6.5-stable review patch. If anyone has any objections, please let me know.
------------------
From: Song Liu <song@xxxxxxxxxx>
[ Upstream commit d35381aa73f7e1e8b25f3ed5283287a64d9ddff5 ]
htab_lock_bucket uses the following logic to avoid recursion:
1. preempt_disable();
2. check percpu counter htab->map_locked[hash] for recursion;
2.1. if map_lock[hash] is already taken, return -BUSY;
3. raw_spin_lock_irqsave();
However, if an IRQ hits between 2 and 3, BPF programs attached to the IRQ
logic will not able to access the same hash of the hashtab and get -EBUSY.
This -EBUSY is not really necessary. Fix it by disabling IRQ before
checking map_locked:
1. preempt_disable();
2. local_irq_save();
3. check percpu counter htab->map_locked[hash] for recursion;
3.1. if map_lock[hash] is already taken, return -BUSY;
4. raw_spin_lock().
Similarly, use raw_spin_unlock() and local_irq_restore() in
htab_unlock_bucket().
Fixes: 20b6cc34ea74 ("bpf: Avoid hashtab deadlock with map_locked")
Suggested-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Song Liu <song@xxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/bpf/7a9576222aa40b1c84ad3a9ba3e64011d1a04d41.camel@xxxxxxxxxxxxx
Link: https://lore.kernel.org/bpf/20231012055741.3375999-1-song@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
kernel/bpf/hashtab.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 56d3da7d0bc66..e209e748a8e05 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -155,13 +155,15 @@ static inline int htab_lock_bucket(const struct bpf_htab *htab,
hash = hash & min_t(u32, HASHTAB_MAP_LOCK_MASK, htab->n_buckets - 1);
preempt_disable();
+ local_irq_save(flags);
if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) {
__this_cpu_dec(*(htab->map_locked[hash]));
+ local_irq_restore(flags);
preempt_enable();
return -EBUSY;
}
- raw_spin_lock_irqsave(&b->raw_lock, flags);
+ raw_spin_lock(&b->raw_lock);
*pflags = flags;
return 0;
@@ -172,8 +174,9 @@ static inline void htab_unlock_bucket(const struct bpf_htab *htab,
unsigned long flags)
{
hash = hash & min_t(u32, HASHTAB_MAP_LOCK_MASK, htab->n_buckets - 1);
- raw_spin_unlock_irqrestore(&b->raw_lock, flags);
+ raw_spin_unlock(&b->raw_lock);
__this_cpu_dec(*(htab->map_locked[hash]));
+ local_irq_restore(flags);
preempt_enable();
}
--
2.42.0
