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SubjectRe: [PATCH v2] proc_sysctl: fix oops caused by incorrect command parameters.
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On 2021/1/8 17:21, Michal Hocko wrote:
> 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@huawei.com>
>
> 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@huawei.com/
>> ---------
>> ---
>> 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;
I may need to move the validation code for val to the end of the
validation code for param to prevent non-sysctl arguments from
triggering the current print.
Or delete the print and keep it silent for a little better performance.
Which is better?


>> + }
>
> Shouldn't you return an error here? Also my understanding is that
> parse_args is responsible for reporting the error.
>
All exception branches in process_sysctl_arg record logs and return 0.
Do I need to keep the same processing in the new branch?


>> +
>> if (strncmp(param, "sysctl", sizeof("sysctl") - 1) == 0) {
>> param += sizeof("sysctl") - 1;
>>
>> --
>> 2.27.0
>

Thanks
Xiaoming Ni

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