linux.git/drivers/net/veth.c, branch v7.2 Linux kernel source tree veth: fix queue index used to wake the peer txq in veth_poll 2026-08-10T22:57:47+00:00 Jonas Köppeler j.koeppeler@tu-berlin.de 2026-08-06T11:43:49+00:00 60db47f02bfa2aa688938aa199117ec4f8e31d23 veth_poll() derives the index of the peer TX queue to wake from rq->xdp_rxq.queue_index. That field is only initialized by xdp_rxq_info_reg() in veth_enable_xdp_range(), which runs only when an XDP program is attached. On the plain GRO/NAPI path (veth_napi_enable_range()) xdp_rxq_info_reg() is never called, so queue_index stays 0 for every queue, as priv->rq is zero-allocated. So in a multi-queue setup with GRO enabled and no XDP program attached, every NAPI instance looks at the peer's TX queue 0. If veth_xmit() stops peer TX queue 1 because the ptr_ring is full (NETDEV_TX_BUSY), nothing ever wakes it again: the poller draining queue 1 wakes queue 0 instead. veth implements no ndo_tx_timeout, so the netdev watchdog does not kick in either, and the queue stays stopped indefinitely. Derive the index from the position of the rq within priv->rq instead, which is correct regardless of whether XDP was ever enabled. Scripts to reproduce the stall are available at https://github.com/netoptimizer/veth-backpressure-performance-testing Fixes: dc82a33297fc ("veth: apply qdisc backpressure on full ptr_ring to reduce TX drops") Signed-off-by: Jonas Köppeler <j.koeppeler@tu-berlin.de> Tested-by: Jesper Dangaard Brouer <hawk@kernel.org> Acked-by: Jesper Dangaard Brouer <hawk@kernel.org> Link: https://patch.msgid.link/20260806-veth-fix-poll-queue-idx-v1-1-c5357fb7573d@tu-berlin.de Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
veth_poll() derives the index of the peer TX queue to wake from
rq->xdp_rxq.queue_index. That field is only initialized by
xdp_rxq_info_reg() in veth_enable_xdp_range(), which runs only when an
XDP program is attached. On the plain GRO/NAPI path
(veth_napi_enable_range()) xdp_rxq_info_reg() is never called, so
queue_index stays 0 for every queue, as priv->rq is zero-allocated.

So in a multi-queue setup with GRO enabled and no XDP program attached,
every NAPI instance looks at the peer's TX queue 0. If veth_xmit() stops
peer TX queue 1 because the ptr_ring is full (NETDEV_TX_BUSY), nothing
ever wakes it again: the poller draining queue 1 wakes queue 0 instead.
veth implements no ndo_tx_timeout, so the netdev watchdog does not kick
in either, and the queue stays stopped indefinitely.

Derive the index from the position of the rq within priv->rq instead,
which is correct regardless of whether XDP was ever enabled.

Scripts to reproduce the stall are available at
https://github.com/netoptimizer/veth-backpressure-performance-testing

