[PATCH v2 net-next 0/3] net: device tracking improvements

[PATCH v2 net-next 0/3] net: device tracking improvements

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

Main goal of this series is to be able to detect the following case
which apparently is still haunting us.

dev_hold_track(dev, tracker_1, GFP_ATOMIC);
    dev_hold(dev);
    dev_put(dev);
    dev_put(dev);              // Should complain loudly here.
dev_put_track(dev, tracker_1); // instead of here (as before this series)


v2: third patch:
  I replaced the dev_put() in linkwatch_do_dev() with __dev_put().

Eric Dumazet (3):
  ref_tracker: implement use-after-free detection
  ref_tracker: add a count of untracked references
  net: refine dev_put()/dev_hold() debugging

 include/linux/netdevice.h   | 69 ++++++++++++++++++++++++-------------
 include/linux/ref_tracker.h |  4 +++
 lib/ref_tracker.c           | 17 ++++++++-
 net/core/dev.c              |  2 +-
 net/core/link_watch.c       |  6 ++--
 5 files changed, 70 insertions(+), 28 deletions(-)

-- 
2.35.0.263.gb82422642f-goog

[PATCH v2 net-next 1/3] ref_tracker: implement use-after-free detection

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

Whenever ref_tracker_dir_init() is called, mark the struct ref_tracker_dir
as dead.

Test the dead status from ref_tracker_alloc() and ref_tracker_free()

This should detect buggy dev_put()/dev_hold() happening too late
in netdevice dismantle process.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/linux/ref_tracker.h | 2 ++
 lib/ref_tracker.c           | 5 +++++
 2 files changed, 7 insertions(+)

diff --git a/include/linux/ref_tracker.h b/include/linux/ref_tracker.h
index 60f3453be23e6881725d383c55f93143fda1e7a2..a443abda937d86ff534225bf16b958a9da295a7d 100644
--- a/include/linux/ref_tracker.h
+++ b/include/linux/ref_tracker.h
@@ -13,6 +13,7 @@ struct ref_tracker_dir {
 	spinlock_t		lock;
 	unsigned int		quarantine_avail;
 	refcount_t		untracked;
+	bool			dead;
 	struct list_head	list; /* List of active trackers */
 	struct list_head	quarantine; /* List of dead trackers */
 #endif
@@ -26,6 +27,7 @@ static inline void ref_tracker_dir_init(struct ref_tracker_dir *dir,
 	INIT_LIST_HEAD(&dir->quarantine);
 	spin_lock_init(&dir->lock);
 	dir->quarantine_avail = quarantine_count;
+	dir->dead = false;
 	refcount_set(&dir->untracked, 1);
 	stack_depot_init();
 }
diff --git a/lib/ref_tracker.c b/lib/ref_tracker.c
index a6789c0c626b0f68ad67c264cd19177a63fb82d2..32ff6bd497f8e464eeb51a3628cb24bded0547da 100644
--- a/lib/ref_tracker.c
+++ b/lib/ref_tracker.c
@@ -20,6 +20,7 @@ void ref_tracker_dir_exit(struct ref_tracker_dir *dir)
 	unsigned long flags;
 	bool leak = false;
 
+	dir->dead = true;
 	spin_lock_irqsave(&dir->lock, flags);
 	list_for_each_entry_safe(tracker, n, &dir->quarantine, head) {
 		list_del(&tracker->head);
@@ -72,6 +73,8 @@ int ref_tracker_alloc(struct ref_tracker_dir *dir,
 	gfp_t gfp_mask = gfp;
 	unsigned long flags;
 
+	WARN_ON_ONCE(dir->dead);
+
 	if (gfp & __GFP_DIRECT_RECLAIM)
 		gfp_mask |= __GFP_NOFAIL;
 	*trackerp = tracker = kzalloc(sizeof(*tracker), gfp_mask);
@@ -100,6 +103,8 @@ int ref_tracker_free(struct ref_tracker_dir *dir,
 	unsigned int nr_entries;
 	unsigned long flags;
 
