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net: devmem: refresh devmem TX dst in case of route invalidation

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The zero-copy Device Memory (Devmem) transmit path
relies on the socket's route cache (`dst_entry`) to
validate that the packet is being sent via the network
device to which the DMA buffer was bound.

However, this check incorrectly fails and returns `-ENODEV`
if the socket's route cache entry (`dst`) is merely missing
or expired (`dst == NULL`). This scenario is observed during
network events, such as when flow steering rules are deleted,
leading to a temporary route cache invalidation.

This patch fixes -ENODEV error for `net_devmem_get_binding()`
by doing the following:

1.  It attempts to rebuild the route via `rebuild_header()`
if the route is initially missing (`dst == NULL`). This
allows the TCP/IP stack to recover from transient route
cache misses.
2.  It uses `rcu_read_lock()` and `dst_dev_rcu()` to safely
access the network device pointer (`dst_dev`) from the
route, preventing use-after-free conditions if the
device is concurrently removed.
3.  It maintains the critical safety check by validating
that the retrieved destination device (`dst_dev`) is
exactly the device registered in the Devmem binding
(`binding->dev`).

These changes prevent unnecessary ENODEV failures while
maintaining the critical safety requirement that the
Devmem resources are only used on the bound network device.

Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>
Reported-by: Eric Dumazet <edumazet@google.com>
Reported-by: Vedant Mathur <vedantmathur@google.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Fixes: bd61848900 ("net: devmem: Implement TX path")
Signed-off-by: Shivaji Kant <shivajikant@google.com>
Link: https://patch.msgid.link/20251029065420.3489943-1-shivajikant@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Shivaji Kant
2025-10-29 06:54:19 +00:00
committed by Jakub Kicinski
parent a38eeecfe3
commit 6a2108c780
1 changed files with 24 additions and 3 deletions
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27
net/core/devmem.c
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@@ -17,6 +17,7 @@
#include <net/page_pool/helpers.h>
#include <net/page_pool/memory_provider.h>
#include <net/sock.h>
#include <net/tcp.h>
#include <trace/events/page_pool.h>
#include "devmem.h"
@@ -357,7 +358,8 @@ struct net_devmem_dmabuf_binding *net_devmem_get_binding(struct sock *sk,
unsigned int dmabuf_id)
{
struct net_devmem_dmabuf_binding *binding;
struct dst_entry *dst = __sk_dst_get(sk);
struct net_device *dst_dev;
struct dst_entry *dst;
int err = 0;
binding = net_devmem_lookup_dmabuf(dmabuf_id);
@@ -366,16 +368,35 @@ struct net_devmem_dmabuf_binding *net_devmem_get_binding(struct sock *sk,
goto out_err;
}
rcu_read_lock();
dst = __sk_dst_get(sk);
/* If dst is NULL (route expired), attempt to rebuild it. */
if (unlikely(!dst)) {
if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk)) {
err = -EHOSTUNREACH;
goto out_unlock;
}
dst = __sk_dst_get(sk);
if (unlikely(!dst)) {
err = -ENODEV;
goto out_unlock;
}
}
/* The dma-addrs in this binding are only reachable to the corresponding
* net_device.
*/
if (!dst || !dst->dev || dst->dev->ifindex != binding->dev->ifindex) {
dst_dev = dst_dev_rcu(dst);
if (unlikely(!dst_dev) || unlikely(dst_dev != binding->dev)) {
err = -ENODEV;
goto out_err;
goto out_unlock;
}
rcu_read_unlock();
return binding;
out_unlock:
rcu_read_unlock();
out_err:
if (binding)
net_devmem_dmabuf_binding_put(binding);