linux-kernel - [PATCH] eeprom: ee1004: limit i2c reads to I2C_SMBUS_BLOCK

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Message-Id: <20220203165024.47767-1-jonas@protocubo.io>
Date:   Thu,  3 Feb 2022 13:49:52 -0300
From:   Jonas Malaco <jonas@...tocubo.io>
To:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jonas Malaco <jonas@...tocubo.io>, stable@...r.kernel.org,
        Heiner Kallweit <hkallweit1@...il.com>,
        Wolfram Sang <wsa@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] eeprom: ee1004: limit i2c reads to I2C_SMBUS_BLOCK_MAX

Commit effa453168a7 ("i2c: i801: Don't silently correct invalid transfer
size") revealed that ee1004_eeprom_read() did not properly limit how
many bytes to read at once.

In particular, i2c_smbus_read_i2c_block_data_or_emulated() takes the
length to read as an u8.  If count == 256 after taking into account the
offset and page boundary, the cast to u8 overflows.  And this is common
when user space tries to read the entire EEPROM at once.

To fix it, limit each read to I2C_SMBUS_BLOCK_MAX (32) bytes, already
the maximum length i2c_smbus_read_i2c_block_data_or_emulated() allows.

Fixes: effa453168a7 ("i2c: i801: Don't silently correct invalid transfer size")
Cc: stable@...r.kernel.org
Signed-off-by: Jonas Malaco <jonas@...tocubo.io>
---
 drivers/misc/eeprom/ee1004.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/misc/eeprom/ee1004.c b/drivers/misc/eeprom/ee1004.c
index bb9c4512c968..9fbfe784d710 100644
--- a/drivers/misc/eeprom/ee1004.c
+++ b/drivers/misc/eeprom/ee1004.c
@@ -114,6 +114,9 @@ static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
 	if (offset + count > EE1004_PAGE_SIZE)
 		count = EE1004_PAGE_SIZE - offset;

+	if (count > I2C_SMBUS_BLOCK_MAX)
+		count = I2C_SMBUS_BLOCK_MAX;
+
 	return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
 }

base-commit: 88808fbbead481aedb46640a5ace69c58287f56a
-- 
2.35.1