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    Subject[PATCH 4.4 45/68] platform/chrome: cros_ec_dev - double fetch bug in ioctl
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Dan Carpenter <dan.carpenter@oracle.com>

    commit 096cdc6f52225835ff503f987a0d68ef770bb78e upstream.

    We verify "u_cmd.outsize" and "u_cmd.insize" but we need to make sure
    that those values have not changed between the two copy_from_user()
    calls. Otherwise it could lead to a buffer overflow.

    Additionally, cros_ec_cmd_xfer() can set s_cmd->insize to a lower value.
    We should use the new smaller value so we don't copy too much data to
    the user.

    Reported-by: Pengfei Wang <wpengfeinudt@gmail.com>
    Fixes: a841178445bb ('mfd: cros_ec: Use a zero-length array for command data')
    Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
    Reviewed-by: Kees Cook <keescook@chromium.org>
    Tested-by: Gwendal Grignou <gwendal@chromium.org>
    Signed-off-by: Olof Johansson <olof@lixom.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/platform/chrome/cros_ec_dev.c | 8 +++++++-
    1 file changed, 7 insertions(+), 1 deletion(-)

    --- a/drivers/platform/chrome/cros_ec_dev.c
    +++ b/drivers/platform/chrome/cros_ec_dev.c
    @@ -147,13 +147,19 @@ static long ec_device_ioctl_xcmd(struct
    goto exit;
    }

    + if (u_cmd.outsize != s_cmd->outsize ||
    + u_cmd.insize != s_cmd->insize) {
    + ret = -EINVAL;
    + goto exit;
    + }
    +
    s_cmd->command += ec->cmd_offset;
    ret = cros_ec_cmd_xfer(ec->ec_dev, s_cmd);
    /* Only copy data to userland if data was received. */
    if (ret < 0)
    goto exit;

    - if (copy_to_user(arg, s_cmd, sizeof(*s_cmd) + u_cmd.insize))
    + if (copy_to_user(arg, s_cmd, sizeof(*s_cmd) + s_cmd->insize))
    ret = -EFAULT;
    exit:
    kfree(s_cmd);

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