selinux: Add __GFP_NOWARN to allocation at str_read()

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 <[email protected]>
Reported-by: syzbot <[email protected]>
Signed-off-by: Paul Moore <[email protected]>

Author: Tetsuo Handa

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;