veth: reduce XDP no_direct return section to fix race

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[ Upstream commit a14602fcae ]

As explain in commit fa349e396e ("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 401cb7dae8 ("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: 401cb7dae8 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

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This commit is contained in:

Jesper Dangaard Brouer 2025-11-19 17:28:36 +01:00 • committed by Greg Kroah-Hartman

parent dd419a3f2e

commit c1ceabcb34

1 changed files with 3 additions and 4 deletions

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drivers/net/veth.c

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