CVE-2026-52910: bpf: Free reuseport cBPF prog after RCU grace period.

CVE-2026-52910: bpf: Free reuseport cBPF prog after RCU grace period.

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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: 0000000000000212 R12: 00007f6bc31e46c0
R13: ffffffffffffffb8 R14: 0000000000000000 R15: 00007ffc9b0d70b0
 </TASK>

The Linux kernel CVE team has assigned CVE-2026-52910 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.5 with commit 538950a1b7527a0a52ccd9337e3fcd304f027f13 and fixed in 5.10.259 with commit 08264d5bba0bdd3a79bc2984fee09286aba0c4eb
	Issue introduced in 4.5 with commit 538950a1b7527a0a52ccd9337e3fcd304f027f13 and fixed in 5.15.210 with commit fec41484e7c2aa7ded44c541bba98872be937754
	Issue introduced in 4.5 with commit 538950a1b7527a0a52ccd9337e3fcd304f027f13 and fixed in 6.1.176 with commit c3e3fddda6b5d9ba505d218b4055e7d8a282ac57
	Issue introduced in 4.5 with commit 538950a1b7527a0a52ccd9337e3fcd304f027f13 and fixed in 6.6.143 with commit f8b8f1d4bb76098e87b8269a0631019648330e6d
	Issue introduced in 4.5 with commit 538950a1b7527a0a52ccd9337e3fcd304f027f13 and fixed in 6.12.94 with commit 298db6167f81e9c470a57cf652e4e47757b4293e
	Issue introduced in 4.5 with commit 538950a1b7527a0a52ccd9337e3fcd304f027f13 and fixed in 6.18.36 with commit 87dfb977bdb6eaa47e9993a34e18f44970f88b1f
	Issue introduced in 4.5 with commit 538950a1b7527a0a52ccd9337e3fcd304f027f13 and fixed in 7.0.13 with commit 90e47dc5c572d1c73971ac51c7428803f42b78eb
	Issue introduced in 4.5 with commit 538950a1b7527a0a52ccd9337e3fcd304f027f13 and fixed in 7.1 with commit 18fc650ccd7fe3376eca89203668cfb8268f60df

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-52910
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/core/filter.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/08264d5bba0bdd3a79bc2984fee09286aba0c4eb
	https://git.kernel.org/stable/c/fec41484e7c2aa7ded44c541bba98872be937754
	https://git.kernel.org/stable/c/c3e3fddda6b5d9ba505d218b4055e7d8a282ac57
	https://git.kernel.org/stable/c/f8b8f1d4bb76098e87b8269a0631019648330e6d
	https://git.kernel.org/stable/c/298db6167f81e9c470a57cf652e4e47757b4293e
	https://git.kernel.org/stable/c/87dfb977bdb6eaa47e9993a34e18f44970f88b1f
	https://git.kernel.org/stable/c/90e47dc5c572d1c73971ac51c7428803f42b78eb
	https://git.kernel.org/stable/c/18fc650ccd7fe3376eca89203668cfb8268f60df