{ "schema_version": "1.6.1", "id": "RPI-CVE-2024-38538", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2024-38538" ], "published": "2024-06-19T13:36:08Z", "summary": "net: bridge: xmit: make sure we have at least eth header len bytes", "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: bridge: xmit: make sure we have at least eth header len bytes\n\nsyzbot triggered an uninit value[1] error in bridge device's xmit path\nby sending a short (less than ETH_HLEN bytes) skb. To fix it check if\nwe can actually pull that amount instead of assuming.\n\nTested with dropwatch:\n drop at: br_dev_xmit+0xb93/0x12d0 [bridge] (0xffffffffc06739b3)\n origin: software\n timestamp: Mon May 13 11:31:53 2024 778214037 nsec\n protocol: 0x88a8\n length: 2\n original length: 2\n drop reason: PKT_TOO_SMALL\n\n[1]\nBUG: KMSAN: uninit-value in br_dev_xmit+0x61d/0x1cb0 net/bridge/br_device.c:65\n br_dev_xmit+0x61d/0x1cb0 net/bridge/br_device.c:65\n __netdev_start_xmit include/linux/netdevice.h:4903 [inline]\n netdev_start_xmit include/linux/netdevice.h:4917 [inline]\n xmit_one net/core/dev.c:3531 [inline]\n dev_hard_start_xmit+0x247/0xa20 net/core/dev.c:3547\n __dev_queue_xmit+0x34db/0x5350 net/core/dev.c:4341\n dev_queue_xmit include/linux/netdevice.h:3091 [inline]\n __bpf_tx_skb net/core/filter.c:2136 [inline]\n __bpf_redirect_common net/core/filter.c:2180 [inline]\n __bpf_redirect+0x14a6/0x1620 net/core/filter.c:2187\n ____bpf_clone_redirect net/core/filter.c:2460 [inline]\n bpf_clone_redirect+0x328/0x470 net/core/filter.c:2432\n ___bpf_prog_run+0x13fe/0xe0f0 kernel/bpf/core.c:1997\n __bpf_prog_run512+0xb5/0xe0 kernel/bpf/core.c:2238\n bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]\n __bpf_prog_run include/linux/filter.h:657 [inline]\n bpf_prog_run include/linux/filter.h:664 [inline]\n bpf_test_run+0x499/0xc30 net/bpf/test_run.c:425\n bpf_prog_test_run_skb+0x14ea/0x1f20 net/bpf/test_run.c:1058\n bpf_prog_test_run+0x6b7/0xad0 kernel/bpf/syscall.c:4269\n __sys_bpf+0x6aa/0xd90 kernel/bpf/syscall.c:5678\n __do_sys_bpf kernel/bpf/syscall.c:5767 [inline]\n __se_sys_bpf kernel/bpf/syscall.c:5765 [inline]\n __x64_sys_bpf+0xa0/0xe0 kernel/bpf/syscall.c:5765\n x64_sys_call+0x96b/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:322\n do_syscall_x64 arch/x86/entry/common.c:52 [inline]\n do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83\n entry_SYSCALL_64_after_hwframe+0x77/0x7f", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/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", "binary_version": "1:6.1.21-1+rpt1" }, { "binary_name": "linux-image-6.1.0-rpi1-rpi-v7l", "binary_version": "1:6.1.21-1+rpt1" }, { "binary_name": "linux-image-6.1.0-rpi1-rpi-v8", "binary_version": "1:6.1.21-1+rpt1" }, { "binary_name": "linux-image-6.1.0-rpi2-rpi-v6", "binary_version": "1:6.1.47-1+rpt2" }, { "binary_name": "linux-image-6.1.0-rpi2-rpi-v7", "binary_version": "1:6.1.47-1+rpt2" }, { "binary_name": "linux-image-6.1.0-rpi2-rpi-v7l", "binary_version": "1:6.1.47-1+rpt2" 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version (no usable Linux commit)", "upstream_fixed": "6.1.93" }, "1:6.6.20-1+rpt1": { "linux_commit": "6f16847710cc0502450788b9f12f0a14d3429668", "upstream_version": "6.6.20", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.6.33" }, "1:6.6.28-1+rpt1": { "linux_commit": "0c341f47adc3578cd5f817aa20ee2b7f9ae6b23e", "upstream_version": "6.6.28", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.6.33" }, "1:6.6.31-1+rpt1": { "linux_commit": "c1432b4bae5b6582f4d32ba381459f33c34d1424", "upstream_version": "6.6.31", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.6.33" } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