Fixes: dc82a33297fc ("veth: apply qdisc backpressure on full ptr_ring to reduce TX drops")
Signed-off-by: Jonas Köppeler <j.koeppeler@tu-berlin.de>
Tested-by: Jesper Dangaard Brouer <hawk@kernel.org>
Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>
Link: https://patch.msgid.link/20260806-veth-fix-poll-queue-idx-v1-1-c5357fb7573d@tu-berlin.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
veth: fix skb length accounting after XDP frag adjustment 2026-08-08T00:01:05+00:00 Sun Jian sun.jian.kdev@gmail.com 2026-08-04T05:40:39+00:00 cb6379feaaff11c4e1e79c26c745ffa23182768a veth exposes non-linear skb fragments through an xdp_buff. If an XDP program adjusts the fragment area, veth_xdp_rcv_skb() copies xdp_frags_size back to skb->data_len but leaves skb->len containing the old fragment contribution. After a fragment shrink, this makes skb_headlen() larger than the actual linear area. In the reproduced UDP receive path, __skb_datagram_iter() copied 1024 bytes past the actual linear tail to userspace, starting at struct skb_shared_info. The copied bytes included the affected skb's nr_frags, xdp_frags_size, and a kernel pointer from skb_shinfo(skb)->frags[0]. Real packet data was displaced by the same amount and truncated at the end. Subtract the old data_len before replacing it and add the new data_len afterwards, keeping skb->len and skb->data_len synchronized. Additionally, bpf_xdp_pull_data() can advance data_end while leaving frags present. The skb is then still non-linear, so the old __skb_put(skb, off) triggers SKB_LINEAR_ASSERT(). Use skb_set_tail_pointer() and update skb->len explicitly instead, following bpf_prog_run_generic_xdp(). Unlike __skb_put(), skb_set_tail_pointer() does not require a linear skb. A 60000-byte UDP datagram on a veth pair with MTU 64000 was shortened by 1024 bytes from its fragment area. Before the fix, all 10 runs produced corrupted payloads. After the fix, all 10 runs matched the expected payload exactly. A forced-tailroom reproducer also exercises bpf_xdp_pull_data() with frags still present; the old code triggers SKB_LINEAR_ASSERT(), while this fix passes 10/10 runs. Fixes: 718a18a0c8a6 ("veth: Rework veth_xdp_rcv_skb in order to accept non-linear skb") Cc: stable@vger.kernel.org Reported-by: Mohsin Bashir <mohsin.bashr@gmail.com> Link: https://lore.kernel.org/bpf/80687d9c-9c27-494c-b3f2-efd0230b1895@gmail.com/ Suggested-by: Lorenzo Bianconi <lorenzo@kernel.org> Acked-by: Lorenzo Bianconi <lorenzo@kernel.org> Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com> Link: https://patch.msgid.link/20260804054040.613675-3-sun.jian.kdev@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
veth exposes non-linear skb fragments through an xdp_buff. If an XDP
program adjusts the fragment area, veth_xdp_rcv_skb() copies
xdp_frags_size back to skb->data_len but leaves skb->len containing the
old fragment contribution.

After a fragment shrink, this makes skb_headlen() larger than the actual
linear area. In the reproduced UDP receive path, __skb_datagram_iter()
copied 1024 bytes past the actual linear tail to userspace, starting at
struct skb_shared_info. The copied bytes included the affected skb's
nr_frags, xdp_frags_size, and a kernel pointer from
skb_shinfo(skb)->frags[0]. Real packet data was displaced by the same
amount and truncated at the end.

Subtract the old data_len before replacing it and add the new data_len
afterwards, keeping skb->len and skb->data_len synchronized.

Additionally, bpf_xdp_pull_data() can advance data_end while leaving
frags present. The skb is then still non-linear, so the old
__skb_put(skb, off) triggers SKB_LINEAR_ASSERT().

Use skb_set_tail_pointer() and update skb->len explicitly instead,
following bpf_prog_run_generic_xdp(). Unlike __skb_put(),
skb_set_tail_pointer() does not require a linear skb.

A 60000-byte UDP datagram on a veth pair with MTU 64000 was shortened by
1024 bytes from its fragment area. Before the fix, all 10 runs produced
corrupted payloads. After the fix, all 10 runs matched the expected
payload exactly. A forced-tailroom reproducer also exercises
bpf_xdp_pull_data() with frags still present; the old code triggers
SKB_LINEAR_ASSERT(), while this fix passes 10/10 runs.

