ghsa-2h93-g5hm-9qcv
Vulnerability from github
Published
2024-10-21 18:30
Modified
2024-11-13 15:31
Severity ?
5.5 (Medium) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Details

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

mm, slub: avoid zeroing kmalloc redzone

Since commit 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated kmalloc space than requested"), setting orig_size treats the wasted space (object_size - orig_size) as a redzone. However with init_on_free=1 we clear the full object->size, including the redzone.

Additionally we clear the object metadata, including the stored orig_size, making it zero, which makes check_object() treat the whole object as a redzone.

These issues lead to the following BUG report with "slub_debug=FUZ init_on_free=1":

[ 0.000000] ============================================================================= [ 0.000000] BUG kmalloc-8 (Not tainted): kmalloc Redzone overwritten [ 0.000000] ----------------------------------------------------------------------------- [ 0.000000] [ 0.000000] 0xffff000010032858-0xffff00001003285f @offset=2136. First byte 0x0 instead of 0xcc [ 0.000000] FIX kmalloc-8: Restoring kmalloc Redzone 0xffff000010032858-0xffff00001003285f=0xcc [ 0.000000] Slab 0xfffffdffc0400c80 objects=36 used=23 fp=0xffff000010032a18 flags=0x3fffe0000000200(workingset|node=0|zone=0|lastcpupid=0x1ffff) [ 0.000000] Object 0xffff000010032858 @offset=2136 fp=0xffff0000100328c8 [ 0.000000] [ 0.000000] Redzone ffff000010032850: cc cc cc cc cc cc cc cc ........ [ 0.000000] Object ffff000010032858: cc cc cc cc cc cc cc cc ........ [ 0.000000] Redzone ffff000010032860: cc cc cc cc cc cc cc cc ........ [ 0.000000] Padding ffff0000100328b4: 00 00 00 00 00 00 00 00 00 00 00 00 ............ [ 0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.11.0-rc3-next-20240814-00004-g61844c55c3f4 #144 [ 0.000000] Hardware name: NXP i.MX95 19X19 board (DT) [ 0.000000] Call trace: [ 0.000000] dump_backtrace+0x90/0xe8 [ 0.000000] show_stack+0x18/0x24 [ 0.000000] dump_stack_lvl+0x74/0x8c [ 0.000000] dump_stack+0x18/0x24 [ 0.000000] print_trailer+0x150/0x218 [ 0.000000] check_object+0xe4/0x454 [ 0.000000] free_to_partial_list+0x2f8/0x5ec

To address the issue, use orig_size to clear the used area. And restore the value of orig_size after clear the remaining area.

When CONFIG_SLUB_DEBUG not defined, (get_orig_size()' directly returns s->object_size. So when using memset to init the area, the size can simply be orig_size, as orig_size returns object_size when CONFIG_SLUB_DEBUG not enabled. And orig_size can never be bigger than object_size.

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{
  "affected": [],
  "aliases": [
    "CVE-2024-49885"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2024-10-21T18:15:11Z",
    "severity": "MODERATE"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm, slub: avoid zeroing kmalloc redzone\n\nSince commit 946fa0dbf2d8 (\"mm/slub: extend redzone check to extra\nallocated kmalloc space than requested\"), setting orig_size treats\nthe wasted space (object_size - orig_size) as a redzone. However with\ninit_on_free=1 we clear the full object-\u003esize, including the redzone.\n\nAdditionally we clear the object metadata, including the stored orig_size,\nmaking it zero, which makes check_object() treat the whole object as a\nredzone.\n\nThese issues lead to the following BUG report with \"slub_debug=FUZ\ninit_on_free=1\":\n\n[    0.000000] =============================================================================\n[    0.000000] BUG kmalloc-8 (Not tainted): kmalloc Redzone overwritten\n[    0.000000] -----------------------------------------------------------------------------\n[    0.000000]\n[    0.000000] 0xffff000010032858-0xffff00001003285f @offset=2136. First byte 0x0 instead of 0xcc\n[    0.000000] FIX kmalloc-8: Restoring kmalloc Redzone 0xffff000010032858-0xffff00001003285f=0xcc\n[    0.000000] Slab 0xfffffdffc0400c80 objects=36 used=23 fp=0xffff000010032a18 flags=0x3fffe0000000200(workingset|node=0|zone=0|lastcpupid=0x1ffff)\n[    0.000000] Object 0xffff000010032858 @offset=2136 fp=0xffff0000100328c8\n[    0.000000]\n[    0.000000] Redzone  ffff000010032850: cc cc cc cc cc cc cc cc                          ........\n[    0.000000] Object   ffff000010032858: cc cc cc cc cc cc cc cc                          ........\n[    0.000000] Redzone  ffff000010032860: cc cc cc cc cc cc cc cc                          ........\n[    0.000000] Padding  ffff0000100328b4: 00 00 00 00 00 00 00 00 00 00 00 00              ............\n[    0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.11.0-rc3-next-20240814-00004-g61844c55c3f4 #144\n[    0.000000] Hardware name: NXP i.MX95 19X19 board (DT)\n[    0.000000] Call trace:\n[    0.000000]  dump_backtrace+0x90/0xe8\n[    0.000000]  show_stack+0x18/0x24\n[    0.000000]  dump_stack_lvl+0x74/0x8c\n[    0.000000]  dump_stack+0x18/0x24\n[    0.000000]  print_trailer+0x150/0x218\n[    0.000000]  check_object+0xe4/0x454\n[    0.000000]  free_to_partial_list+0x2f8/0x5ec\n\nTo address the issue, use orig_size to clear the used area. And restore\nthe value of orig_size after clear the remaining area.\n\nWhen CONFIG_SLUB_DEBUG not defined, (get_orig_size()\u0027 directly returns\ns-\u003eobject_size. So when using memset to init the area, the size can simply\nbe orig_size, as orig_size returns object_size when CONFIG_SLUB_DEBUG not\nenabled. And orig_size can never be bigger than object_size.",
  "id": "GHSA-2h93-g5hm-9qcv",
  "modified": "2024-11-13T15:31:36Z",
  "published": "2024-10-21T18:30:56Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-49885"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/59090e479ac78ae18facd4c58eb332562a23020e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/7a2e823a19746d54052c625faecf0d2d6c52ee0a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/83f0440b2f92227fcce9898118ca7fe7e0d64b1f"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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