inet: frag: don't re-use chainlist for evictor (d1fe1944) · Commits · 戴 / test

commit ("inet: frags: fix a race between inet_evict_bucket and inet_frag_kill") describes the bug, but the fix doesn't work reliably. Problem is that ->flags member can be set on other cpu without chainlock being held by that task, i.e. the RMW-Cycle can clear INET_FRAG_EVICTED bit after we put the element on the evictor private list. We can crash when walking the 'private' evictor list since an element can be deleted from list underneath the evictor. Join work with Nikolay Alexandrov. Fixes: ("inet: frag: move eviction of queues to work queue") Reported-by:

Johan Schuijt <johan@transip.nl> Tested-by:

Frank Schreuder <fschreuder@transip.nl> Signed-off-by:

Nikolay Alexandrov <nikolay@cumulusnetworks.com> Signed-off-by:

Florian Westphal <fw@strlen.de> Signed-off-by:

David S. Miller <davem@davemloft.net>

include/net/inet_frag.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -45,6 +45,7 @@ enum {
		* @flags: fragment queue flags
		* @max_size: maximum received fragment size
		* @net: namespace that this frag belongs to
		* @list_evictor: list of queues to forcefully evict (e.g. due to low memory)
		*/
		struct inet_frag_queue {
		spinlock_t lock;
		@@ -59,6 +60,7 @@ struct inet_frag_queue {
		__u8 flags;
		u16 max_size;
		struct netns_frags *net;
		struct hlist_node list_evictor;
		};

		#define INETFRAGS_HASHSZ 1024

net/ipv4/inet_fragment.c

+3 −5

Original line number	Diff line number	Diff line
		@@ -151,14 +151,13 @@ evict_again:
		}

		fq->flags \|= INET_FRAG_EVICTED;
		hlist_del(&fq->list);
		hlist_add_head(&fq->list, &expired);
		hlist_add_head(&fq->list_evictor, &expired);
		++evicted;
		}

		spin_unlock(&hb->chain_lock);

		hlist_for_each_entry_safe(fq, n, &expired, list)
		hlist_for_each_entry_safe(fq, n, &expired, list_evictor)
		f->frag_expire((unsigned long) fq);

		return evicted;
		@@ -284,7 +283,6 @@ static inline void fq_unlink(struct inet_frag_queue fq, struct inet_frags f)
		struct inet_frag_bucket *hb;

		hb = get_frag_bucket_locked(fq, f);
		if (!(fq->flags & INET_FRAG_EVICTED))
		hlist_del(&fq->list);
		spin_unlock(&hb->chain_lock);
		}

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