CVE-2026-52910

In the Linux kernel, the following vulnerability has been resolved:

bpf: Free reuseport cBPF prog after RCU grace period.

Eulgyu Kim reported the splat below with a repro. [0]

The repro sets up a UDP reuseport group with a cBPF prog and

replaces it with a new one while another thread is sending

a UDP packet to the group.

The reuseport prog is freed by sk_reuseport_prog_free().

bpf_prog_put() is called for "e"BPF prog to destruct through

multiple stages while cBPF prog is freed immediately by

bpf_release_orig_filter() and bpf_prog_free().

If a reuseport prog is detached from the setsockopt() path

(reuseport_attach_prog() or reuseport_detach_prog()),

sk_reuseport_prog_free() is called without waiting for RCU

readers to complete, resulting in various bugs.

Let's defer freeing the reuseport cBPF prog after one RCU

grace period.

Note "e"BPF prog is safe as is unless the fast path starts

to touch fields destroyed in bpf_prog_put_deferred() and

__bpf_prog_put_noref().

[0]:

BUG: KASAN: vmalloc-out-of-bounds in reuseport_select_sock+0xedc/0x1220 net/core/sock_reuseport.c:596

Read of size 4 at addr ffffc9000051e004 by task slowme/10208

CPU: 6 UID: 1000 PID: 10208 Comm: slowme Not tainted 7.0.0-geb7ac95ff75e #32 PREEMPT(full)

Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014

Call Trace:

<IRQ>

dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120

print_address_description mm/kasan/report.c:378 [inline]

print_report+0xca/0x240 mm/kasan/report.c:482

kasan_report+0x118/0x150 mm/kasan/report.c:595

reuseport_select_sock+0xedc/0x1220 net/core/sock_reuseport.c:596

udp4_lib_lookup2+0x3bc/0x950 net/ipv4/udp.c:495

__udp4_lib_lookup+0x768/0xe20 net/ipv4/udp.c:723

__udp4_lib_lookup_skb+0x297/0x390 net/ipv4/udp.c:752

__udp4_lib_rcv+0x1312/0x2620 net/ipv4/udp.c:2752

ip_protocol_deliver_rcu+0x282/0x440 net/ipv4/ip_input.c:207

ip_local_deliver_finish+0x3bb/0x6f0 net/ipv4/ip_input.c:241

NF_HOOK+0x30c/0x3a0 include/linux/netfilter.h:318

NF_HOOK+0x30c/0x3a0 include/linux/netfilter.h:318

__netif_receive_skb_one_core net/core/dev.c:6181 [inline]

__netif_receive_skb net/core/dev.c:6294 [inline]

process_backlog+0xaa4/0x1960 net/core/dev.c:6645

__napi_poll+0xae/0x340 net/core/dev.c:7709

napi_poll net/core/dev.c:7772 [inline]

net_rx_action+0x5d7/0xf50 net/core/dev.c:7929

handle_softirqs+0x22b/0x870 kernel/softirq.c:622

do_softirq+0x76/0xd0 kernel/softirq.c:523

</IRQ>

<TASK>

__local_bh_enable_ip+0xf8/0x130 kernel/softirq.c:450

local_bh_enable include/linux/bottom_half.h:33 [inline]

rcu_read_unlock_bh include/linux/rcupdate.h:924 [inline]

__dev_queue_xmit+0x1dd7/0x3710 net/core/dev.c:4890

neigh_output include/net/neighbour.h:556 [inline]

ip_finish_output2+0xca9/0x1070 net/ipv4/ip_output.c:237

NF_HOOK_COND include/linux/netfilter.h:307 [inline]

ip_output+0x29f/0x450 net/ipv4/ip_output.c:438

ip_send_skb+0x45/0xc0 net/ipv4/ip_output.c:1508

udp_send_skb+0xb04/0x1510 net/ipv4/udp.c:1195

udp_sendmsg+0x1a71/0x2350 net/ipv4/udp.c:1485

sock_sendmsg_nosec net/socket.c:727 [inline]

__sock_sendmsg net/socket.c:742 [inline]

__sys_sendto+0x554/0x680 net/socket.c:2206

__do_sys_sendto net/socket.c:2213 [inline]

__se_sys_sendto net/socket.c:2209 [inline]

__x64_sys_sendto+0xde/0x100 net/socket.c:2209

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]

do_syscall_64+0x160/0xf80 arch/x86/entry/syscall_64.c:94

entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x415a2d

Code: b3 66 2e 0f 1f 84 00 00 00 00 00 66 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007f6bc31e41e8 EFLAGS: 00000212 ORIG_RAX: 000000000000002c

RAX: ffffffffffffffda RBX: 00007f6bc31e4cdc RCX: 0000000000415a2d

RDX: 0000000000000001 RSI: 00007f6bc31e421f RDI: 0000000000000003

RBP: 00007f6bc31e4240 R08: 00007f6bc31e4220 R09: 0000000000000010

R10: 0000000000000000 R11:

---truncated---