[PATCH 4.19 07/66] firmware: dmi: Stop decoding on broken entry

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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jean Delvare <jdelvare@xxxxxxx>

[ Upstream commit 0ef11f604503b1862a21597436283f158114d77e ]

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 <jdelvare@xxxxxxx>
Link: https://lore.kernel.org/linux-kernel/Zh2K3-HLXOesT_vZ@liuwe-devbox-debian-v2/T/
Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/firmware/dmi_scan.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
index 0dc0c78f1fdb2..311c396bdda7d 100644
--- a/drivers/firmware/dmi_scan.c
+++ b/drivers/firmware/dmi_scan.c
@@ -95,6 +95,17 @@ static void dmi_decode_table(u8 *buf,
 	       (data - buf + sizeof(struct dmi_header)) <= dmi_len) {
 		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 %zd (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
-- 
2.43.0







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