] detected buffer overflow in strcpy
> [    4.077733] kernel BUG at lib/string.c:1149!
> ..
> [    4.085819] RIP: 0010:fortify_panic+0xf/0x11
> ...
> [    4.085819] Call Trace:
> [    4.085819]  acpi_device_add.cold.15+0xf2/0xfb
> [    4.085819]  acpi_add_single_object+0x2a6/0x690
> [    4.085819]  acpi_bus_check_add+0xc6/0x280
> [    4.085819]  acpi_ns_walk_namespace+0xda/0x1aa
> [    4.085819]  acpi_walk_namespace+0x9a/0xc2
> [    4.085819]  acpi_bus_scan+0x78/0x90
> [    4.085819]  acpi_scan_init+0xfa/0x248
> [    4.085819]  acpi_init+0x2c1/0x321
> [    4.085819]  do_one_initcall+0x44/0x1d0
> [    4.085819]  kernel_init_freeable+0x1ab/0x1f4
> 
> This is because of the recent buffer overflow detection in the
> commit 6a39e62abbaf ("lib: string.h: detect intra-object overflow in fortified string
> functions")
> 
> Here acpi_device_bus_id->bus_id can only hold 14 characters, while the
> the acpi_device_hid(device) returns a 22-char string
> "HYPER_V_GEN_COUNTER_V1".
> 
> Per ACPI Spec v6.2, Section 6.1.5 _HID (Hardware ID), if the ID is a
> string, it must be of the form AAA#### or NNNN####, i.e. 7 chars or 8
> chars.
> 
> The field bus_id in struct acpi_device_bus_id was originally defined as
> char bus_id[9], and later was enlarged to char bus_id[15] in 2007 in the
> commit bb0958544f3c ("ACPI: use more understandable bus_id for ACPI devices")
> 
> It looks like so far an ID string of >=15 chars is only seen in the guest
> BIOS/firmware by Hyper-V, and AFAIK the ID string "HYPER_V_GEN_COUNTER_V1"
> is never used by Linux VM on Hyper-V, so let's just truncate the string to
> fix the panic.
> 
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> ---
>  drivers/acpi/scan.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index a1b226eb2ce2..b801442b6b1b 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -674,7 +674,8 @@ int acpi_device_add(struct acpi_device *device,
>  	}
>  	if (!found) {
>  		acpi_device_bus_id = new_bus_id;
> -		strcpy(acpi_device_bus_id->bus_id, acpi_device_hid(device));
> +		strlcpy(acpi_device_bus_id->bus_id, acpi_device_hid(device),
> +			sizeof(acpi_device_bus_id->bus_id));
>  		acpi_device_bus_id->instance_no = 0;
>  		list_add_tail(&acpi_device_bus_id->node, &acpi_bus_id_list);
>  	}
> --
> 2.19.1

Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>