{ "schema_version": "1.6.1", "id": "RPI-CVE-2024-41041", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2024-41041" ], "published": "2024-07-29T14:32:49Z", "summary": "udp: Set SOCK_RCU_FREE earlier in udp_lib_get_port().", "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nudp: Set SOCK_RCU_FREE earlier in udp_lib_get_port().\n\nsyzkaller triggered the warning [0] in udp_v4_early_demux().\n\nIn udp_v[46]_early_demux() and sk_lookup(), we do not touch the refcount\nof the looked-up sk and use sock_pfree() as skb->destructor, so we check\nSOCK_RCU_FREE to ensure that the sk is safe to access during the RCU grace\nperiod.\n\nCurrently, SOCK_RCU_FREE is flagged for a bound socket after being put\ninto the hash table. Moreover, the SOCK_RCU_FREE check is done too early\nin udp_v[46]_early_demux() and sk_lookup(), so there could be a small race\nwindow:\n\n CPU1 CPU2\n ---- ----\n udp_v4_early_demux() udp_lib_get_port()\n | |- hlist_add_head_rcu()\n |- sk = __udp4_lib_demux_lookup() |\n |- DEBUG_NET_WARN_ON_ONCE(sk_is_refcounted(sk));\n `- sock_set_flag(sk, SOCK_RCU_FREE)\n\nWe had the same bug in TCP and fixed it in commit 871019b22d1b (\"net:\nset SOCK_RCU_FREE before inserting socket into hashtable\").\n\nLet's apply the same fix for UDP.\n\n[0]:\nWARNING: CPU: 0 PID: 11198 at net/ipv4/udp.c:2599 udp_v4_early_demux+0x481/0xb70 net/ipv4/udp.c:2599\nModules linked in:\nCPU: 0 PID: 11198 Comm: syz-executor.1 Not tainted 6.9.0-g93bda33046e7 #13\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014\nRIP: 0010:udp_v4_early_demux+0x481/0xb70 net/ipv4/udp.c:2599\nCode: c5 7a 15 fe bb 01 00 00 00 44 89 e9 31 ff d3 e3 81 e3 bf ef ff ff 89 de e8 2c 74 15 fe 85 db 0f 85 02 06 00 00 e8 9f 7a 15 fe <0f> 0b e8 98 7a 15 fe 49 8d 7e 60 e8 4f 39 2f fe 49 c7 46 60 20 52\nRSP: 0018:ffffc9000ce3fa58 EFLAGS: 00010293\nRAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff8318c92c\nRDX: ffff888036ccde00 RSI: ffffffff8318c2f1 RDI: 0000000000000001\nRBP: ffff88805a2dd6e0 R08: 0000000000000001 R09: 0000000000000000\nR10: 0000000000000000 R11: 0001ffffffffffff R12: ffff88805a2dd680\nR13: 0000000000000007 R14: ffff88800923f900 R15: ffff88805456004e\nFS: 00007fc449127640(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000\nCS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\nCR2: 00007fc449126e38 CR3: 000000003de4b002 CR4: 0000000000770ef0\nDR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000\nDR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600\nPKRU: 55555554\nCall Trace:\n \n ip_rcv_finish_core.constprop.0+0xbdd/0xd20 net/ipv4/ip_input.c:349\n ip_rcv_finish+0xda/0x150 net/ipv4/ip_input.c:447\n NF_HOOK include/linux/netfilter.h:314 [inline]\n NF_HOOK include/linux/netfilter.h:308 [inline]\n ip_rcv+0x16c/0x180 net/ipv4/ip_input.c:569\n __netif_receive_skb_one_core+0xb3/0xe0 net/core/dev.c:5624\n __netif_receive_skb+0x21/0xd0 net/core/dev.c:5738\n netif_receive_skb_internal net/core/dev.c:5824 [inline]\n netif_receive_skb+0x271/0x300 net/core/dev.c:5884\n tun_rx_batched drivers/net/tun.c:1549 [inline]\n tun_get_user+0x24db/0x2c50 drivers/net/tun.c:2002\n tun_chr_write_iter+0x107/0x1a0 drivers/net/tun.c:2048\n new_sync_write fs/read_write.c:497 [inline]\n vfs_write+0x76f/0x8d0 fs/read_write.c:590\n ksys_write+0xbf/0x190 fs/read_write.c:643\n __do_sys_write fs/read_write.c:655 [inline]\n __se_sys_write fs/read_write.c:652 [inline]\n __x64_sys_write+0x41/0x50 fs/read_write.c:652\n x64_sys_call+0xe66/0x1990 arch/x86/include/generated/asm/syscalls_64.h:2\n do_syscall_x64 arch/x86/entry/common.c:52 [inline]\n do_syscall_64+0x4b/0x110 arch/x86/entry/common.c:83\n entry_SYSCALL_64_after_hwframe+0x4b/0x53\nRIP: 0033:0x7fc44a68bc1f\nCode: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 e9 cf f5 ff 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 3c d0 f5 ff 48\nRSP: 002b:00007fc449126c90 EFLAGS: 00000293 ORIG_RAX: 0000000000000001\nRAX: ffffffffffffffda RBX: 00000000004bc050 RCX: 00007fc44a68bc1f\nR\n---truncated---", "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": "linux-image-6.1.0-rpi1-rpi-v7", 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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 racing writer side is `udp_lib_get_port()`, reached only through a local `bind()`/`connect()` syscall on a UDP socket, and the reader side needs a packet on a dst-less receive path (tun/veth), which the attacker creates locally in their own netns. A remote peer sending UDP packets cannot by itself put a socket into the unflagged window, so the bug is not remotely reachable.\nAC:L - The attacker owns both halves of the race \u2014 a thread loop calling `bind()`/`connect()` on UDP sockets and a concurrent injector feeding matching packets through tun/veth \u2014 and can widen the window by contending `hslot2->lock` and by running massively in parallel across CPUs. Per the race guidance, an attacker-created race is Low complexity.\nPR:L - Binding UDP sockets requires no privilege at all, and the packet-injection side (tun/veth creation) is obtained by any unprivileged user via `unshare -Urn`, where CAP_NET_ADMIN is granted in the new user namespace. No real root or init-namespace capability is needed.\nUI:N - The attacker performs every step \u2014 socket binding, device setup, and packet injection \u2014 with no action required from any other user or administrator.\nS:U - The refcount underflow, use-after-free, and any resulting panic all occur in the kernel of the same host under the same security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - `skb_steal_sock()` reading a stale-clear `SOCK_RCU_FREE` yields `refcounted == true`, so `udp_rcv()` drops a reference it never took, freeing `struct udp_sock` while the owning fd and the hash tables still point at it. The resulting use-after-free lets an attacker refill the slab and read back kernel memory through subsequent socket operations.\nI:H - The same unbalanced `sock_put()` produces a use-after-free on a socket object containing function pointers (`sk_prot`, `sk_data_ready`, `sk_destruct`) and list heads, which is a classic heap-spray target giving arbitrary-write and control-flow-hijack primitives.\nA:H - The race trips `DEBUG_NET_WARN_ON_ONCE()` in `udp_v4_early_demux()` and the unconditional `WARN_ONCE(1, \"Found non-RCU, unreferenced socket!\")` in `sk_lookup()`, tainting the kernel and panicking outright on `panic_on_warn=1` systems; the premature socket free additionally corrupts the UDP hash lists and crashes the kernel even when not exploited further." } } }