+	WARN_ON_ONCE(dir->dead);
+
 	if (!tracker) {
 		refcount_dec(&dir->untracked);
 		return -EEXIST;
-- 
2.35.0.263.gb82422642f-goog

[PATCH v2 net-next 2/3] ref_tracker: add a count of untracked references

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

We are still chasing a netdev refcount imbalance, and we suspect
we have one rogue dev_put() that is consuming a reference taken
from a dev_hold_track()

To detect this case, allow ref_tracker_alloc() and ref_tracker_free()
to be called with a NULL @trackerp parameter, and use a dedicated
refcount_t just for them.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/linux/ref_tracker.h |  2 ++
 lib/ref_tracker.c           | 12 +++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/linux/ref_tracker.h b/include/linux/ref_tracker.h
index a443abda937d86ff534225bf16b958a9da295a7d..9ca353ab712b5e897d9b3e5cfcd7117b610dd01a 100644
--- a/include/linux/ref_tracker.h
+++ b/include/linux/ref_tracker.h
@@ -13,6 +13,7 @@ struct ref_tracker_dir {
 	spinlock_t		lock;
 	unsigned int		quarantine_avail;
 	refcount_t		untracked;
+	refcount_t		no_tracker;
 	bool			dead;
 	struct list_head	list; /* List of active trackers */
 	struct list_head	quarantine; /* List of dead trackers */
@@ -29,6 +30,7 @@ static inline void ref_tracker_dir_init(struct ref_tracker_dir *dir,
 	dir->quarantine_avail = quarantine_count;
 	dir->dead = false;
 	refcount_set(&dir->untracked, 1);
+	refcount_set(&dir->no_tracker, 1);
 	stack_depot_init();
 }
 
diff --git a/lib/ref_tracker.c b/lib/ref_tracker.c
index 32ff6bd497f8e464eeb51a3628cb24bded0547da..9c0c2e09df666d19aba441f568762afbd1cad4d0 100644
--- a/lib/ref_tracker.c
+++ b/lib/ref_tracker.c
@@ -38,6 +38,7 @@ void ref_tracker_dir_exit(struct ref_tracker_dir *dir)
 	spin_unlock_irqrestore(&dir->lock, flags);
 	WARN_ON_ONCE(leak);
 	WARN_ON_ONCE(refcount_read(&dir->untracked) != 1);
+	WARN_ON_ONCE(refcount_read(&dir->no_tracker) != 1);
 }
 EXPORT_SYMBOL(ref_tracker_dir_exit);
 
@@ -75,6 +76,10 @@ int ref_tracker_alloc(struct ref_tracker_dir *dir,
 
 	WARN_ON_ONCE(dir->dead);
 
+	if (!trackerp) {
+		refcount_inc(&dir->no_tracker);
+		return 0;
+	}
 	if (gfp & __GFP_DIRECT_RECLAIM)
 		gfp_mask |= __GFP_NOFAIL;
 	*trackerp = tracker = kzalloc(sizeof(*tracker), gfp_mask);
@@ -98,13 +103,18 @@ int ref_tracker_free(struct ref_tracker_dir *dir,
 		     struct ref_tracker **trackerp)
 {
 	unsigned long entries[REF_TRACKER_STACK_ENTRIES];
-	struct ref_tracker *tracker = *trackerp;
 	depot_stack_handle_t stack_handle;
+	struct ref_tracker *tracker;
 	unsigned int nr_entries;
 	unsigned long flags;
 
 	WARN_ON_ONCE(dir->dead);
 
+	if (!trackerp) {
+		refcount_dec(&dir->no_tracker);
+		return 0;
+	}
+	tracker = *trackerp;
 	if (!tracker) {
 		refcount_dec(&dir->untracked);
 		return -EEXIST;
-- 
2.35.0.263.gb82422642f-goog

[PATCH v2 net-next 3/3] net: refine dev_put()/dev_hold() debugging

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

We are still chasing some syzbot reports where we think a rogue dev_put()
is called with no corresponding prior dev_hold().
Unfortunately it eats a reference on dev->dev_refcnt taken by innocent
dev_hold_track(), meaning that the refcount saturation splat comes
too late to be useful.

