Re: [PATCH v2] platform/x86: intel_pmc_core: Uninitialized data in pmc_core_lpm_latch_mode_write()

Hans de Goede
2021-04-21T19:32:26Z

Hi,

On 4/21/21 5:19 PM, Dan Carpenter wrote:
> The simple_write_to_buffer() can return success if even a single byte
> is copied from user space. In this case it can result in using
> uninitalized data if the buf[] array is not fully initialized. Really
> we should only succeed if the whole buffer is copied.
>
> Just using copy_from_user() is simpler and more appropriate.
>
> Fixes: 8074a79fad2e ("platform/x86: intel_pmc_core: Add option to set/clear LPM mode")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> v2: The first version of this patch returned -EINVAL if userspace didn't
> give us NUL terminated strings. That's not necessarily a good
> assumption.
>
> This patch is just simpler as well. No need to introduce the "len"
> variable because "count" is capped at the start of the function.

Much better, thank you.

Thank you for your patch, I've applied this patch to my review-hans
branch:
https://git.kernel.org/pub/scm/linux/kernel/git/pdx86/platform-drivers-x86.git/log/?h=review-hans

Note it will show up in my review-hans branch once I've pushed my
local branch there, which might take a while.

Once I've run some tests on this branch the patches there will be
added to the platform-drivers-x86/for-next branch and eventually
will be included in the pdx86 pull-request to Linus for the next
merge-window.

Regards,

Hans

> drivers/platform/x86/intel_pmc_core.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/platform/x86/intel_pmc_core.c b/drivers/platform/x86/intel_pmc_core.c
> index d174aeb492e0..b0e486a6bdfb 100644
> --- a/drivers/platform/x86/intel_pmc_core.c
> +++ b/drivers/platform/x86/intel_pmc_core.c
> @@ -1360,17 +1360,13 @@ static ssize_t pmc_core_lpm_latch_mode_write(struct file *file,
> struct pmc_dev *pmcdev = s->private;
> bool clear = false, c10 = false;
> unsigned char buf[8];
> - ssize_t ret;
> int idx, m, mode;
> u32 reg;
>
> if (count > sizeof(buf) - 1)
> return -EINVAL;
> -
> - ret = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, userbuf, count);
> - if (ret < 0)
> - return ret;
> -
> + if (copy_from_user(buf, userbuf, count))
> + return -EFAULT;
> buf[count] = '\0';
>
> /*
>