2024-04-18 12:27:51

by Jean Delvare

Subject: [PATCH v2] firmware: dmi: Stop decoding on broken entry

If a DMI table entry is shorter than 4 bytes, it is invalid. Due to
how DMI table parsing works, it is impossible to safely recover from
such an error, so we have to stop decoding the table.

Signed-off-by: Jean Delvare <[email protected]>
Reported-by: Michael Schierl <[email protected]>
Link: https://lore.kernel.org/linux-kernel/Zh2K3-HLXOesT_vZ@liuwe-devbox-debian-v2/T/
Tested-by: Michael Schierl <[email protected]>
---
Changes since v1:
* Also log the offset of the corrupted entry (suggested by Michael Kelley)

drivers/firmware/dmi_scan.c | 11 +++++++++++
1 file changed, 11 insertions(+)

--- linux-6.8.orig/drivers/firmware/dmi_scan.c
+++ linux-6.8/drivers/firmware/dmi_scan.c
@@ -102,6 +102,17 @@ static void dmi_decode_table(u8 *buf,
const struct dmi_header *dm = (const struct dmi_header *)data;

/*
+ * If a short entry is found (less than 4 bytes), not only it
+ * is invalid, but we cannot reliably locate the next entry.
+ */
+ if (dm->length < sizeof(struct dmi_header)) {
+ pr_warn(FW_BUG
+ "Corrupted DMI table, offset %ld (only %d entries processed)\n",
+ data - buf, i);
+ break;
+ }
+
+ /*
* We want to know the total length (formatted area and
* strings) before decoding to make sure we won't run off the
* table in dmi_decode or dmi_string


--
Jean Delvare
SUSE L3 Support

2024-04-18 13:58:05

by Michael Kelley

Subject: RE: [PATCH v2] firmware: dmi: Stop decoding on broken entry

From: Jean Delvare <[email protected]> Sent: Thursday, April 18, 2024 5:28 AM
>
> If a DMI table entry is shorter than 4 bytes, it is invalid. Due to
> how DMI table parsing works, it is impossible to safely recover from
> such an error, so we have to stop decoding the table.
>
> Signed-off-by: Jean Delvare <[email protected]>
> Reported-by: Michael Schierl <[email protected]>
> Link: https://lore.kernel.org/linux-kernel/Zh2K3-HLXOesT_vZ@liuwe-devbox-debian-v2/T/
> Tested-by: Michael Schierl <[email protected]>
> ---
> Changes since v1:
> * Also log the offset of the corrupted entry (suggested by Michael Kelley)
>
> drivers/firmware/dmi_scan.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> --- linux-6.8.orig/drivers/firmware/dmi_scan.c
> +++ linux-6.8/drivers/firmware/dmi_scan.c
> @@ -102,6 +102,17 @@ static void dmi_decode_table(u8 *buf,
> const struct dmi_header *dm = (const struct dmi_header *)data;
>
> /*
> + * If a short entry is found (less than 4 bytes), not only it
> + * is invalid, but we cannot reliably locate the next entry.
> + */
> + if (dm->length < sizeof(struct dmi_header)) {
> + pr_warn(FW_BUG
> + "Corrupted DMI table, offset %ld (only %d entries processed)\n",
> + data - buf, i);
> + break;
> + }
> +
> + /*
> * We want to know the total length (formatted area and
> * strings) before decoding to make sure we won't run off the
> * table in dmi_decode or dmi_string
>

Reviewed-by: Michael Kelley <[email protected]>