Make sure that 'not tracked' dev_put() and dev_hold() better use
CONFIG_NET_DEV_REFCNT_TRACKER=y debug infrastructure:

Prior patch in the series allowed ref_tracker_alloc() and ref_tracker_free()
to be called with a NULL @trackerp parameter, and to use a separate refcount
only to detect too many put() even in the following case:

dev_hold_track(dev, tracker_1, GFP_ATOMIC);
 dev_hold(dev);
 dev_put(dev);
 dev_put(dev); // Should complain loudly here.
dev_put_track(dev, tracker_1); // instead of here

Add clarification about netdev_tracker_alloc() role.

v2: I replaced the dev_put() in linkwatch_do_dev()
    with __dev_put() because callers called netdev_tracker_free().

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/linux/netdevice.h | 69 ++++++++++++++++++++++++++-------------
 net/core/dev.c            |  2 +-
 net/core/link_watch.c     |  6 ++--
 3 files changed, 50 insertions(+), 27 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index e490b84732d1654bf067b30f2bb0b0825f88dea9..3fb6fb67ed77e70314a699c9bdf8f4b26acfcc19 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3817,14 +3817,7 @@ extern unsigned int	netdev_budget_usecs;
 /* Called by rtnetlink.c:rtnl_unlock() */
 void netdev_run_todo(void);
 
-/**
- *	dev_put - release reference to device
- *	@dev: network device
- *
- * Release reference to device to allow it to be freed.
- * Try using dev_put_track() instead.
- */
-static inline void dev_put(struct net_device *dev)
+static inline void __dev_put(struct net_device *dev)
 {
 	if (dev) {
 #ifdef CONFIG_PCPU_DEV_REFCNT
@@ -3835,14 +3828,7 @@ static inline void dev_put(struct net_device *dev)
 	}
 }
 
-/**
- *	dev_hold - get reference to device
- *	@dev: network device
- *
- * Hold reference to device to keep it from being freed.
- * Try using dev_hold_track() instead.
- */
-static inline void dev_hold(struct net_device *dev)
+static inline void __dev_hold(struct net_device *dev)
 {
 	if (dev) {
 #ifdef CONFIG_PCPU_DEV_REFCNT
@@ -3853,11 +3839,24 @@ static inline void dev_hold(struct net_device *dev)
 	}
 }
 
+static inline void __netdev_tracker_alloc(struct net_device *dev,
+					  netdevice_tracker *tracker,
+					  gfp_t gfp)
+{
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+	ref_tracker_alloc(&dev->refcnt_tracker, tracker, gfp);
+#endif
+}
+
+/* netdev_tracker_alloc() can upgrade a prior untracked reference
+ * taken by dev_get_by_name()/dev_get_by_index() to a tracked one.
+ */
 static inline void netdev_tracker_alloc(struct net_device *dev,
 					netdevice_tracker *tracker, gfp_t gfp)
 {
 #ifdef CONFIG_NET_DEV_REFCNT_TRACKER
-	ref_tracker_alloc(&dev->refcnt_tracker, tracker, gfp);
+	refcount_dec(&dev->refcnt_tracker.no_tracker);
+	__netdev_tracker_alloc(dev, tracker, gfp);
 #endif
 }
 
@@ -3873,8 +3872,8 @@ static inline void dev_hold_track(struct net_device *dev,
 				  netdevice_tracker *tracker, gfp_t gfp)
 {
 	if (dev) {
-		dev_hold(dev);
-		netdev_tracker_alloc(dev, tracker, gfp);
+		__dev_hold(dev);
+		__netdev_tracker_alloc(dev, tracker, gfp);
 	}
 }
 
