ghsa-2v5c-9mj7-vp9g
Vulnerability from github
Published
2025-09-16 15:32
Modified
2025-09-16 15:32
Details

In the Linux kernel, the following vulnerability has been resolved:

atm: atmtcp: Prevent arbitrary write in atmtcp_recv_control().

syzbot reported the splat below. [0]

When atmtcp_v_open() or atmtcp_v_close() is called via connect() or close(), atmtcp_send_control() is called to send an in-kernel special message.

The message has ATMTCP_HDR_MAGIC in atmtcp_control.hdr.length. Also, a pointer of struct atm_vcc is set to atmtcp_control.vcc.

The notable thing is struct atmtcp_control is uAPI but has a space for an in-kernel pointer.

struct atmtcp_control { struct atmtcp_hdr hdr; / must be first / ... atm_kptr_t vcc; / both directions / ... } __ATM_API_ALIGN;

typedef struct { unsigned char _[8]; } __ATM_API_ALIGN atm_kptr_t;

The special message is processed in atmtcp_recv_control() called from atmtcp_c_send().

atmtcp_c_send() is vcc->dev->ops->send() and called from 2 paths:

  1. .ndo_start_xmit() (vcc->send() == atm_send_aal0())
  2. vcc_sendmsg()

The problem is sendmsg() does not validate the message length and userspace can abuse atmtcp_recv_control() to overwrite any kptr by atmtcp_control.

Let's add a new ->pre_send() hook to validate messages from sendmsg().

[0]: Oops: general protection fault, probably for non-canonical address 0xdffffc00200000ab: 0000 [#1] SMP KASAN PTI KASAN: probably user-memory-access in range [0x0000000100000558-0x000000010000055f] CPU: 0 UID: 0 PID: 5865 Comm: syz-executor331 Not tainted 6.17.0-rc1-syzkaller-00215-gbab3ce404553 #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 RIP: 0010:atmtcp_recv_control drivers/atm/atmtcp.c:93 [inline] RIP: 0010:atmtcp_c_send+0x1da/0x950 drivers/atm/atmtcp.c:297 Code: 4d 8d 75 1a 4c 89 f0 48 c1 e8 03 42 0f b6 04 20 84 c0 0f 85 15 06 00 00 41 0f b7 1e 4d 8d b7 60 05 00 00 4c 89 f0 48 c1 e8 03 <42> 0f b6 04 20 84 c0 0f 85 13 06 00 00 66 41 89 1e 4d 8d 75 1c 4c RSP: 0018:ffffc90003f5f810 EFLAGS: 00010203 RAX: 00000000200000ab RBX: 0000000000000000 RCX: 0000000000000000 RDX: ffff88802a510000 RSI: 00000000ffffffff RDI: ffff888030a6068c RBP: ffff88802699fb40 R08: ffff888030a606eb R09: 1ffff1100614c0dd R10: dffffc0000000000 R11: ffffffff8718fc40 R12: dffffc0000000000 R13: ffff888030a60680 R14: 000000010000055f R15: 00000000ffffffff FS: 00007f8d7e9236c0(0000) GS:ffff888125c1c000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000000045ad50 CR3: 0000000075bde000 CR4: 00000000003526f0 Call Trace: vcc_sendmsg+0xa10/0xc60 net/atm/common.c:645 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg+0x219/0x270 net/socket.c:729 _syssendmsg+0x505/0x830 net/socket.c:2614 _sys_sendmsg+0x21f/0x2a0 net/socket.c:2668 __sys_sendmsg net/socket.c:2700 [inline] __do_sys_sendmsg net/socket.c:2705 [inline] __se_sys_sendmsg net/socket.c:2703 [inline] __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f8d7e96a4a9 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f8d7e923198 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f8d7e9f4308 RCX: 00007f8d7e96a4a9 RDX: 0000000000000000 RSI: 0000200000000240 RDI: 0000000000000005 RBP: 00007f8d7e9f4300 R08: 65732f636f72702f R09: 65732f636f72702f R10: 65732f636f72702f R11: 0000000000000246 R12: 00007f8d7e9c10ac R13: 00007f8d7e9231a0 R14: 0000200000000200 R15: 0000200000000250 Modules linked in:

