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Subject[PATCH 4.8 15/49] bpf: fix htab map destruction when extra reserve is in use
4.8-stable review patch.  If anyone has any objections, please let me know.


From: Daniel Borkmann <>

[ 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.

Fixes: a6ed3ea65d98 ("bpf: restore behavior of bpf_map_update_elem")
Reported-by: Dmitry Vyukov <>
Signed-off-by: Daniel Borkmann <>
Acked-by: Alexei Starovoitov <>
Signed-off-by: David S. Miller <>
Signed-off-by: Greg Kroah-Hartman <>
kernel/bpf/hashtab.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -687,7 +687,8 @@ static void delete_all_elements(struct b

hlist_for_each_entry_safe(l, n, head, hash_node) {
- htab_elem_free(htab, l);
+ if (l->state != HTAB_EXTRA_ELEM_USED)
+ htab_elem_free(htab, l);

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