2024-38538" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/3e01fc3c66e65d9afe98f1489047a1b2dd8741ca" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/b2b7c43cd32080221bb233741bd6011983fe7c11" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/82090f94c723dab724b1c32db406091d40448a17" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/c964429ef53f42098a6545a5dabeb1441c1e821d" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/28126b83f86ab9cc7936029c2dff845d3dcedba2" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/1abb371147905ba250b4cc0230c4be7e90bea4d5" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/f482fd4ce919836a49012b2d31b00fc36e2488f2" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/5b5d669f569807c7ab07546e73c0741845a2547a" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/8bd67ebb50c0145fd2ca8681ab65eb7e8cde1afc" } ], "database_specific": { "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": 7.3, "cvss_v3_severity": "High", "scenario": "AV:L - `br_dev_xmit()` is the bridge device's locally-originated transmit path \u2014 remotely received frames go through `br_handle_frame`/`br_forward` and always carry a full Ethernet header, and IP routing toward a bridge always builds one via `dev_hard_header()`. Triggering it requires local injection of a sub-14-byte skb (tun write or AF_PACKET on a `hard_header_len == 0` device, plus a tc `mirred` redirect).\nAC:L - The attacker fully and deterministically controls the skb length; there is no race, no timing window, and no dependence on memory layout or victim state. Every attempt reaches the uninitialized read and the subsequent `skb_push()` leak.\nPR:L - The setup needs CAP_NET_ADMIN/CAP_NET_RAW only within a network namespace, which any unprivileged user obtains via `unshare -Urn` (create the bridge, create the tun/tunnel device, attach the tc mirred redirect, and capture leaked frames from a veth peer). No real root in the initial namespace is required.\nUI:N - The attacker performs every step \u2014 creating the devices, writing the short frame, and reading the leaked frames back \u2014 with no action by any other user or administrator.\nS:U - The uninitialized read, the malformed skb, and the resulting disclosure all stay within the kernel's own security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - Up to 14 bytes of uninitialized kernel heap (skb headroom and the region past `skb->tail`, which routinely holds freed packet data and kernel values) are read and then, via the unconditional `skb_push(skb, ETH_HLEN)` in `br_dev_queue_push_xmit()`, transmitted verbatim out every bridge port where the attacker captures them. The leak is repeatable at packet rate, yielding an effectively unbounded kernel memory disclosure rather than a bounded few-byte read.\nI:L - There is no out-of-bounds write primitive, but the kernel emits malformed frames whose source/destination MAC addresses are uninitialized memory, and forwarding decisions (broadcast/multicast/unicast, FDB lookup) are made on that garbage \u2014 corrupting local and peer bridge/switch forwarding state in a limited, attacker-influenced way.\nA:H - When the short skb has less than ETH_HLEN of headroom (as in the syzbot BPF-redirect reproducer), `skb_push(skb, ETH_HLEN)` in `br_dev_queue_push_xmit()` drives `skb->data` below `skb->head` and hits `skb_under_panic()` \u2192 `BUG()`, a hard kernel panic. Additionally the resulting skb has `mac_header`/`network_header` desynchronized from `skb->data`, propagating a malformed skb into the generic xmit path (e.g. the `WARN_ONCE` in `skb_checksum_help()`, fatal under `panic_on_warn`), and the trigger can be repeated indefinitely." } } }