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| author | Alexei Starovoitov <ast@fb.com> | 2017-03-07 20:00:12 -0800 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2017-03-09 13:27:17 -0800 |
| commit | 9f691549f76d488a0c74397b3e51e943865ea01f (patch) | |
| tree | c73054636fa049cf4eee1b15a0eac5191b926e6f /kernel | |
| parent | 745cb7f8a5de0805cade3de3991b7a95317c7c73 (diff) | |
| download | linux-0-day-9f691549f76d488a0c74397b3e51e943865ea01f.tar.gz linux-0-day-9f691549f76d488a0c74397b3e51e943865ea01f.tar.xz | |
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>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/bpf/hashtab.c | 25 |
1 files changed, 20 insertions, 5 deletions
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index 3ea87fb19a941..63c86a7be2a1d 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); |