linux-kernel - [PATCH][next] nvmem: core: Fix unintentional sign extension issue

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Message-Id: <20210311095316.6480-1-colin.king@canonical.com>
Date:   Thu, 11 Mar 2021 09:53:16 +0000
From:   Colin King <colin.king@...onical.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Douglas Anderson <dianders@...omium.org>,
        linux-kernel@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org
Subject: [PATCH][next] nvmem: core: Fix unintentional sign extension issue

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

The shifting of the u8 integer buf[3] by 24 bits to the left will
be promoted to a 32 bit signed int and then sign-extended to a
u64. In the event that the top bit of buf[3] is set then all
then all the upper 32 bits of the u64 end up as also being set
because of the sign-extension. Fix this by casting buf[i] to
a u64 before the shift.

Addresses-Coverity: ("Unintended sign extension")
Fixes: 097eb1136ebb ("nvmem: core: Add functions to make number reading easy")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/nvmem/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 635e3131eb5f..bca671ff4e54 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -1693,7 +1693,7 @@ int nvmem_cell_read_variable_le_u64(struct device *dev, const char *cell_id,
 	/* Copy w/ implicit endian conversion */
 	*val = 0;
 	for (i = 0; i < len; i++)
-		*val |= buf[i] << (8 * i);
+		*val |= (uint64_t)buf[i] << (8 * i);
 
 	kfree(buf);
 
-- 
2.30.2