Initial discussion is that this bug is not easily addressable. Any fragmentation handler is subject to getting poisoned.
Begin forwarded message: Date: Wed, 31 Mar 2021 22:39:12 +0000 From: bugzilla-dae...@bugzilla.kernel.org To: step...@networkplumber.org Subject: [Bug 212515] New: DoS Attack on Fragment Cache https://bugzilla.kernel.org/show_bug.cgi?id=212515 Bug ID: 212515 Summary: DoS Attack on Fragment Cache Product: Networking Version: 2.5 Kernel Version: 5.12.0-rc5 Hardware: All OS: Linux Tree: Mainline Status: NEW Severity: normal Priority: P1 Component: IPV4 Assignee: step...@networkplumber.org Reporter: kman...@ucr.edu Regression: No Hi, After the kernel receives an IPv4 fragment, it will try to fit it into a queue by calling function struct inet_frag_queue *inet_frag_find(struct fqdir *fqdir, void *key) in net/ipv4/inet_fragment.c. However, this function will first check if the existing fragment memory exceeds the fqdir->high_thresh. If it exceeds, then drop the fragment regradless it belongs to a new queue or an existing queue. Chances are that an attacker can fill the cache with fragments that will never be assembled (i.e., only sends the first fragment with new IPIDs every time) to exceed the threshold so that all future incoming fragmented IPv4 traffic would be blocked and dropped. Since there is GC machanism, the victim host has to wait for 30s when the fragments are expired to continue receive incoming fragments normally. In pratice, given the 4MB fragment cache, the attacker only needs to send 1766 fragments to exhaust the cache and DoS the victim for 30s, whose cost is pretty low. Besides, IPv6 would also be affected since the issue resides in inet part. This issue is introduced in commit 648700f76b03b7e8149d13cc2bdb3355035258a9 (inet: frags: use rhashtables for reassembly units) which removes fqdir->low_thresh, which is used by GC worker. I would recommand to bring GC worker back to prevent the DoS attacks. Thanks, Keyu Man -- You may reply to this email to add a comment. You are receiving this mail because: You are the assignee for the bug.
