[PATCH v2 net 0/2] drop_monitor: take care of 32bit kernels

[PATCH v2 net 0/2] drop_monitor: take care of 32bit kernels

[Eric Dumazet]

This series fixes two drop_monitor issues on 32-bit architectures:

- Patch 1 uses nla_total_size_64bit() for PC and TIMESTAMP attributes to
  account for alignment padding added by nla_put_u64_64bit(), avoiding
  potential skb_over_panic() crashes.

- Patch 2 moves u64_stats updates before spin_unlock_irqrestore(), ensuring
  local interrupts are disabled to prevent seqcount corruption from nested
  interrupts in probe context.

Eric Dumazet (2):
  drop_monitor: fix size calculations for 64-bit attributes
  drop_monitor: perform u64_stats updates under IRQ-disabled section

 net/core/drop_monitor.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

-- 
2.55.0.229.g6434b31f56-goog

[PATCH v2 net 1/2] drop_monitor: fix size calculations for 64-bit attributes

[Eric Dumazet]

net_dm_packet_report_fill() and net_dm_hw_packet_report_fill() use
nla_put_u64_64bit() to append 64-bit attributes (NET_DM_ATTR_PC and
NET_DM_ATTR_TIMESTAMP).

On 32-bit architectures without CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS,
nla_put_u64_64bit() may append a 4-byte NET_DM_ATTR_PAD attribute for
64-bit alignment.

However, net_dm_packet_report_size() and net_dm_hw_packet_report_size()
used nla_total_size(sizeof(u64)) instead of nla_total_size_64bit(sizeof(u64)),
budgeting 12 bytes instead of up to 16 bytes.

This under-estimation of SKB size can lead to an skb_over_panic() when
__nla_reserve() or skb_put() is subsequently called.

Fix this by using nla_total_size_64bit(sizeof(u64)) in both size calculations.

Fixes: ca30707dee2b ("drop_monitor: Add packet alert mode")
Fixes: 5e58109b1ea4 ("drop_monitor: Add support for packet alert mode for hardware drops")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/core/drop_monitor.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 2bf3cab5e557a15dd3fa7197098d6b0abcc01fab..5d63cf2c230b4368e8a84e52413d37da26fb279a 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -566,13 +566,13 @@ static size_t net_dm_packet_report_size(size_t payload_len)
 	       /* NET_DM_ATTR_ORIGIN */
 	       nla_total_size(sizeof(u16)) +
 	       /* NET_DM_ATTR_PC */
-	       nla_total_size(sizeof(u64)) +
+	       nla_total_size_64bit(sizeof(u64)) +
 	       /* NET_DM_ATTR_SYMBOL */
 	       nla_total_size(NET_DM_MAX_SYMBOL_LEN + 1) +
 	       /* NET_DM_ATTR_IN_PORT */
 	       net_dm_in_port_size() +
 	       /* NET_DM_ATTR_TIMESTAMP */
-	       nla_total_size(sizeof(u64)) +
+	       nla_total_size_64bit(sizeof(u64)) +
 	       /* NET_DM_ATTR_ORIG_LEN */
 	       nla_total_size(sizeof(u32)) +
 	       /* NET_DM_ATTR_PROTO */
@@ -768,7 +768,7 @@ net_dm_hw_packet_report_size(size_t payload_len,
 	       /* NET_DM_ATTR_FLOW_ACTION_COOKIE */
 	       net_dm_flow_action_cookie_size(hw_metadata) +
 	       /* NET_DM_ATTR_TIMESTAMP */
-	       nla_total_size(sizeof(u64)) +
+	       nla_total_size_64bit(sizeof(u64)) +
 	       /* NET_DM_ATTR_ORIG_LEN */
 	       nla_total_size(sizeof(u32)) +
 	       /* NET_DM_ATTR_PROTO */
-- 
2.55.0.229.g6434b31f56-goog

[PATCH v2 net 2/2] drop_monitor: perform u64_stats updates under IRQ-disabled section

[Eric Dumazet]

In net_dm_packet_trace_kfree_skb_hit() and net_dm_hw_trap_packet_probe(),
u64_stats_update_begin() / u64_stats_inc() / u64_stats_update_end() were
called after spin_unlock_irqrestore(&...drop_queue.lock, flags), when local
IRQs had already been re-enabled.

Tracepoint probes can execute in IRQ or softirq context. On 32-bit
architectures, u64_stats_update_begin() disables preemption but not interrupts,
relying on seqcount writes. If a nested interrupt occurs on the same CPU during
the 64-bit stats update, the reentrant seqcount update can corrupt the
seqcount state or stats value.

Fix this by performing the 64-bit per-CPU stats update before releasing
drop_queue.lock via spin_unlock_irqrestore(), ensuring local interrupts remain
disabled during the u64_stats update.

Fixes: e9feb58020f9 ("drop_monitor: Expose tail drop counter")
Fixes: 5e58109b1ea4 ("drop_monitor: Add support for packet alert mode for hardware drops")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/core/drop_monitor.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 5d63cf2c230b4368e8a84e52413d37da26fb279a..8800a21ded084025bd1a4e5365de9971ab660808 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -530,10 +530,10 @@ static void net_dm_packet_trace_kfree_skb_hit(void *ignore,
 	return;
 
 unlock_free:
-	spin_unlock_irqrestore(&data->drop_queue.lock, flags);
 	u64_stats_update_begin(&data->stats.syncp);
 	u64_stats_inc(&data->stats.dropped);
 	u64_stats_update_end(&data->stats.syncp);
+	spin_unlock_irqrestore(&data->drop_queue.lock, flags);
 	consume_skb(nskb);
 }
 
@@ -1001,10 +1001,10 @@ net_dm_hw_trap_packet_probe(void *ignore, const struct devlink *devlink,
 	return;
 
 unlock_free:
-	spin_unlock_irqrestore(&hw_data->drop_queue.lock, flags);
 	u64_stats_update_begin(&hw_data->stats.syncp);
 	u64_stats_inc(&hw_data->stats.dropped);
 	u64_stats_update_end(&hw_data->stats.syncp);
+	spin_unlock_irqrestore(&hw_data->drop_queue.lock, flags);
 	net_dm_hw_metadata_free(n_hw_metadata);
 free:
 	consume_skb(nskb);
-- 
2.55.0.229.g6434b31f56-goog