linux-kernel - [PATCH 1/4] ACPI: sysfs: Fix the check for a potential string truncation

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Message-Id: <20001867d5d19c3b3e677f6020750cc232b3325b.1698081019.git.christophe.jaillet@wanadoo.fr>
Date:   Mon, 23 Oct 2023 20:32:54 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     rafael@...nel.org, lenb@...nel.org
Cc:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: [PATCH 1/4] ACPI: sysfs: Fix the check for a potential string truncation

snprintf() does not return negative values on error.
To know if the buffer was too small, the returned value should be compared
with the length of the passed buffer. If it is bigger or equal, then the
output has been truncated.

Update the test for truncation accordingly.

Also return -ENOMEM in such a case, as already done below in the same
functions.

Fixes: 8765c5ba1949 ("ACPI / scan: Rework modalias creation when "compatible" is present")
Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
 drivers/acpi/device_sysfs.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/device_sysfs.c b/drivers/acpi/device_sysfs.c
index 9d8e90744cb5..4deb36dccb73 100644
--- a/drivers/acpi/device_sysfs.c
+++ b/drivers/acpi/device_sysfs.c
@@ -158,8 +158,8 @@ static int create_pnp_modalias(const struct acpi_device *acpi_dev, char *modalia
 		return 0;
 
 	len = snprintf(modalias, size, "acpi:");
-	if (len <= 0)
-		return len;
+	if (len >= size)
+		return -ENOMEM;
 
 	size -= len;
 
@@ -212,8 +212,8 @@ static int create_of_modalias(const struct acpi_device *acpi_dev, char *modalias
 	len = snprintf(modalias, size, "of:N%sT", (char *)buf.pointer);
 	ACPI_FREE(buf.pointer);
 
-	if (len <= 0)
-		return len;
+	if (len >= size)
+		return -ENOMEM;
 
 	of_compatible = acpi_dev->data.of_compatible;
 	if (of_compatible->type == ACPI_TYPE_PACKAGE) {
-- 
2.32.0