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SubjectRe: [PATCH] i2c: core-smbus: fix a potential uninitialization bug
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On 2018-05-05 03:43, 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, mgsbuf1 is not always
> initialized on all possible execution paths (implementation) of
> i2c_transfer(). Thus, it is possible that mgsbuf1 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 checks the return value of i2c_transfer() and also initializes
> the first byte of msgbuf1 with 0 to avoid undefined behaviors or security
> issues.
>
> Signed-off-by: Wenwen Wang <wang6495@umn.edu>
> ---
> drivers/i2c/i2c-core-smbus.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
> index b5aec33..e8470d5 100644
> --- a/drivers/i2c/i2c-core-smbus.c
> +++ b/drivers/i2c/i2c-core-smbus.c
> @@ -344,6 +344,7 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
> };
>
> msgbuf0[0] = command;
> + msgbug1[0] = 0;
> switch (size) {
> case I2C_SMBUS_QUICK:
> msg[0].len = 0;
> @@ -466,6 +467,8 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
> status = i2c_transfer(adapter, msg, num);
> if (status < 0)
> return status;
> + if (status != num)
> + return -EIO;
>
> /* Check PEC if last message is a read */
> if (i && (msg[num-1].flags & I2C_M_RD)) {
>

I think these two hunks should be two separate patches. They address
orthogonal issues...

Cheers,
Peter

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