On Fri 08-01-21 10:33:39, 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>
Thanks for catching this!
> ---------
> v2:
> 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 | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 317899222d7f..dc1a56515e86 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -1757,6 +1757,11 @@ static int process_sysctl_arg(char *param, char *val,
> loff_t pos = 0;
> ssize_t wret;
>
> + if (!val) {
> + pr_err("Missing param value! Expected '%s=...value...'\n", param);
> + return 0;
> + }
Shouldn't you return an error here? Also my understanding is that
parse_args is responsible for reporting the error.
> +
> if (strncmp(param, "sysctl", sizeof("sysctl") - 1) == 0) {
> param += sizeof("sysctl") - 1;
>
> --
> 2.27.0
--
Michal Hocko
SUSE Labs
