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authorAlexei Starovoitov <ast@fb.com>2017-03-07 20:00:12 -0800
committerDavid S. Miller <davem@davemloft.net>2017-03-09 13:27:17 -0800
commit9f691549f76d488a0c74397b3e51e943865ea01f (patch)
treec73054636fa049cf4eee1b15a0eac5191b926e6f
parent745cb7f8a5de0805cade3de3991b7a95317c7c73 (diff)
bpf: fix struct htab_elem layout
when htab_elem is removed from the bucket list the htab_elem.hash_node.next field should not be overridden too early otherwise we have a tiny race window between lookup and delete. The bug was discovered by manual code analysis and reproducible only with explicit udelay() in lookup_elem_raw(). Fixes: 6c9059817432 ("bpf: pre-allocate hash map elements") Reported-by: Jonathan Perry <jonperry@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--kernel/bpf/hashtab.c25
1 files changed, 20 insertions, 5 deletions
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 3ea87fb19a94..63c86a7be2a1 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -45,8 +45,13 @@ enum extra_elem_state {
struct htab_elem {
union {
struct hlist_node hash_node;
- struct bpf_htab *htab;
- struct pcpu_freelist_node fnode;
+ struct {
+ void *padding;
+ union {
+ struct bpf_htab *htab;
+ struct pcpu_freelist_node fnode;
+ };
+ };
};
union {
struct rcu_head rcu;
@@ -162,7 +167,8 @@ skip_percpu_elems:
offsetof(struct htab_elem, lru_node),
htab->elem_size, htab->map.max_entries);
else
- pcpu_freelist_populate(&htab->freelist, htab->elems,
+ pcpu_freelist_populate(&htab->freelist,
+ htab->elems + offsetof(struct htab_elem, fnode),
htab->elem_size, htab->map.max_entries);
return 0;
@@ -217,6 +223,11 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
int err, i;
u64 cost;
+ BUILD_BUG_ON(offsetof(struct htab_elem, htab) !=
+ offsetof(struct htab_elem, hash_node.pprev));
+ BUILD_BUG_ON(offsetof(struct htab_elem, fnode.next) !=
+ offsetof(struct htab_elem, hash_node.pprev));
+
if (lru && !capable(CAP_SYS_ADMIN))
/* LRU implementation is much complicated than other
* maps. Hence, limit to CAP_SYS_ADMIN for now.
@@ -582,9 +593,13 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
int err = 0;
if (prealloc) {
- l_new = (struct htab_elem *)pcpu_freelist_pop(&htab->freelist);
- if (!l_new)
+ struct pcpu_freelist_node *l;
+
+ l = pcpu_freelist_pop(&htab->freelist);
+ if (!l)
err = -E2BIG;
+ else
+ l_new = container_of(l, struct htab_elem, fnode);
} else {
if (atomic_inc_return(&htab->count) > htab->map.max_entries) {
atomic_dec(&htab->count);