Re: [PATCH] evm: fix writing <securityfs>/evm overflow

[Stefan Berger]

On 4/29/21 3:53 PM, Mimi Zohar wrote:
> EVM_SETUP_COMPLETE is defined as 0x80000000, which is larger than INT_MAX.
> The "-fno-strict-overflow" compiler option properly prevents signaling
> EVM that the EVM policy setup is complete.  Define and read an unsigned
> int.
>
> Fixes: f00d79750712 ("EVM: Allow userspace to signal an RSA key has been
> loaded")
> Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>


Tested-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>

> ---
>   security/integrity/evm/evm_secfs.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
> index bbc85637e18b..0007d3362754 100644
> --- a/security/integrity/evm/evm_secfs.c
> +++ b/security/integrity/evm/evm_secfs.c
> @@ -66,12 +66,13 @@ static ssize_t evm_read_key(struct file *filp, char __user *buf,
>   static ssize_t evm_write_key(struct file *file, const char __user *buf,
>   			     size_t count, loff_t *ppos)
>   {
> -	int i, ret;
> +	unsigned int i;
> +	int ret;
>   
>   	if (!capable(CAP_SYS_ADMIN) || (evm_initialized & EVM_SETUP_COMPLETE))
>   		return -EPERM;
>   
> -	ret = kstrtoint_from_user(buf, count, 0, &i);
> +	ret = kstrtouint_from_user(buf, count, 0, &i);
>   
>   	if (ret)
>   		return ret;