Re: [PATCH v4] proc_sysctl: fix oops caused by incorrect command parameters.

[Vlastimil Babka]

On 1/18/21 2:30 PM, Xiaoming Ni wrote:
> The process_sysctl_arg() does not check whether val is empty before
>  invoking strlen(val). If the command line parameter () is incorrectly
>  configured and val is empty, oops is triggered.
> 
> For example:
>   "hung_task_panic=1" is incorrectly written as "hung_task_panic", oops is
>   triggered. The call stack is as follows:
>     Kernel command line: .... hung_task_panic
>     ......
>     Call trace:
>     __pi_strlen+0x10/0x98
>     parse_args+0x278/0x344
>     do_sysctl_args+0x8c/0xfc
>     kernel_init+0x5c/0xf4
>     ret_from_fork+0x10/0x30
> 
> To fix it, check whether "val" is empty when "phram" is a sysctl field.
> Error codes are returned in the failure branch, and error logs are
> generated by parse_args().
> 
> Fixes: 3db978d480e2843 ("kernel/sysctl: support setting sysctl parameters
>  from kernel command line")
> Cc: stable@xxxxxxxxxx # v5.8-rc1+
> Signed-off-by: Xiaoming Ni <nixiaoming@xxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Thanks!

> 
> ---------
> v4: According to Vlastimil Babka's recommendations
>   add check len == 0, and cc stable
> v3: https://lore.kernel.org/lkml/20210112033155.91502-1-nixiaoming@xxxxxxxxxx/
>   Return -EINVAL, When phram is the sysctl field and val is empty.
> 
> v2: https://lore.kernel.org/lkml/20210108023339.55917-1-nixiaoming@xxxxxxxxxx/
>   Added log output of the failure branch based on the review comments of Kees Cook.
> 
> v1: https://lore.kernel.org/lkml/20201224074256.117413-1-nixiaoming@xxxxxxxxxx/
> 
> ---------
> ---
>  fs/proc/proc_sysctl.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 317899222d7f..d2018f70d1fa 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -1770,6 +1770,12 @@ static int process_sysctl_arg(char *param, char *val,
>  			return 0;
>  	}
>  
> +	if (!val)
> +		return -EINVAL;
> +	len = strlen(val);
> +	if (len == 0)
> +		return -EINVAL;
> +
>  	/*
>  	 * To set sysctl options, we use a temporary mount of proc, look up the
>  	 * respective sys/ file and write to it. To avoid mounting it when no
> @@ -1811,7 +1817,6 @@ static int process_sysctl_arg(char *param, char *val,
>  				file, param, val);
>  		goto out;
>  	}
> -	len = strlen(val);
>  	wret = kernel_write(file, val, len, &pos);
>  	if (wret < 0) {
>  		err = wret;
>