{ "schema_version": "1.6.1", "id": "RPI-CVE-2024-40958", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2024-40958" ], "published": "2024-07-12T12:32:42Z", "summary": "netns: Make get_net_ns() handle zero refcount net", "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetns: Make get_net_ns() handle zero refcount net\n\nSyzkaller hit a warning:\nrefcount_t: addition on 0; use-after-free.\nWARNING: CPU: 3 PID: 7890 at lib/refcount.c:25 refcount_warn_saturate+0xdf/0x1d0\nModules linked in:\nCPU: 3 PID: 7890 Comm: tun Not tainted 6.10.0-rc3-00100-gcaa4f9578aba-dirty #310\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014\nRIP: 0010:refcount_warn_saturate+0xdf/0x1d0\nCode: 41 49 04 31 ff 89 de e8 9f 1e cd fe 84 db 75 9c e8 76 26 cd fe c6 05 b6 41 49 04 01 90 48 c7 c7 b8 8e 25 86 e8 d2 05 b5 fe 90 <0f> 0b 90 90 e9 79 ff ff ff e8 53 26 cd fe 0f b6 1\nRSP: 0018:ffff8881067b7da0 EFLAGS: 00010286\nRAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff811c72ac\nRDX: ffff8881026a2140 RSI: ffffffff811c72b5 RDI: 0000000000000001\nRBP: ffff8881067b7db0 R08: 0000000000000000 R09: 205b5d3730353139\nR10: 0000000000000000 R11: 205d303938375420 R12: ffff8881086500c4\nR13: ffff8881086500c4 R14: ffff8881086500b0 R15: ffff888108650040\nFS: 00007f5b2961a4c0(0000) GS:ffff88823bd00000(0000) knlGS:0000000000000000\nCS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\nCR2: 000055d7ed36fd18 CR3: 00000001482f6000 CR4: 00000000000006f0\nDR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000\nDR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400\nCall Trace:\n \n ? show_regs+0xa3/0xc0\n ? __warn+0xa5/0x1c0\n ? refcount_warn_saturate+0xdf/0x1d0\n ? report_bug+0x1fc/0x2d0\n ? refcount_warn_saturate+0xdf/0x1d0\n ? handle_bug+0xa1/0x110\n ? exc_invalid_op+0x3c/0xb0\n ? asm_exc_invalid_op+0x1f/0x30\n ? __warn_printk+0xcc/0x140\n ? __warn_printk+0xd5/0x140\n ? refcount_warn_saturate+0xdf/0x1d0\n get_net_ns+0xa4/0xc0\n ? __pfx_get_net_ns+0x10/0x10\n open_related_ns+0x5a/0x130\n __tun_chr_ioctl+0x1616/0x2370\n ? __sanitizer_cov_trace_switch+0x58/0xa0\n ? __sanitizer_cov_trace_const_cmp2+0x1c/0x30\n ? __pfx_tun_chr_ioctl+0x10/0x10\n tun_chr_ioctl+0x2f/0x40\n __x64_sys_ioctl+0x11b/0x160\n x64_sys_call+0x1211/0x20d0\n do_syscall_64+0x9e/0x1d0\n entry_SYSCALL_64_after_hwframe+0x77/0x7f\nRIP: 0033:0x7f5b28f165d7\nCode: b3 66 90 48 8b 05 b1 48 2d 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 81 48 2d 00 8\nRSP: 002b:00007ffc2b59c5e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010\nRAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f5b28f165d7\nRDX: 0000000000000000 RSI: 00000000000054e3 RDI: 0000000000000003\nRBP: 00007ffc2b59c650 R08: 00007f5b291ed8c0 R09: 00007f5b2961a4c0\nR10: 0000000029690010 R11: 0000000000000246 R12: 0000000000400730\nR13: 00007ffc2b59cf40 R14: 0000000000000000 R15: 0000000000000000\n \nKernel panic - not syncing: kernel: panic_on_warn set ...\n\nThis is trigger as below:\n ns0 ns1\ntun_set_iff() //dev is tun0\n tun->dev = dev\n//ip link set tun0 netns ns1\n put_net() //ref is 0\n__tun_chr_ioctl() //TUNGETDEVNETNS\n net = dev_net(tun->dev);\n open_related_ns(&net->ns, get_net_ns); //ns1\n get_net_ns()\n get_net() //addition on 0\n\nUse maybe_get_net() in get_net_ns in case net's ref is zero to fix this", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.1.21-1+rpt1", "1:6.1.47-1+rpt2", "1:6.1.47-1+rpt4", "1:6.1.54-1+rpt2", "1:6.1.58-1+rpt2", "1:6.1.63-1+rpt1", "1:6.1.73-1+rpt1", "1:6.6.20-1+rpt1", "1:6.6.28-1+rpt1", "1:6.6.31-1+rpt1" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.1.0-rpi1-rpi-v6", "binary_version": "1:6.1.21-1+rpt1" }, { "binary_name": 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"source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-08-05T11:52:36Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 7.8, "cvss_v3_severity": "High", "scenario": "AV:L - The vulnerability is reached through the TUNGETDEVNETNS ioctl on a local /dev/net/tun file descriptor, requiring local system access via the syscall interface. No network or physical vector exists.\nAC:L - The attacker controls both sides of the race \u2014 they create and destroy the target netns themselves and then issue the ioctl, with the zero-refcount window spanning the entire cleanup_net() teardown (synchronize_rcu_expedited plus rcu_barrier), and the attempt is freely repeatable.\nPR:L - An unprivileged user needs only to open /dev/net/tun (mode 0666 on mainstream distros) and hold CAP_NET_ADMIN over namespaces they created, which unshare -Urn grants to any ordinary user; no real root in the initial namespace is required.\nUI:N - The entire sequence \u2014 create tun device, move it to a second netns, destroy that netns, issue the ioctl \u2014 is performed by the attacker's own process with no victim action.\nS:U - The vulnerable code and the impacted resources are both kernel memory under the same security authority; this is conventional local kernel privilege escalation with no VM, IOMMU, or hypervisor boundary crossed.\nC:H - The installed nsfs fd retains a dangling struct net pointer after cleanup_net() frees it via net_free(), and setns() then reads net->user_ns and installs the freed namespace, so all subsequent network syscalls read attacker-groomed freed slab memory, yielding an arbitrary kernel read primitive.\nI:H - put_net() on the freed object performs refcount writes into reclaimed slab memory and can push a freed/live netns onto the global cleanup_list, enabling premature destruction of an in-use namespace and heap corruption exploitable for control-flow hijacking.\nA:H - The immediate effect is a refcount_warn_saturate WARNING that panics the kernel on panic_on_warn systems, and the resulting use-after-free on struct net reliably causes oopses and kernel-wide network state corruption." } } }