On 09/13/2018 01:11 PM, Michal Hocko wrote: > On Thu 13-09-18 09:12:04, peter enderborg wrote: >> On 09/13/2018 08:26 AM, Tetsuo Handa wrote: >>> On 2018/09/13 12:02, Paul Moore wrote: >>>> On Fri, Sep 7, 2018 at 12:43 PM Tetsuo Handa >>>> <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote: >>>>> syzbot is hitting warning at str_read() [1] because len parameter can >>>>> become larger than KMALLOC_MAX_SIZE. We don't need to emit warning for >>>>> this case. >>>>> >>>>> [1] https://syzkaller.appspot.com/bug?id=7f2f5aad79ea8663c296a2eedb81978401a908f0 >>>>> >>>>> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> >>>>> Reported-by: syzbot <syzbot+ac488b9811036cea7ea0@xxxxxxxxxxxxxxxxxxxxxxxxx> >>>>> --- >>>>> security/selinux/ss/policydb.c | 2 +- >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>> >>>>> diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c >>>>> index e9394e7..f4eadd3 100644 >>>>> --- a/security/selinux/ss/policydb.c >>>>> +++ b/security/selinux/ss/policydb.c >>>>> @@ -1101,7 +1101,7 @@ static int str_read(char **strp, gfp_t flags, void *fp, u32 len) >>>>> if ((len == 0) || (len == (u32)-1)) >>>>> return -EINVAL; >>>>> >>>>> - str = kmalloc(len + 1, flags); >>>>> + str = kmalloc(len + 1, flags | __GFP_NOWARN); >>>>> if (!str) >>>>> return -ENOMEM; >>>> Thanks for the patch. >>>> >>>> My eyes are starting to glaze over a bit chasing down all of the >>>> different kmalloc() code paths trying to ensure that this always does >>>> the right thing based on size of the allocation and the different slab >>>> allocators ... are we sure that this will always return NULL when (len >>>> + 1) is greater than KMALLOC_MAX_SIZE for the different slab allocator >>>> configurations? >>>> >>> Yes, for (len + 1) cannot become 0 (which causes kmalloc() to return >>> ZERO_SIZE_PTR) due to (len == (u32)-1) check above. >>> >>> The only concern would be whether you want allocation failure messages. >>> I assumed you don't need it because we are returning -ENOMEM to the caller. >>> >> Would it not be better with >> >> char *str; >> >> if ((len == 0) || (len == (u32)-1) || (len >= KMALLOC_MAX_SIZE)) >> return -EINVAL; >> >> str = kmalloc(len + 1, flags); >> if (!str) >> return -ENOMEM; > I strongly suspect that you want kvmalloc rather than kmalloc here. The > larger the request the more likely is the allocation to fail. > > I am not familiar with the code but I assume this is a root only > interface so we don't have to worry about nasty users scenario. > I don't think we get any big data there at all. Usually less than 32 bytes. However this data can be in fast path so a vmalloc is not an option. And some of the calls are GFP_ATOMC.
