From 1853c949646005b5959c483becde86608f548f24 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Thu, 10 Sep 2015 20:05:46 +0200 Subject: [PATCH] netlink, mmap: transform mmap skb into full skb on taps Ken-ichirou reported that running netlink in mmap mode for receive in combination with nlmon will throw a NULL pointer dereference in __kfree_skb() on nlmon_xmit(), in my case I can also trigger an "unable to handle kernel paging request". The problem is the skb_clone() in __netlink_deliver_tap_skb() for skbs that are mmaped. I.e. the cloned skb doesn't have a destructor, whereas the mmap netlink skb has it pointed to netlink_skb_destructor(), set in the handler netlink_ring_setup_skb(). There, skb->head is being set to NULL, so that in such cases, __kfree_skb() doesn't perform a skb_release_data() via skb_release_all(), where skb->head is possibly being freed through kfree(head) into slab allocator, although netlink mmap skb->head points to the mmap buffer. Similarly, the same has to be done also for large netlink skbs where the data area is vmalloced. Therefore, as discussed, make a copy for these rather rare cases for now. This fixes the issue on my and Ken-ichirou's test-cases. Reference: http://thread.gmane.org/gmane.linux.network/371129 Fixes: bcbde0d449ed ("net: netlink: virtual tap device management") Reported-by: Ken-ichirou MATSUZAWA Signed-off-by: Daniel Borkmann Tested-by: Ken-ichirou MATSUZAWA Signed-off-by: David S. Miller --- Reading git-format-patch failed