[PATCH] smackfs: restrict bytes count in smackfs write functions

[Tetsuo Handa]

On 2021/01/26 3:08, Casey Schaufler wrote:
> On 1/24/2021 6:36 AM, Sabyrzhan Tasbolatov wrote:
>> syzbot found WARNINGs in several smackfs write operations where
>> bytes count is passed to memdup_user_nul which exceeds
>> GFP MAX_ORDER. Check count size if bigger SMK_LONGLABEL,
>> for smk_write_syslog if bigger than PAGE_SIZE - 1.
>>
>> Reported-by: syzbot+a71a442385a0b2815497 at syzkaller.appspotmail.com
>> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll at gmail.com>
> 
> Thank you for the patch. Unfortunately, SMK_LONGLABEL isn't
> the right value in some of these cases. 
> 

Since it uses sscanf(), I think that whitespaces must be excluded from upper limit
check. I'm proposing adding __GFP_NOWARM on the memdup_user_nul() side at
https://lkml.kernel.org/r/20210120103436.11830-1-penguin-kernel@I-love.SAKURA.ne.jp .