On 5/24/2024 12:33 PM, Greg KH wrote:
> On Fri, May 24, 2024 at 12:20:03PM +0800, Zijun Hu wrote:
>> zap_modalias_env() wrongly calculates size of memory block
>> to move, so maybe cause OOB memory access issue, fixed by
>> correcting size to memmove.
>
> "maybe" or "does"? That's a big difference :)
>
i found this issue by reading code instead of really meeting this issue.
this issue should be prone to happen if there are more than 1 other
environment vars.
do you have suggestion about term to use?
>>
>> Fixes: 9b3fa47d4a76 ("kobject: fix suppressing modalias in uevents delivered over netlink")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Zijun Hu <quic_zijuhu@xxxxxxxxxxx>
>> ---
>> lib/kobject_uevent.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
>> index 03b427e2707e..f153b4f9d4d9 100644
>> --- a/lib/kobject_uevent.c
>> +++ b/lib/kobject_uevent.c
>> @@ -434,7 +434,7 @@ static void zap_modalias_env(struct kobj_uevent_env *env)
>>
>> if (i != env->envp_idx - 1) {
>> memmove(env->envp[i], env->envp[i + 1],
>> - env->buflen - len);
>> + env->buf + env->buflen - env->envp[i + 1]);
>
> How is this "more correct"? Please explain it better, this logic is not
> obvious at all.
>
env->envp[] contains pointers to env->buf[] with length env->buflen,
we want to delete environment variable pointed by env->envp[i] with
length @len as shown below.
env->buf[] |-> target block <-|
0-----------------------------------------env->buflen
^ ^
| -> @len <- |
env->envp[i] env->envp[i+1]
so move "target block" forward by @len, so size of target block is
env->buf + env->buflen - env->envp[i+1] instead of env->buflen
-len.
do you suggest add inline comments to explain it ?
> thanks,
>
> greg k-h
