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.