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{
  "affected": [],
  "aliases": [
    "CVE-2025-39828"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2025-09-16T13:16:03Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\natm: atmtcp: Prevent arbitrary write in atmtcp_recv_control().\n\nsyzbot reported the splat below. [0]\n\nWhen atmtcp_v_open() or atmtcp_v_close() is called via connect()\nor close(), atmtcp_send_control() is called to send an in-kernel\nspecial message.\n\nThe message has ATMTCP_HDR_MAGIC in atmtcp_control.hdr.length.\nAlso, a pointer of struct atm_vcc is set to atmtcp_control.vcc.\n\nThe notable thing is struct atmtcp_control is uAPI but has a\nspace for an in-kernel pointer.\n\n  struct atmtcp_control {\n  \tstruct atmtcp_hdr hdr;\t/* must be first */\n  ...\n  \tatm_kptr_t vcc;\t\t/* both directions */\n  ...\n  } __ATM_API_ALIGN;\n\n  typedef struct { unsigned char _[8]; } __ATM_API_ALIGN atm_kptr_t;\n\nThe special message is processed in atmtcp_recv_control() called\nfrom atmtcp_c_send().\n\natmtcp_c_send() is vcc-\u003edev-\u003eops-\u003esend() and called from 2 paths:\n\n  1. .ndo_start_xmit() (vcc-\u003esend() == atm_send_aal0())\n  2. vcc_sendmsg()\n\nThe problem is sendmsg() does not validate the message length and\nuserspace can abuse atmtcp_recv_control() to overwrite any kptr\nby atmtcp_control.\n\nLet\u0027s add a new -\u003epre_send() hook to validate messages from sendmsg().\n\n[0]:\nOops: general protection fault, probably for non-canonical address 0xdffffc00200000ab: 0000 [#1] SMP KASAN PTI\nKASAN: probably user-memory-access in range [0x0000000100000558-0x000000010000055f]\nCPU: 0 UID: 0 PID: 5865 Comm: syz-executor331 Not tainted 6.17.0-rc1-syzkaller-00215-gbab3ce404553 #0 PREEMPT(full)\nHardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025\nRIP: 0010:atmtcp_recv_control drivers/atm/atmtcp.c:93 [inline]\nRIP: 0010:atmtcp_c_send+0x1da/0x950 drivers/atm/atmtcp.c:297\nCode: 4d 8d 75 1a 4c 89 f0 48 c1 e8 03 42 0f b6 04 20 84 c0 0f 85 15 06 00 00 41 0f b7 1e 4d 8d b7 60 05 00 00 4c 89 f0 48 c1 e8 03 \u003c42\u003e 0f b6 04 20 84 c0 0f 85 13 06 00 00 66 41 89 1e 4d 8d 75 1c 4c\nRSP: 0018:ffffc90003f5f810 EFLAGS: 00010203\nRAX: 00000000200000ab RBX: 0000000000000000 RCX: 0000000000000000\nRDX: ffff88802a510000 RSI: 00000000ffffffff RDI: ffff888030a6068c\nRBP: ffff88802699fb40 R08: ffff888030a606eb R09: 1ffff1100614c0dd\nR10: dffffc0000000000 R11: ffffffff8718fc40 R12: dffffc0000000000\nR13: ffff888030a60680 R14: 000000010000055f R15: 00000000ffffffff\nFS:  00007f8d7e9236c0(0000) GS:ffff888125c1c000(0000) knlGS:0000000000000000\nCS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\nCR2: 000000000045ad50 CR3: 0000000075bde000 CR4: 00000000003526f0\nCall Trace:\n \u003cTASK\u003e\n vcc_sendmsg+0xa10/0xc60 net/atm/common.c:645\n sock_sendmsg_nosec net/socket.c:714 [inline]\n __sock_sendmsg+0x219/0x270 net/socket.c:729\n ____sys_sendmsg+0x505/0x830 net/socket.c:2614\n ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668\n __sys_sendmsg net/socket.c:2700 [inline]\n __do_sys_sendmsg net/socket.c:2705 [inline]\n __se_sys_sendmsg net/socket.c:2703 [inline]\n __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703\n do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]\n do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94\n entry_SYSCALL_64_after_hwframe+0x77/0x7f\nRIP: 0033:0x7f8d7e96a4a9\nCode: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 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 \u003c48\u003e 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48\nRSP: 002b:00007f8d7e923198 EFLAGS: 00000246 ORIG_RAX: 000000000000002e\nRAX: ffffffffffffffda RBX: 00007f8d7e9f4308 RCX: 00007f8d7e96a4a9\nRDX: 0000000000000000 RSI: 0000200000000240 RDI: 0000000000000005\nRBP: 00007f8d7e9f4300 R08: 65732f636f72702f R09: 65732f636f72702f\nR10: 65732f636f72702f R11: 0000000000000246 R12: 00007f8d7e9c10ac\nR13: 00007f8d7e9231a0 R14: 0000200000000200 R15: 0000200000000250\n \u003c/TASK\u003e\nModules linked in:",
  "id": "GHSA-2v5c-9mj7-vp9g",
  "modified": "2025-09-16T15:32:36Z",
  "published": "2025-09-16T15:32:35Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-39828"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0a6a6d4fb333f7afe22e59ffed18511a7a98efc8"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/33f9e6dc66b32202b95fc861e6b3ea4b0c185b0b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3ab9f5ad9baefe6d3d4c37053cdfca2761001dfe"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3c80c230d6e3e6f63d43f4c3f0bb344e3e8b119b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/51872b26429077be611b0a1816e0e722278015c3"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/62f368472b0aa4b5d91d9b983152855c6b6d8925"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/b502f16bad8f0a4cfbd023452766f21bfda39dde"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ec79003c5f9d2c7f9576fc69b8dbda80305cbe3a"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}


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