Fixes: 718a18a0c8a6 ("veth: Rework veth_xdp_rcv_skb in order to accept non-linear skb")
Cc: stable@vger.kernel.org
Reported-by: Mohsin Bashir <mohsin.bashr@gmail.com>
Link: https://lore.kernel.org/bpf/80687d9c-9c27-494c-b3f2-efd0230b1895@gmail.com/
Suggested-by: Lorenzo Bianconi <lorenzo@kernel.org>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com>
Link: https://patch.msgid.link/20260804054040.613675-3-sun.jian.kdev@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
veth: convert frag_list skbs before running XDP 2026-07-25T00:02:10+00:00 Matt Fleming mfleming@cloudflare.com 2026-07-22T19:19:25+00:00 d0d6415963040c401e7a7e4e482a698ba52448cb A frag_list skb can reach veth with data_len set but nr_frags zero. veth_convert_skb_to_xdp_buff() only converts skbs that are shared, locked, have frags[], or do not have enough headroom. It later uses skb_is_nonlinear() to decide whether to set XDP_FLAGS_HAS_FRAGS and xdp_frags_size. That exposes frag_list data to XDP as if it were stored in frags[], but frags[] is empty. AF_XDP copy mode can then trust the bogus XDP fragment metadata, walk an empty fragment entry, and crash in memcpy() from __xsk_rcv(). Route non-linear skbs through skb_pp_cow_data() before exposing them to XDP, and only advertise XDP frags when the resulting skb has frags[]. skb_copy_bits() already handles frag_list input, and skb_pp_cow_data() builds frags[] output with skb_add_rx_frag(), which is the representation XDP multi-buffer expects. Fixes: 718a18a0c8a6 ("veth: Rework veth_xdp_rcv_skb in order to accept non-linear skb") Cc: stable@vger.kernel.org Signed-off-by: Matt Fleming <mfleming@cloudflare.com> Reviewed-by: Toke Høiland-Jørgensen <toke@toke.dk> Acked-by: Lorenzo Bianconi <lorenzo@kernel.org> Link: https://patch.msgid.link/20260722191925.2192070-1-matt@readmodwrite.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
A frag_list skb can reach veth with data_len set but nr_frags zero.
veth_convert_skb_to_xdp_buff() only converts skbs that are shared,
locked, have frags[], or do not have enough headroom. It later uses
skb_is_nonlinear() to decide whether to set XDP_FLAGS_HAS_FRAGS and
xdp_frags_size.

That exposes frag_list data to XDP as if it were stored in frags[], but
frags[] is empty. AF_XDP copy mode can then trust the bogus XDP fragment
metadata, walk an empty fragment entry, and crash in memcpy() from
__xsk_rcv().

Route non-linear skbs through skb_pp_cow_data() before exposing them to
XDP, and only advertise XDP frags when the resulting skb has frags[].
skb_copy_bits() already handles frag_list input, and skb_pp_cow_data()
builds frags[] output with skb_add_rx_frag(), which is the
representation XDP multi-buffer expects.

Fixes: 718a18a0c8a6 ("veth: Rework veth_xdp_rcv_skb in order to accept non-linear skb")
Cc: stable@vger.kernel.org
Signed-off-by: Matt Fleming <mfleming@cloudflare.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@toke.dk>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20260722191925.2192070-1-matt@readmodwrite.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
veth: fix NAPI leak in XDP enable error path 2026-06-23T21:46:32+00:00 Eric Dumazet edumazet@google.com 2026-06-22T11:18:25+00:00 6739027cb72da26890edd424c77080d187b2a92e During XDP enablement in veth, if xdp_rxq_info_reg() or xdp_rxq_info_reg_mem_model() fails, the driver rolls back the changes. However, the rollback loop: for (i--; i >= start; i--) { decrements the loop index 'i' before the first iteration. This correctly skips unregistering the rxq for the failed index 'i' (as registration failed or was already cleaned up), but it also erroneously skips calling netif_napi_deli() for rq[i].xdp_napi. Since netif_napi_add() was already called for index 'i', this leaves a dangling napi_struct in the device's napi_list. When the veth device is later destroyed, the freed queue memory (which contains the leaked NAPI structure) can be reused. The subsequent device teardown iterates the NAPI list and corrupts the reallocated memory, leading to UAF. Fix this by explicitly deleting the NAPI association for the failed index 'i' before rolling back the successfully configured queues. Fixes: b02e5a0ebb17 ("xsk: Propagate napi_id to XDP socket Rx path") Reported-by: Guenter Roeck <groeck@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Daniel Borkmann <daniel@iogearbox.net> Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org> Cc: Michael S. Tsirkin <mst@redhat.com> Cc: Tariq Toukan <tariqt@nvidia.com> Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com> Link: https://patch.msgid.link/20260622111825.88337-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
During XDP enablement in veth, if xdp_rxq_info_reg() or
xdp_rxq_info_reg_mem_model() fails, the driver rolls back the changes.

However, the rollback loop:
	for (i--; i >= start; i--) {

decrements the loop index 'i' before the first iteration. This
correctly skips unregistering the rxq for the failed index 'i' (as
registration failed or was already cleaned up), but it also
erroneously skips calling netif_napi_deli() for rq[i].xdp_napi.

