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

[Kees Cook]

subject typo: "sysclt" -> "sysctl"

On Thu, Dec 24, 2020 at 03:42:56PM +0800, 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".
> 
> log:
> 	Kernel command line: .... hung_task_panic
> 	....
> 	[000000000000000n] user address but active_mm is swapper
> 	Internal error: Oops: 96000005 [#1] SMP
> 	Modules linked in:
> 	CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.10.1 #1
> 	Hardware name: linux,dummy-virt (DT)
> 	pstate: 40000005 (nZcv daif -PAN -UAO -TCO BTYPE=--)
> 	pc : __pi_strlen+0x10/0x98
> 	lr : process_sysctl_arg+0x1e4/0x2ac
> 	sp : ffffffc01104bd40
> 	x29: ffffffc01104bd40 x28: 0000000000000000
> 	x27: ffffff80c0a4691e x26: ffffffc0102a7c8c
> 	x25: 0000000000000000 x24: ffffffc01104be80
> 	x23: ffffff80c22f0b00 x22: ffffff80c02e28c0
> 	x21: ffffffc0109f9000 x20: 0000000000000000
> 	x19: ffffffc0107c08de x18: 0000000000000003
> 	x17: ffffffc01105d000 x16: 0000000000000054
> 	x15: ffffffffffffffff x14: 3030253078413830
> 	x13: 000000000000ffff x12: 0000000000000000
> 	x11: 0101010101010101 x10: 0000000000000005
> 	x9 : 0000000000000003 x8 : ffffff80c0980c08
> 	x7 : 0000000000000000 x6 : 0000000000000002
> 	x5 : ffffff80c0235000 x4 : ffffff810f7c7ee0
> 	x3 : 000000000000043a x2 : 00bdcc4ebacf1a54
> 	x1 : 0000000000000000 x0 : 0000000000000000
> 	Call trace:
> 	 __pi_strlen+0x10/0x98
> 	 parse_args+0x278/0x344
> 	 do_sysctl_args+0x8c/0xfc
> 	 kernel_init+0x5c/0xf4
> 	 ret_from_fork+0x10/0x30
> 	Code: b200c3eb 927cec01 f2400c07 54000301 (a8c10c22)
> 
> Fixes: 3db978d480e2843 ("kernel/sysctl: support setting sysctl parameters
>  from kernel command line")
> Signed-off-by: Xiaoming Ni <nixiaoming@xxxxxxxxxx>
> ---
>  fs/proc/proc_sysctl.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 317899222d7f..4516411a2b44 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -1757,6 +1757,9 @@ static int process_sysctl_arg(char *param, char *val,
>  	loff_t pos = 0;
>  	ssize_t wret;
>  
> +	if (!val)
> +		return 0;
> +
>  	if (strncmp(param, "sysctl", sizeof("sysctl") - 1) == 0) {
>  		param += sizeof("sysctl") - 1;

Otherwise, yeah, this is a good test to add. I would make it more
verbose, though:

	if (!val) {
		pr_err("Missing param value! Expected '%s=...value...'\n", param);
		return 0;
	}

-- 
Kees Cook