| Message ID | 20250110130703.3814407-3-linyunsheng@huawei.com (mailing list archive) |
|---|---|
| State | New |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | fix two bugs related to page_pool | expand |
Yunsheng Lin <linyunsheng@huawei.com> writes: > page_pool page may be freed from skb_defer_free_flush() in > softirq context without binding to any specific napi, it > may cause use-after-free problem due to the below time window, > as below, CPU1 may still access napi->list_owner after CPU0 > free the napi memory: > > CPU 0 CPU1 > page_pool_destroy() skb_defer_free_flush() > . . > . napi = READ_ONCE(pool->p.napi); > . . > page_pool_disable_direct_recycling() . > driver free napi memory . > . . > . napi && READ_ONCE(napi->list_owner) == cpuid > . . Have you actually observed this happen, or are you just speculating? Because I don't think it can; deleting a NAPI instance already requires observing an RCU grace period, cf netdevice.h: /** * __netif_napi_del - remove a NAPI context * @napi: NAPI context * * Warning: caller must observe RCU grace period before freeing memory * containing @napi. Drivers might want to call this helper to combine * all the needed RCU grace periods into a single one. */ void __netif_napi_del(struct napi_struct *napi); /** * netif_napi_del - remove a NAPI context * @napi: NAPI context * * netif_napi_del() removes a NAPI context from the network device NAPI list */ static inline void netif_napi_del(struct napi_struct *napi) { __netif_napi_del(napi); synchronize_net(); } > Use rcu mechanism to avoid the above problem. > > Note, the above was found during code reviewing on how to fix > the problem in [1]. > > As the following IOMMU fix patch depends on synchronize_rcu() > added in this patch and the time window is so small that it > doesn't seem to be an urgent fix, so target the net-next as > the IOMMU fix patch does. > > 1. https://lore.kernel.org/lkml/8067f204-1380-4d37-8ffd-007fc6f26738@kernel.org/T/ > > Fixes: dd64b232deb8 ("page_pool: unlink from napi during destroy") > Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com> > CC: Alexander Lobakin <aleksander.lobakin@intel.com> > Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com> > --- > net/core/page_pool.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/net/core/page_pool.c b/net/core/page_pool.c > index 9733206d6406..1aa7b93bdcc8 100644 > --- a/net/core/page_pool.c > +++ b/net/core/page_pool.c > @@ -799,6 +799,7 @@ __page_pool_put_page(struct page_pool *pool, netmem_ref netmem, > static bool page_pool_napi_local(const struct page_pool *pool) > { > const struct napi_struct *napi; > + bool napi_local; > u32 cpuid; > > if (unlikely(!in_softirq())) > @@ -814,9 +815,15 @@ static bool page_pool_napi_local(const struct page_pool *pool) > if (READ_ONCE(pool->cpuid) == cpuid) > return true; > > + /* Synchronizated with page_pool_destory() to avoid use-after-free > + * for 'napi'. > + */ > + rcu_read_lock(); > napi = READ_ONCE(pool->p.napi); > + napi_local = napi && READ_ONCE(napi->list_owner) == cpuid; > + rcu_read_unlock(); This rcu_read_lock/unlock() pair is redundant in the context you mention above, since skb_defer_free_flush() is only ever called from softirq context (within local_bh_disable()), which already function as an RCU read lock. > - return napi && READ_ONCE(napi->list_owner) == cpuid; > + return napi_local; > } > > void page_pool_put_unrefed_netmem(struct page_pool *pool, netmem_ref netmem, > @@ -1165,6 +1172,12 @@ void page_pool_destroy(struct page_pool *pool) > if (!page_pool_release(pool)) > return; > > + /* Paired with rcu lock in page_pool_napi_local() to enable clearing > + * of pool->p.napi in page_pool_disable_direct_recycling() is seen > + * before returning to driver to free the napi instance. > + */ > + synchronize_rcu(); Most drivers call page_pool_destroy() in a loop for each RX queue, so now you're introducing a full synchronize_rcu() wait for each queue. That can delay tearing down the device significantly, so I don't think this is a good idea. -Toke
diff --git a/net/core/page_pool.c b/net/core/page_pool.c index 9733206d6406..1aa7b93bdcc8 100644 --- a/net/core/page_pool.c +++ b/net/core/page_pool.c @@ -799,6 +799,7 @@ __page_pool_put_page(struct page_pool *pool, netmem_ref netmem, static bool page_pool_napi_local(const struct page_pool *pool) { const struct napi_struct *napi; + bool napi_local; u32 cpuid; if (unlikely(!in_softirq())) @@ -814,9 +815,15 @@ static bool page_pool_napi_local(const struct page_pool *pool) if (READ_ONCE(pool->cpuid) == cpuid) return true; + /* Synchronizated with page_pool_destory() to avoid use-after-free + * for 'napi'. + */ + rcu_read_lock(); napi = READ_ONCE(pool->p.napi); + napi_local = napi && READ_ONCE(napi->list_owner) == cpuid; + rcu_read_unlock(); - return napi && READ_ONCE(napi->list_owner) == cpuid; + return napi_local; } void page_pool_put_unrefed_netmem(struct page_pool *pool, netmem_ref netmem, @@ -1165,6 +1172,12 @@ void page_pool_destroy(struct page_pool *pool) if (!page_pool_release(pool)) return; + /* Paired with rcu lock in page_pool_napi_local() to enable clearing + * of pool->p.napi in page_pool_disable_direct_recycling() is seen + * before returning to driver to free the napi instance. + */ + synchronize_rcu(); + page_pool_detached(pool); pool->defer_start = jiffies; pool->defer_warn = jiffies + DEFER_WARN_INTERVAL;
page_pool page may be freed from skb_defer_free_flush() in softirq context without binding to any specific napi, it may cause use-after-free problem due to the below time window, as below, CPU1 may still access napi->list_owner after CPU0 free the napi memory: CPU 0 CPU1 page_pool_destroy() skb_defer_free_flush() . . . napi = READ_ONCE(pool->p.napi); . . page_pool_disable_direct_recycling() . driver free napi memory . . . . napi && READ_ONCE(napi->list_owner) == cpuid . . Use rcu mechanism to avoid the above problem. Note, the above was found during code reviewing on how to fix the problem in [1]. As the following IOMMU fix patch depends on synchronize_rcu() added in this patch and the time window is so small that it doesn't seem to be an urgent fix, so target the net-next as the IOMMU fix patch does. 1. https://lore.kernel.org/lkml/8067f204-1380-4d37-8ffd-007fc6f26738@kernel.org/T/ Fixes: dd64b232deb8 ("page_pool: unlink from napi during destroy") Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com> CC: Alexander Lobakin <aleksander.lobakin@intel.com> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com> --- net/core/page_pool.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)