Patch "bpf: fix htab map destruction when extra reserve is in use" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

bpf: fix htab map destruction when extra reserve is in use

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
bpf-fix-htab-map-destruction-when-extra-reserve-is-in-use.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Daniel Borkmann <[email protected]>
Date: Fri, 4 Nov 2016 00:01:19 +0100
Subject: bpf: fix htab map destruction when extra reserve is in use

From: Daniel Borkmann <[email protected]>

[ Upstream commit 483bed2b0ddd12ec33fc9407e0c6e1088e77a97c ]

Commit a6ed3ea65d98 ("bpf: restore behavior of bpf_map_update_elem") added an extra per-cpu reserve to the hash table map to restore old behaviour from pre prealloc times. When non-prealloc is in use for a map, then problem is that once a hash table extra element has been linked into the hash-table, and the hash table is destroyed due to refcount dropping to zero, then htab_map_free() -> delete_all_elements() will walk the whole hash table and drop all elements via htab_elem_free(). The problem is that the element from the extra reserve is first fed to the wrong backend allocator and eventually freed twice.

---
 kernel/bpf/hashtab.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -687,7 +687,8 @@ static void delete_all_elements(struct b
 
 		hlist_for_each_entry_safe(l, n, head, hash_node) {
 			hlist_del_rcu(&l->hash_node);
-			htab_elem_free(htab, l);
+			if (l->state != HTAB_EXTRA_ELEM_USED)
+				htab_elem_free(htab, l);
 		}
 	}
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/dctcp-avoid-bogus-doubling-of-cwnd-after-loss.patch queue-4.8/bpf-fix-htab-map-destruction-when-extra-reserve-is-in-use.patch