@@ -3883,10 +3882,34 @@ static inline void dev_put_track(struct net_device *dev,
 {
 	if (dev) {
 		netdev_tracker_free(dev, tracker);
-		dev_put(dev);
+		__dev_put(dev);
 	}
 }
 
+/**
+ *	dev_hold - get reference to device
+ *	@dev: network device
+ *
+ * Hold reference to device to keep it from being freed.
+ * Try using dev_hold_track() instead.
+ */
+static inline void dev_hold(struct net_device *dev)
+{
+	dev_hold_track(dev, NULL, GFP_ATOMIC);
+}
+
+/**
+ *	dev_put - release reference to device
+ *	@dev: network device
+ *
+ * Release reference to device to allow it to be freed.
+ * Try using dev_put_track() instead.
+ */
+static inline void dev_put(struct net_device *dev)
+{
+	dev_put_track(dev, NULL);
+}
+
 static inline void dev_replace_track(struct net_device *odev,
 				     struct net_device *ndev,
 				     netdevice_tracker *tracker,
@@ -3895,11 +3918,11 @@ static inline void dev_replace_track(struct net_device *odev,
 	if (odev)
 		netdev_tracker_free(odev, tracker);
 
-	dev_hold(ndev);
-	dev_put(odev);
+	__dev_hold(ndev);
+	__dev_put(odev);
 
 	if (ndev)
-		netdev_tracker_alloc(ndev, tracker, gfp);
+		__netdev_tracker_alloc(ndev, tracker, gfp);
 }
 
 /* Carrier loss detection, dial on demand. The functions netif_carrier_on
diff --git a/net/core/dev.c b/net/core/dev.c
index f79744d99413434ad28b26dee9aeeb2893a0e3ae..1eaa0b88e3ba5d800484656f2c3420af57050294 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10172,7 +10172,7 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 	dev->pcpu_refcnt = alloc_percpu(int);
 	if (!dev->pcpu_refcnt)
 		goto free_dev;
-	dev_hold(dev);
+	__dev_hold(dev);
 #else
 	refcount_set(&dev->dev_refcnt, 1);
 #endif
diff --git a/net/core/link_watch.c b/net/core/link_watch.c
index b0f5344d1185be66d05cd1dc50cffc5ccfe883ef..95098d1a49bdf4cbc3ddeb4d345e4276f974a208 100644
--- a/net/core/link_watch.c
+++ b/net/core/link_watch.c
@@ -166,10 +166,10 @@ static void linkwatch_do_dev(struct net_device *dev)
 
 		netdev_state_change(dev);
 	}
-	/* Note: our callers are responsible for
-	 * calling netdev_tracker_free().
+	/* Note: our callers are responsible for calling netdev_tracker_free().
+	 * This is the reason we use __dev_put() instead of dev_put().
 	 */
-	dev_put(dev);
+	__dev_put(dev);
 }
 
 static void __linkwatch_run_queue(int urgent_only)
-- 
2.35.0.263.gb82422642f-goog

Re: [PATCH v2 net-next 0/3] net: device tracking improvements

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (master)
by David S. Miller <davem@davemloft.net>:

On Fri,  4 Feb 2022 14:42:34 -0800 you wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> Main goal of this series is to be able to detect the following case
> which apparently is still haunting us.
> 
> dev_hold_track(dev, tracker_1, GFP_ATOMIC);
>     dev_hold(dev);
>     dev_put(dev);
>     dev_put(dev);              // Should complain loudly here.
> dev_put_track(dev, tracker_1); // instead of here (as before this series)
> 
> [...]

Here is the summary with links:
  - [v2,net-next,1/3] ref_tracker: implement use-after-free detection
    https://git.kernel.org/netdev/net-next/c/e3ececfe668f
  - [v2,net-next,2/3] ref_tracker: add a count of untracked references
    https://git.kernel.org/netdev/net-next/c/8fd5522f44dc
  - [v2,net-next,3/3] net: refine dev_put()/dev_hold() debugging
    https://git.kernel.org/netdev/net-next/c/4c6c11ea0f7b

You are awesome, thank you!
-- 
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