linux-kernel - [PATCH] PNP: fix unintended sign extension on left shifts

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Message-Id: <20191014131608.31335-1-colin.king@canonical.com>
Date:   Mon, 14 Oct 2019 14:16:08 +0100
From:   Colin King <colin.king@...onical.com>
To:     Jaroslav Kysela <perex@...ex.cz>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] PNP: fix unintended sign extension on left shifts

From: Colin Ian King <colin.king@...onical.com>

Shifting a u8 left will cause the value to be promoted to an integer. If
the top bit of the u8 is set then the following conversion to a 64 bit
resource_size_t will sign extend the value causing the upper 32 bits
to be set in the result.

Fix this by casting the u8 value to a resource_size_t before the shift.
Original commit is pre-git history.

Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/pnp/isapnp/core.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/pnp/isapnp/core.c b/drivers/pnp/isapnp/core.c
index 179b737280e1..c947b1673041 100644
--- a/drivers/pnp/isapnp/core.c
+++ b/drivers/pnp/isapnp/core.c
@@ -511,10 +511,14 @@ static void __init isapnp_parse_mem32_resource(struct pnp_dev *dev,
 	unsigned char flags;
 
 	isapnp_peek(tmp, size);
-	min = (tmp[4] << 24) | (tmp[3] << 16) | (tmp[2] << 8) | tmp[1];
-	max = (tmp[8] << 24) | (tmp[7] << 16) | (tmp[6] << 8) | tmp[5];
-	align = (tmp[12] << 24) | (tmp[11] << 16) | (tmp[10] << 8) | tmp[9];
-	len = (tmp[16] << 24) | (tmp[15] << 16) | (tmp[14] << 8) | tmp[13];
+	min = ((resource_size_t)tmp[4] << 24) | (tmp[3] << 16) |
+              (tmp[2] << 8) | tmp[1];
+	max = ((resource_size_t)tmp[8] << 24) | (tmp[7] << 16) |
+              (tmp[6] << 8) | tmp[5];
+	align = ((resource_size_t)tmp[12] << 24) | (tmp[11] << 16) |
+              (tmp[10] << 8) | tmp[9];
+	len = ((resource_size_t)tmp[16] << 24) | (tmp[15] << 16) |
+              (tmp[14] << 8) | tmp[13];
 	flags = tmp[0];
 	pnp_register_mem_resource(dev, option_flags,
 				  min, max, align, len, flags);
@@ -532,8 +536,10 @@ static void __init isapnp_parse_fixed_mem32_resource(struct pnp_dev *dev,
 	unsigned char flags;
 
 	isapnp_peek(tmp, size);
-	base = (tmp[4] << 24) | (tmp[3] << 16) | (tmp[2] << 8) | tmp[1];
-	len = (tmp[8] << 24) | (tmp[7] << 16) | (tmp[6] << 8) | tmp[5];
+	base = ((resource_size_t)tmp[4] << 24) | (tmp[3] << 16) |
+	       (tmp[2] << 8) | tmp[1];
+	len = ((resource_size_t)tmp[8] << 24) | (tmp[7] << 16) |
+              (tmp[6] << 8) | tmp[5];
 	flags = tmp[0];
 	pnp_register_mem_resource(dev, option_flags, base, base, 0, len, flags);
 }
-- 
2.20.1