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bpf: Avoid kfree_rcu() under lock in bpf_lpm_trie.

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syzbot reported the following lock sequence:
cpu 2:
  grabs timer_base lock
    spins on bpf_lpm lock

cpu 1:
  grab rcu krcp lock
    spins on timer_base lock

cpu 0:
  grab bpf_lpm lock
    spins on rcu krcp lock

bpf_lpm lock can be the same.
timer_base lock can also be the same due to timer migration.
but rcu krcp lock is always per-cpu, so it cannot be the same lock.
Hence it's a false positive.
To avoid lockdep complaining move kfree_rcu() after spin_unlock.

Reported-by: syzbot+1fa663a2100308ab6eab@syzkaller.appspotmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240329171439.37813-1-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2024-03-29 10:14:39 -07:00 committed by Andrii Nakryiko
parent 201874fc06
commit 59f2f84117
1 changed files with 9 additions and 4 deletions
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13
kernel/bpf/lpm_trie.c
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@ -316,6 +316,7 @@ static long trie_update_elem(struct bpf_map *map,
{
struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
struct lpm_trie_node *node, *im_node = NULL, *new_node = NULL;
struct lpm_trie_node *free_node = NULL;
struct lpm_trie_node __rcu **slot;
struct bpf_lpm_trie_key_u8 *key = _key;
unsigned long irq_flags;
@ -390,7 +391,7 @@ static long trie_update_elem(struct bpf_map *map,
trie->n_entries--;
rcu_assign_pointer(*slot, new_node);
kfree_rcu(node, rcu);
free_node = node;
goto out;
}
@ -437,6 +438,7 @@ static long trie_update_elem(struct bpf_map *map,
}
spin_unlock_irqrestore(&trie->lock, irq_flags);
kfree_rcu(free_node, rcu);
return ret;
}
@ -445,6 +447,7 @@ static long trie_update_elem(struct bpf_map *map,
static long trie_delete_elem(struct bpf_map *map, void *_key)
{
struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
struct lpm_trie_node *free_node = NULL, *free_parent = NULL;
struct bpf_lpm_trie_key_u8 *key = _key;
struct lpm_trie_node __rcu **trim, **trim2;
struct lpm_trie_node *node, *parent;
@ -514,8 +517,8 @@ static long trie_delete_elem(struct bpf_map *map, void *_key)
else
rcu_assign_pointer(
*trim2, rcu_access_pointer(parent->child[0]));
kfree_rcu(parent, rcu);
kfree_rcu(node, rcu);
free_parent = parent;
free_node = node;
goto out;
}
@ -529,10 +532,12 @@ static long trie_delete_elem(struct bpf_map *map, void *_key)
rcu_assign_pointer(*trim, rcu_access_pointer(node->child[1]));
else
RCU_INIT_POINTER(*trim, NULL);
kfree_rcu(node, rcu);
free_node = node;
out:
spin_unlock_irqrestore(&trie->lock, irq_flags);
kfree_rcu(free_parent, rcu);
kfree_rcu(free_node, rcu);
return ret;
}