GHSA-VV6W-X7VV-RV35

Vulnerability from github – Published: 2025-12-08 03:31 – Updated: 2025-12-08 03:31
VLAI?
Details

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

fbcon: Set fb_display[i]->mode to NULL when the mode is released

Recently, we discovered the following issue through syzkaller:

BUG: KASAN: slab-use-after-free in fb_mode_is_equal+0x285/0x2f0 Read of size 4 at addr ff11000001b3c69c by task syz.xxx ... Call Trace: dump_stack_lvl+0xab/0xe0 print_address_description.constprop.0+0x2c/0x390 print_report+0xb9/0x280 kasan_report+0xb8/0xf0 fb_mode_is_equal+0x285/0x2f0 fbcon_mode_deleted+0x129/0x180 fb_set_var+0xe7f/0x11d0 do_fb_ioctl+0x6a0/0x750 fb_ioctl+0xe0/0x140 __x64_sys_ioctl+0x193/0x210 do_syscall_64+0x5f/0x9c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Based on experimentation and analysis, during framebuffer unregistration, only the memory of fb_info->modelist is freed, without setting the corresponding fb_display[i]->mode to NULL for the freed modes. This leads to UAF issues during subsequent accesses. Here's an example of reproduction steps: 1. With /dev/fb0 already registered in the system, load a kernel module to register a new device /dev/fb1; 2. Set fb1's mode to the global fb_display[] array (via FBIOPUT_CON2FBMAP); 3. Switch console from fb to VGA (to allow normal rmmod of the ko); 4. Unload the kernel module, at this point fb1's modelist is freed, leaving a wild pointer in fb_display[]; 5. Trigger the bug via system calls through fb0 attempting to delete a mode from fb0.

Add a check in do_unregister_framebuffer(): if the mode to be freed exists in fb_display[], set the corresponding mode pointer to NULL.

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{
  "affected": [],
  "aliases": [
    "CVE-2025-40323"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2025-12-08T01:16:05Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nfbcon: Set fb_display[i]-\u003emode to NULL when the mode is released\n\nRecently, we discovered the following issue through syzkaller:\n\nBUG: KASAN: slab-use-after-free in fb_mode_is_equal+0x285/0x2f0\nRead of size 4 at addr ff11000001b3c69c by task syz.xxx\n...\nCall Trace:\n \u003cTASK\u003e\n dump_stack_lvl+0xab/0xe0\n print_address_description.constprop.0+0x2c/0x390\n print_report+0xb9/0x280\n kasan_report+0xb8/0xf0\n fb_mode_is_equal+0x285/0x2f0\n fbcon_mode_deleted+0x129/0x180\n fb_set_var+0xe7f/0x11d0\n do_fb_ioctl+0x6a0/0x750\n fb_ioctl+0xe0/0x140\n __x64_sys_ioctl+0x193/0x210\n do_syscall_64+0x5f/0x9c0\n entry_SYSCALL_64_after_hwframe+0x76/0x7e\n\nBased on experimentation and analysis, during framebuffer unregistration,\nonly the memory of fb_info-\u003emodelist is freed, without setting the\ncorresponding fb_display[i]-\u003emode to NULL for the freed modes. This leads\nto UAF issues during subsequent accesses. Here\u0027s an example of reproduction\nsteps:\n1. With /dev/fb0 already registered in the system, load a kernel module\n   to register a new device /dev/fb1;\n2. Set fb1\u0027s mode to the global fb_display[] array (via FBIOPUT_CON2FBMAP);\n3. Switch console from fb to VGA (to allow normal rmmod of the ko);\n4. Unload the kernel module, at this point fb1\u0027s modelist is freed, leaving\n   a wild pointer in fb_display[];\n5. Trigger the bug via system calls through fb0 attempting to delete a mode\n   from fb0.\n\nAdd a check in do_unregister_framebuffer(): if the mode to be freed exists\nin fb_display[], set the corresponding mode pointer to NULL.",
  "id": "GHSA-vv6w-x7vv-rv35",
  "modified": "2025-12-08T03:31:01Z",
  "published": "2025-12-08T03:31:01Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-40323"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/468f78276a37f4c6499385a4ce28f4f57be6655d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/4ac18f0e6a6d599ca751c4cd98e522afc8e3d4eb"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a1f3058930745d2b938b6b4f5bd9630dc74b26b7"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/c079d42f70109512eee49123a843be91d8fa133f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/de89d19f4f30d9a8de87b9d08c1bd35cb70576d8"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}


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