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;
>
