{ "schema_version": "1.6.1", "id": "RPI-CVE-2025-21868", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2025-21868" ], "published": "2025-03-27T13:38:45Z", "summary": "net: allow small head cache usage with large MAX_SKB_FRAGS values", "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: allow small head cache usage with large MAX_SKB_FRAGS values\n\nSabrina reported the following splat:\n\n WARNING: CPU: 0 PID: 1 at net/core/dev.c:6935 netif_napi_add_weight_locked+0x8f2/0xba0\n Modules linked in:\n CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.14.0-rc1-net-00092-g011b03359038 #996\n Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014\n RIP: 0010:netif_napi_add_weight_locked+0x8f2/0xba0\n Code: e8 c3 e6 6a fe 48 83 c4 28 5b 5d 41 5c 41 5d 41 5e 41 5f c3 cc cc cc cc c7 44 24 10 ff ff ff ff e9 8f fb ff ff e8 9e e6 6a fe <0f> 0b e9 d3 fe ff ff e8 92 e6 6a fe 48 8b 04 24 be ff ff ff ff 48\n RSP: 0000:ffffc9000001fc60 EFLAGS: 00010293\n RAX: 0000000000000000 RBX: ffff88806ce48128 RCX: 1ffff11001664b9e\n RDX: ffff888008f00040 RSI: ffffffff8317ca42 RDI: ffff88800b325cb6\n RBP: ffff88800b325c40 R08: 0000000000000001 R09: ffffed100167502c\n R10: ffff88800b3a8163 R11: 0000000000000000 R12: ffff88800ac1c168\n R13: ffff88800ac1c168 R14: ffff88800ac1c168 R15: 0000000000000007\n FS: 0000000000000000(0000) GS:ffff88806ce00000(0000) knlGS:0000000000000000\n CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n CR2: ffff888008201000 CR3: 0000000004c94001 CR4: 0000000000370ef0\n DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000\n DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400\n Call Trace:\n \n gro_cells_init+0x1ba/0x270\n xfrm_input_init+0x4b/0x2a0\n xfrm_init+0x38/0x50\n ip_rt_init+0x2d7/0x350\n ip_init+0xf/0x20\n inet_init+0x406/0x590\n do_one_initcall+0x9d/0x2e0\n do_initcalls+0x23b/0x280\n kernel_init_freeable+0x445/0x490\n kernel_init+0x20/0x1d0\n ret_from_fork+0x46/0x80\n ret_from_fork_asm+0x1a/0x30\n \n irq event stamp: 584330\n hardirqs last enabled at (584338): [] __up_console_sem+0x77/0xb0\n hardirqs last disabled at (584345): [] __up_console_sem+0x5c/0xb0\n softirqs last enabled at (583242): [] netlink_insert+0x14d/0x470\n softirqs last disabled at (583754): [] netif_napi_add_weight_locked+0x77d/0xba0\n\non kernel built with MAX_SKB_FRAGS=45, where SKB_WITH_OVERHEAD(1024)\nis smaller than GRO_MAX_HEAD.\n\nSuch built additionally contains the revert of the single page frag cache\nso that napi_get_frags() ends up using the page frag allocator, triggering\nthe splat.\n\nNote that the underlying issue is independent from the mentioned\nrevert; address it ensuring that the small head cache will fit either TCP\nand GRO allocation and updating napi_alloc_skb() and __netdev_alloc_skb()\nto select kmalloc() usage for any allocation fitting such cache.", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.6.20-1+rpt1", "1:6.6.28-1+rpt1", "1:6.6.31-1+rpt1", "1:6.6.47-1+rpt1", "1:6.6.51-1+rpt1", "1:6.6.51-1+rpt2", "1:6.6.51-1+rpt3", "1:6.6.62-1+rpt1", "1:6.6.74-1+rpt1" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.6.20+rpt-rpi-2712", "binary_version": "1:6.6.20-1+rpt1" }, { "binary_name": "linux-image-6.6.20+rpt-rpi-v6", "binary_version": "1:6.6.20-1+rpt1" }, { "binary_name": "linux-image-6.6.20+rpt-rpi-v7", "binary_version": "1:6.6.20-1+rpt1" }, { "binary_name": "linux-image-6.6.20+rpt-rpi-v7l", "binary_version": "1:6.6.20-1+rpt1" }, { "binary_name": "linux-image-6.6.20+rpt-rpi-v8", "binary_version": "1:6.6.20-1+rpt1" }, { "binary_name": "linux-image-6.6.28+rpt-rpi-2712", "binary_version": "1:6.6.28-1+rpt1" }, { "binary_name": "linux-image-6.6.28+rpt-rpi-v6", "binary_version": "1:6.6.28-1+rpt1" }, { 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"linux_commit": "a18d9ced4965462cb7b3b4252ada440395105308", "upstream_version": "6.6.74", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.6.117" } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2025-21868" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/ed8a77fee4618facd2a539cad7b7366697b5a575" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/ed0ca7d2127c63991cfaf1932b827e3f4f8ee480" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/648e440c98e260dec835e48a5d7a9993477b1f9d" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/14ad6ed30a10afbe91b0749d6378285f4225d482" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-08-05T12:19:11Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 7.5, "cvss_v3_severity": "High", "scenario": "AV:N - The defective allocation path is `napi_alloc_skb(napi, GRO_MAX_HEAD)` inside `napi_get_frags()`, driven entirely by inbound packets processed by NAPI/GRO in drivers such as gve, mlx4, ionic, sfc, cxgb4 and tun. A remote peer sending traffic to the host reaches it with no local access.\nAC:L - On an affected build the mis-selection is deterministic \u2014 every GRO head allocation takes the page-frag path, with no race, timing window, or memory-layout dependency \u2014 and the attacker only needs to send small packets and drain the socket slowly to pin pages. Per CVSS 3.1 \u00a73.6 the non-default `CONFIG_MAX_SKB_FRAGS` value is scored as the assumed vulnerable configuration rather than as attack complexity.\nPR:N - The RX/GRO allocation path runs before any socket-level authentication or authorization; unsolicited packets from an unauthenticated remote host are enough to drive it. No credentials on the target are required.\nUI:N - Packet reception and GRO processing happen automatically in softirq context. No victim action of any kind is needed.\nS:U - The over-consumed memory and the failed accounting both belong to the kernel's own networking subsystem; no security authority boundary such as a VM, IOMMU, or sandbox is crossed.\nC:N - The bug only changes which allocator backs `skb->head`; buffers are still correctly sized and bounded, so no out-of-bounds read or kernel memory disclosure occurs.\nI:N - There is no out-of-bounds write, use-after-free, or type confusion \u2014 allocation sizes remain correct and freeing is consistently routed through `skb_free_frag()` for `head_frag` skbs, so no attacker-controlled data modification is possible.\nA:H - Each ~1.1 KB GRO head pins a slice of a 32 KB order-3 page while reporting a truesize ~23x smaller, so `tcp_mem`, `sk_rmem_alloc` and cgroup socket-memory limits are bypassed and sustained remote small-packet traffic drives the host into memory exhaustion and OOM \u2014 the exact production failure documented in the regressed commit 3226b158e67c. On non-4K-page builds the same condition additionally trips the `WARN_ON_ONCE` in `netif_napi_add_weight_locked()`, which is a boot-time panic under `panic_on_warn`." } } }