Since netif_napi_add() was already called for index 'i', this leaves
a dangling napi_struct in the device's napi_list. When the veth
device is later destroyed, the freed queue memory (which contains the
leaked NAPI structure) can be reused.

The subsequent device teardown iterates the NAPI list and
corrupts the reallocated memory, leading to UAF.

Fix this by explicitly deleting the NAPI association for the failed
index 'i' before rolling back the successfully configured queues.

Fixes: b02e5a0ebb17 ("xsk: Propagate napi_id to XDP socket Rx path")
Reported-by: Guenter Roeck <groeck@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Björn Töpel <bjorn.topel@intel.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Link: https://patch.msgid.link/20260622111825.88337-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
veth: fix OOB txq access in veth_poll() with asymmetric queue counts 2026-05-07T14:24:07+00:00 Jesper Dangaard Brouer hawk@kernel.org 2026-05-05T13:21:53+00:00 08f566e8f83bb70f04ad5aba5be352c490a01c8a XDP redirect into a veth device (via bpf_redirect()) calls veth_xdp_xmit(), which enqueues frames into the peer's ptr_ring using smp_processor_id() % peer->real_num_rx_queues as the ring index. With an asymmetric veth pair where the peer has fewer TX queues than RX queues, that index can exceed peer->real_num_tx_queues. veth_poll() then resolves peer_txq for the ring via: peer_txq = peer_dev ? netdev_get_tx_queue(peer_dev, queue_idx) : NULL; where queue_idx = rq->xdp_rxq.queue_index. When queue_idx exceeds peer_dev->real_num_tx_queues this is an out-of-bounds (OOB) access into the peer's netdev_queue array, triggering DEBUG_NET_WARN_ON_ONCE in netdev_get_tx_queue(). The normal ndo_start_xmit path is not affected: the stack clamps skb->queue_mapping via netdev_cap_txqueue() before invoking ndo_start_xmit, so rxq in veth_xmit() never exceeds real_num_tx_queues. Fix veth_poll() by clamping: only dereference peer_txq when queue_idx is within bounds, otherwise set it to NULL. The out-of-range rings are fed exclusively via XDP redirect (veth_xdp_xmit), never via ndo_start_xmit (veth_xmit), so the peer txq was never stopped and there is nothing to wake; NULL is the correct fallback. Reported-by: Sashiko <sashiko-bot@kernel.org> Closes: https://lore.kernel.org/all/20260502071828.616C3C19425@smtp.kernel.org/ Fixes: dc82a33297fc ("veth: apply qdisc backpressure on full ptr_ring to reduce TX drops") Signed-off-by: Jesper Dangaard Brouer <hawk@kernel.org> Link: https://patch.msgid.link/20260505132159.241305-2-hawk@kernel.org Signed-off-by: Paolo Abeni <pabeni@redhat.com> 
XDP redirect into a veth device (via bpf_redirect()) calls
veth_xdp_xmit(), which enqueues frames into the peer's ptr_ring using
  smp_processor_id() % peer->real_num_rx_queues
as the ring index.  With an asymmetric veth pair where the peer has
fewer TX queues than RX queues, that index can exceed
peer->real_num_tx_queues.

veth_poll() then resolves peer_txq for the ring via:

  peer_txq = peer_dev ? netdev_get_tx_queue(peer_dev, queue_idx) : NULL;

where queue_idx = rq->xdp_rxq.queue_index.  When queue_idx exceeds
peer_dev->real_num_tx_queues this is an out-of-bounds (OOB) access
into the peer's netdev_queue array, triggering DEBUG_NET_WARN_ON_ONCE
in netdev_get_tx_queue().

The normal ndo_start_xmit path is not affected: the stack clamps
skb->queue_mapping via netdev_cap_txqueue() before invoking
ndo_start_xmit, so rxq in veth_xmit() never exceeds real_num_tx_queues.

Fix veth_poll() by clamping: only dereference peer_txq when queue_idx is
within bounds, otherwise set it to NULL.  The out-of-range rings are fed
exclusively via XDP redirect (veth_xdp_xmit), never via ndo_start_xmit
(veth_xmit), so the peer txq was never stopped and there is nothing to
wake; NULL is the correct fallback.

Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/20260502071828.616C3C19425@smtp.kernel.org/
Fixes: dc82a33297fc ("veth: apply qdisc backpressure on full ptr_ring to reduce TX drops")
Signed-off-by: Jesper Dangaard Brouer <hawk@kernel.org>
Link: https://patch.msgid.link/20260505132159.241305-2-hawk@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21T09:02:28+00:00 Kees Cook kees@kernel.org 2026-02-21T07:49:23+00:00 69050f8d6d075dc01af7a5f2f550a8067510366f This is the result of running the Coccinelle script from scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to avoid scalar types (which need careful case-by-case checking), and instead replace kmalloc-family calls that allocate struct or union object instances: Single allocations: kmalloc(sizeof(TYPE), ...) are replaced with: kmalloc_obj(TYPE, ...) Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...) are replaced with: kmalloc_objs(TYPE, COUNT, ...) Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...) are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...) (where TYPE may also be *VAR) The resulting allocations no longer return "void *", instead returning "TYPE *". Signed-off-by: Kees Cook <kees@kernel.org> 
This is the result of running the Coccinelle script from
scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to
avoid scalar types (which need careful case-by-case checking), and
instead replace kmalloc-family calls that allocate struct or union
object instances:

Single allocations:	kmalloc(sizeof(TYPE), ...)
are replaced with:	kmalloc_obj(TYPE, ...)

Array allocations:	kmalloc_array(COUNT, sizeof(TYPE), ...)
are replaced with:	kmalloc_objs(TYPE, COUNT, ...)

Flex array allocations:	kmalloc(struct_size(PTR, FAM, COUNT), ...)
are replaced with:	kmalloc_flex(*PTR, FAM, COUNT, ...)

(where TYPE may also be *VAR)

The resulting allocations no longer return "void *", instead returning
"TYPE *".

Signed-off-by: Kees Cook <kees@kernel.org>
veth: fix data race in veth_get_ethtool_stats 2026-01-18T00:22:18+00:00 David Yang mmyangfl@gmail.com 2026-01-14T12:24:45+00:00 b47adaab8b3d443868096bac08fdbb3d403194ba In veth_get_ethtool_stats(), some statistics protected by u64_stats_sync, are read and accumulated in ignorance of possible u64_stats_fetch_retry() events. These statistics, peer_tq_xdp_xmit and peer_tq_xdp_xmit_err, are already accumulated by veth_xdp_xmit(). Fix this by reading them into a temporary buffer first. Fixes: 5fe6e56776ba ("veth: rely on peer veth_rq for ndo_xdp_xmit accounting") Signed-off-by: David Yang <mmyangfl@gmail.com> Link: https://patch.msgid.link/20260114122450.227982-1-mmyangfl@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
In veth_get_ethtool_stats(), some statistics protected by
u64_stats_sync, are read and accumulated in ignorance of possible
u64_stats_fetch_retry() events. These statistics, peer_tq_xdp_xmit and
peer_tq_xdp_xmit_err, are already accumulated by veth_xdp_xmit(). Fix
this by reading them into a temporary buffer first.

Fixes: 5fe6e56776ba ("veth: rely on peer veth_rq for ndo_xdp_xmit accounting")
Signed-off-by: David Yang <mmyangfl@gmail.com>
Link: https://patch.msgid.link/20260114122450.227982-1-mmyangfl@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2025-11-27T20:19:08+00:00 Jakub Kicinski kuba@kernel.org 2025-11-27T20:16:40+00:00 db4029859d6fd03f0622d394f4cdb1be86d7ec62 Conflicts: net/xdp/xsk.c 0ebc27a4c67d ("xsk: avoid data corruption on cq descriptor number") 8da7bea7db69 ("xsk: add indirect call for xsk_destruct_skb") 30ed05adca4a ("xsk: use a smaller new lock for shared pool case") https://lore.kernel.org/20251127105450.4a1665ec@canb.auug.org.au https://lore.kernel.org/eb4eee14-7e24-4d1b-b312-e9ea738fefee@kernel.org Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
Conflicts:

net/xdp/xsk.c
  0ebc27a4c67d ("xsk: avoid data corruption on cq descriptor number")
  8da7bea7db69 ("xsk: add indirect call for xsk_destruct_skb")
  30ed05adca4a ("xsk: use a smaller new lock for shared pool case")
https://lore.kernel.org/20251127105450.4a1665ec@canb.auug.org.au
https://lore.kernel.org/eb4eee14-7e24-4d1b-b312-e9ea738fefee@kernel.org

