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Subject: Re: [PATCH] ACPI: scan: Fix a Hyper-V Linux VM panic caused by buffer
 overflow
To:     decui@microsoft.com, linux-acpi@vger.kernel.org, rjw@rjwysocki.net,
        len.brown@intel.com, mikelley@microsoft.com
Cc:     linux-kernel@vger.kernel.org, wei.liu@kernel.org,
        sthemmin@microsoft.com, haiyangz@microsoft.com, kys@microsoft.com
References: <20201218040826.57203-1-decui@microsoft.com>
From:   Dwaipayan Ray <dwaipayanray1@gmail.com>
Message-ID: <42a039e8-d31e-9f17-bfe6-6a50968688db@gmail.com>
Date:   Thu, 7 Jan 2021 19:09:53 +0530
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On 18/12/20 9:38 am, Dexuan Cui wrote:
> 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@microsoft.com>
> ---
>   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));

Please prefer strscpy() over strlcpy():

+		strscpy(acpi_device_bus_id->bus_id, acpi_device_hid(device),
+			sizeof(acpi_device_bus_id->bus_id));

See: 
https://lore.kernel.org/lkml/CAHk-=wgfRnXz0W3D37d01q3JFkr_i_uTL=V6A6G1oUZcprmknw@mail.gmail.com/

Thanks,
Dwaipayan.

>   		acpi_device_bus_id->instance_no = 0;
>   		list_add_tail(&acpi_device_bus_id->node, &acpi_bus_id_list);
>   	}