linux-kernel - [PATCH v2] efi: Fix memory leak in efivar_ssdt

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Message-ID: <Zyi6g8W0OqKcng6S@grain>
Date: Mon, 4 Nov 2024 15:13:55 +0300
From: Cyrill Gorcunov <gorcunov@...il.com>
To: LKML <linux-kernel@...r.kernel.org>, linux-efi@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>
Subject: [PATCH v2] efi: Fix memory leak in efivar_ssdt_load

When we load ssdt from efi variable (specified with efivar_ssdt=something
boot command line argument) a name for the variable is allocated
dynamically because we traverse all efi variables. Unlike an acpi table
data, which is later used by acpi engine, the name is no longer needed
once traverse is complete -- don't forget to free this memory.

Same time we silently ignore any errors happened here lets print
a message if something went wrong (but do not exit since this is
not a critical error and the system should continue to boot).

Also while here -- add a note why we keep ssdt table on success.

Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>
Cc: Ard Biesheuvel <ardb@...nel.org>
---
It is still unclear for me why we don't exit with error if acpi_load_table
failed but continue to iterate keys and don't report a caller with error
instead. I didn't change this logic for backward compatibility sake but
still looks suspicious.

 drivers/firmware/efi/efi.c |   41 ++++++++++++++++++++++++++++-------------
 1 file changed, 28 insertions(+), 13 deletions(-)

Index: linux-tip.git/drivers/firmware/efi/efi.c
===================================================================
--- linux-tip.git.orig/drivers/firmware/efi/efi.c
+++ linux-tip.git/drivers/firmware/efi/efi.c
@@ -273,6 +273,7 @@ static __init int efivar_ssdt_load(void)
 	efi_char16_t *name = NULL;
 	efi_status_t status;
 	efi_guid_t guid;
+	int ret = 0;
 
 	if (!efivar_ssdt[0])
 		return 0;
@@ -294,8 +295,8 @@ static __init int efivar_ssdt_load(void)
 			efi_char16_t *name_tmp =
 				krealloc(name, name_size, GFP_KERNEL);
 			if (!name_tmp) {
-				kfree(name);
-				return -ENOMEM;
+				ret = -ENOMEM;
+				goto out;
 			}
 			name = name_tmp;
 			continue;
@@ -309,26 +310,38 @@ static __init int efivar_ssdt_load(void)
 		pr_info("loading SSDT from variable %s-%pUl\n", efivar_ssdt, &guid);
 
 		status = efi.get_variable(name, &guid, NULL, &data_size, NULL);
-		if (status != EFI_BUFFER_TOO_SMALL || !data_size)
-			return -EIO;
+		if (status != EFI_BUFFER_TOO_SMALL || !data_size) {
+			ret = -EIO;
+			goto out;
+		}
 
 		data = kmalloc(data_size, GFP_KERNEL);
-		if (!data)
-			return -ENOMEM;
+		if (!data) {
+			ret = -ENOMEM;
+			goto out;
+		}
 
 		status = efi.get_variable(name, &guid, NULL, &data_size, data);
 		if (status == EFI_SUCCESS) {
-			acpi_status ret = acpi_load_table(data, NULL);
-			if (ret)
-				pr_err("failed to load table: %u\n", ret);
-			else
+			acpi_status acpi_ret = acpi_load_table(data, NULL);
+			if (ACPI_FAILURE(acpi_ret)) {
+				pr_err("efivar_ssdt: failed to load table: %u\n",
+				       acpi_ret);
+			} else {
+				/*
+				 * The @data will be in use by ACPI engine,
+				 * do not free it!
+				 */
 				continue;
+			}
 		} else {
-			pr_err("failed to get var data: 0x%lx\n", status);
+			pr_err("efivar_ssdt: failed to get var data: 0x%lx\n", status);
 		}
 		kfree(data);
 	}
-	return 0;
+out:
+	kfree(name);
+	return ret;
 }
 #else
 static inline int efivar_ssdt_load(void) { return 0; }
@@ -433,7 +446,9 @@ static int __init efisubsys_init(void)
 		error = generic_ops_register();
 		if (error)
 			goto err_put;
-		efivar_ssdt_load();
+		error = efivar_ssdt_load();
+		if (error)
+			pr_err("efi: failed to load SSDT, error %d.\n", error);
 		platform_device_register_simple("efivars", 0, NULL, 0);
 	}