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
veth: reduce XDP no_direct return section to fix race 2025-11-21T02:44:32+00:00 Jesper Dangaard Brouer hawk@kernel.org 2025-11-19T16:28:36+00:00 a14602fcae17a3f1cb8a8521bedf31728f9e7e39 As explain in commit fa349e396e48 ("veth: Fix race with AF_XDP exposing old or uninitialized descriptors") for veth there is a chance after napi_complete_done() that another CPU can manage start another NAPI instance running veth_pool(). For NAPI this is correctly handled as the napi_schedule_prep() check will prevent multiple instances from getting scheduled, but for the remaining code in veth_pool() this can run concurrent with the newly started NAPI instance. The problem/race is that xdp_clear_return_frame_no_direct() isn't designed to be nested. Prior to commit 401cb7dae813 ("net: Reference bpf_redirect_info via task_struct on PREEMPT_RT.") the temporary BPF net context bpf_redirect_info was stored per CPU, where this wasn't an issue. Since this commit the BPF context is stored in 'current' task_struct. When running veth in threaded-NAPI mode, then the kthread becomes the storage area. Now a race exists between two concurrent veth_pool() function calls one exiting NAPI and one running new NAPI, both using the same BPF net context. Race is when another CPU gets within the xdp_set_return_frame_no_direct() section before exiting veth_pool() calls the clear-function xdp_clear_return_frame_no_direct(). Fixes: 401cb7dae8130 ("net: Reference bpf_redirect_info via task_struct on PREEMPT_RT.") Signed-off-by: Jesper Dangaard Brouer <hawk@kernel.org> Link: https://patch.msgid.link/176356963888.337072.4805242001928705046.stgit@firesoul Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
As explain in commit fa349e396e48 ("veth: Fix race with AF_XDP exposing
old or uninitialized descriptors") for veth there is a chance after
napi_complete_done() that another CPU can manage start another NAPI
instance running veth_pool(). For NAPI this is correctly handled as the
napi_schedule_prep() check will prevent multiple instances from getting
scheduled, but for the remaining code in veth_pool() this can run
concurrent with the newly started NAPI instance.

The problem/race is that xdp_clear_return_frame_no_direct() isn't
designed to be nested.

Prior to commit 401cb7dae813 ("net: Reference bpf_redirect_info via
task_struct on PREEMPT_RT.") the temporary BPF net context
bpf_redirect_info was stored per CPU, where this wasn't an issue. Since
this commit the BPF context is stored in 'current' task_struct. When
running veth in threaded-NAPI mode, then the kthread becomes the storage
area. Now a race exists between two concurrent veth_pool() function calls
one exiting NAPI and one running new NAPI, both using the same BPF net
context.

Race is when another CPU gets within the xdp_set_return_frame_no_direct()
section before exiting veth_pool() calls the clear-function
xdp_clear_return_frame_no_direct().

Fixes: 401cb7dae8130 ("net: Reference bpf_redirect_info via task_struct on PREEMPT_RT.")
Signed-off-by: Jesper Dangaard Brouer <hawk@kernel.org>
Link: https://patch.msgid.link/176356963888.337072.4805242001928705046.stgit@firesoul
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2025-11-20T17:13:26+00:00 Jakub Kicinski kuba@kernel.org 2025-11-20T17:12:41+00:00 9e203721ec6117b2f4436a26662413764fd669f0 Cross-merge networking fixes after downstream PR (net-6.18-rc7). No conflicts, adjacent changes: tools/testing/selftests/net/af_unix/Makefile e1bb28bf13f4 ("selftest: af_unix: Add test for SO_PEEK_OFF.") 45a1cd8346ca ("selftests: af_unix: Add tests for ECONNRESET and EOF semantics") Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
Cross-merge networking fixes after downstream PR (net-6.18-rc7).

No conflicts, adjacent changes:

tools/testing/selftests/net/af_unix/Makefile
  e1bb28bf13f4 ("selftest: af_unix: Add test for SO_PEEK_OFF.")
  45a1cd8346ca ("selftests: af_unix: Add tests for ECONNRESET and EOF semantics")

Signed-off-by: Jakub Kicinski <kuba@kernel.org>