CVE-2025-38640 bpf: Disable migration in nf_hook_run_bpf().
In the Linux kernel, the following vulnerability has been resolved:

bpf: Disable migration in nf_hook_run_bpf().

syzbot reported that the netfilter bpf prog can be called without
migration disabled in xmit path.

Then the assertion in __bpf_prog_run() fails, triggering the splat
below. [0]

Let's use bpf_prog_run_pin_on_cpu() in nf_hook_run_bpf().

[0]:
BUG: assuming non migratable context at ./include/linux/filter.h:703
in_atomic(): 0, irqs_disabled(): 0, migration_disabled() 0 pid: 5829, name: sshd-session
3 locks held by sshd-session/5829:
 #0: ffff88807b4e4218 (sk_lock-AF_INET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1667 [inline]
 #0: ffff88807b4e4218 (sk_lock-AF_INET){+.+.}-{0:0}, at: tcp_sendmsg+0x20/0x50 net/ipv4/tcp.c:1395
 #1: ffffffff8e5c4e00 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #1: ffffffff8e5c4e00 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #1: ffffffff8e5c4e00 (rcu_read_lock){....}-{1:3}, at: __ip_queue_xmit+0x69/0x26c0 net/ipv4/ip_output.c:470
 #2: ffffffff8e5c4e00 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #2: ffffffff8e5c4e00 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #2: ffffffff8e5c4e00 (rcu_read_lock){....}-{1:3}, at: nf_hook+0xb2/0x680 include/linux/netfilter.h:241
CPU: 0 UID: 0 PID: 5829 Comm: sshd-session Not tainted 6.16.0-rc6-syzkaller-00002-g155a3c003e55 #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x16c/0x1f0 lib/dump_stack.c:120
 __cant_migrate kernel/sched/core.c:8860 [inline]
 __cant_migrate+0x1c7/0x250 kernel/sched/core.c:8834
 __bpf_prog_run include/linux/filter.h:703 [inline]
 bpf_prog_run include/linux/filter.h:725 [inline]
 nf_hook_run_bpf+0x83/0x1e0 net/netfilter/nf_bpf_link.c:20
 nf_hook_entry_hookfn include/linux/netfilter.h:157 [inline]
 nf_hook_slow+0xbb/0x200 net/netfilter/core.c:623
 nf_hook+0x370/0x680 include/linux/netfilter.h:272
 NF_HOOK_COND include/linux/netfilter.h:305 [inline]
 ip_output+0x1bc/0x2a0 net/ipv4/ip_output.c:433
 dst_output include/net/dst.h:459 [inline]
 ip_local_out net/ipv4/ip_output.c:129 [inline]
 __ip_queue_xmit+0x1d7d/0x26c0 net/ipv4/ip_output.c:527
 __tcp_transmit_skb+0x2686/0x3e90 net/ipv4/tcp_output.c:1479
 tcp_transmit_skb net/ipv4/tcp_output.c:1497 [inline]
 tcp_write_xmit+0x1274/0x84e0 net/ipv4/tcp_output.c:2838
 __tcp_push_pending_frames+0xaf/0x390 net/ipv4/tcp_output.c:3021
 tcp_push+0x225/0x700 net/ipv4/tcp.c:759
 tcp_sendmsg_locked+0x1870/0x42b0 net/ipv4/tcp.c:1359
 tcp_sendmsg+0x2e/0x50 net/ipv4/tcp.c:1396
 inet_sendmsg+0xb9/0x140 net/ipv4/af_inet.c:851
 sock_sendmsg_nosec net/socket.c:712 [inline]
 __sock_sendmsg net/socket.c:727 [inline]
 sock_write_iter+0x4aa/0x5b0 net/socket.c:1131
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x6c7/0x1150 fs/read_write.c:686
 ksys_write+0x1f8/0x250 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe7d365d407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP:
CVSS v3.1 score: 7.8