linux-kernel - Re: [PATCH v2 1/2] i2c: core-smbus: fix a potential uninitialization bug

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Message-ID: <20180510111737.b6g7s2nnf6froote@ninjato>
Date:   Thu, 10 May 2018 13:17:37 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Wenwen Wang <wang6495@....edu>
Cc:     Kangjie Lu <kjlu@....edu>,
        "open list:I2C SUBSYSTEM" <linux-i2c@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] i2c: core-smbus: fix a potential uninitialization
 bug

On Sat, May 05, 2018 at 07:57:10AM -0500, Wenwen Wang wrote:
> In i2c_smbus_xfer_emulated(), there are two buffers: msgbuf0 and msgbuf1,
> which are used to save a series of messages, as mentioned in the comment.
> According to the value of the variable 'size', msgbuf0 is initialized to
> various values. In contrast, msgbuf1 is left uninitialized until the
> function i2c_transfer() is invoked. However, msgbuf1 is not always
> initialized on all possible execution paths (implementation) of
> i2c_transfer(). Thus, it is possible that msgbuf1 may still be
> uninitialized even after the invocation of the function i2c_transfer(),
> especially when the return value of ic2_transfer() is not checked properly.
> In the following execution, the uninitialized msgbuf1 will be used, such as
> for security checks. Since uninitialized values can be random and
> arbitrary, this will cause undefined behaviors or even check bypass. For
> example, it is expected that if the value of 'size' is
> I2C_SMBUS_BLOCK_PROC_CALL, the value of data->block[0] should not be larger
> than I2C_SMBUS_BLOCK_MAX. But, at the end of i2c_smbus_xfer_emulated(), the
> value read from msgbuf1 is assigned to data->block[0], which can
> potentially lead to invalid block write size, as demonstrated in the error
> message.
> 
> This patch initializes the first byte of msgbuf1 with 0 to avoid such
> undefined behaviors or security issues.
> 
> Signed-off-by: Wenwen Wang <wang6495@....edu>

From what I can tell, this patch is not needed anymore after patch 2 is
applied. Correct?


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