ghsa-9r79-4jhv-2rfr
Vulnerability from github
Published
2024-08-21 09:31
Modified
2024-09-11 18:31
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:

usb: gadget: f_ncm: fix potential NULL ptr deref in ncm_bitrate()

In Google internal bug 265639009 we've received an (as yet) unreproducible crash report from an aarch64 GKI 5.10.149-android13 running device.

AFAICT the source code is at: https://android.googlesource.com/kernel/common/+/refs/tags/ASB-2022-12-05_13-5.10

The call stack is: ncm_close() -> ncm_notify() -> ncm_do_notify() with the crash at: ncm_do_notify+0x98/0x270 Code: 79000d0b b9000a6c f940012a f9400269 (b9405d4b)

Which I believe disassembles to (I don't know ARM assembly, but it looks sane enough to me...):

// halfword (16-bit) store presumably to event->wLength (at offset 6 of struct usb_cdc_notification) 0B 0D 00 79 strh w11, [x8, #6]

// word (32-bit) store presumably to req->Length (at offset 8 of struct usb_request) 6C 0A 00 B9 str w12, [x19, #8]

// x10 (NULL) was read here from offset 0 of valid pointer x9 // IMHO we're reading 'cdev->gadget' and getting NULL // gadget is indeed at offset 0 of struct usb_composite_dev 2A 01 40 F9 ldr x10, [x9]

// loading req->buf pointer, which is at offset 0 of struct usb_request 69 02 40 F9 ldr x9, [x19]

// x10 is null, crash, appears to be attempt to read cdev->gadget->max_speed 4B 5D 40 B9 ldr w11, [x10, #0x5c]

which seems to line up with ncm_do_notify() case NCM_NOTIFY_SPEED code fragment:

event->wLength = cpu_to_le16(8); req->length = NCM_STATUS_BYTECOUNT;

/ SPEED_CHANGE data is up/down speeds in bits/sec / data = req->buf + sizeof *event; data[0] = cpu_to_le32(ncm_bitrate(cdev->gadget));

My analysis of registers and NULL ptr deref crash offset (Unable to handle kernel NULL pointer dereference at virtual address 000000000000005c) heavily suggests that the crash is due to 'cdev->gadget' being NULL when executing: data[0] = cpu_to_le32(ncm_bitrate(cdev->gadget)); which calls: ncm_bitrate(NULL) which then calls: gadget_is_superspeed(NULL) which reads ((struct usb_gadget *)NULL)->max_speed and hits a panic.

AFAICT, if I'm counting right, the offset of max_speed is indeed 0x5C. (remember there's a GKI KABI reservation of 16 bytes in struct work_struct)

It's not at all clear to me how this is all supposed to work... but returning 0 seems much better than panic-ing...

Show details on source website

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{
   affected: [],
   aliases: [
      "CVE-2023-52894",
   ],
   database_specific: {
      cwe_ids: [
         "CWE-476",
      ],
      github_reviewed: false,
      github_reviewed_at: null,
      nvd_published_at: "2024-08-21T07:15:05Z",
      severity: "MODERATE",
   },
   details: "In the Linux kernel, the following vulnerability has been resolved:\n\nusb: gadget: f_ncm: fix potential NULL ptr deref in ncm_bitrate()\n\nIn Google internal bug 265639009 we've received an (as yet) unreproducible\ncrash report from an aarch64 GKI 5.10.149-android13 running device.\n\nAFAICT the source code is at:\n  https://android.googlesource.com/kernel/common/+/refs/tags/ASB-2022-12-05_13-5.10\n\nThe call stack is:\n  ncm_close() -> ncm_notify() -> ncm_do_notify()\nwith the crash at:\n  ncm_do_notify+0x98/0x270\nCode: 79000d0b b9000a6c f940012a f9400269 (b9405d4b)\n\nWhich I believe disassembles to (I don't know ARM assembly, but it looks sane enough to me...):\n\n  // halfword (16-bit) store presumably to event->wLength (at offset 6 of struct usb_cdc_notification)\n  0B 0D 00 79    strh w11, [x8, #6]\n\n  // word (32-bit) store presumably to req->Length (at offset 8 of struct usb_request)\n  6C 0A 00 B9    str  w12, [x19, #8]\n\n  // x10 (NULL) was read here from offset 0 of valid pointer x9\n  // IMHO we're reading 'cdev->gadget' and getting NULL\n  // gadget is indeed at offset 0 of struct usb_composite_dev\n  2A 01 40 F9    ldr  x10, [x9]\n\n  // loading req->buf pointer, which is at offset 0 of struct usb_request\n  69 02 40 F9    ldr  x9, [x19]\n\n  // x10 is null, crash, appears to be attempt to read cdev->gadget->max_speed\n  4B 5D 40 B9    ldr  w11, [x10, #0x5c]\n\nwhich seems to line up with ncm_do_notify() case NCM_NOTIFY_SPEED code fragment:\n\n  event->wLength = cpu_to_le16(8);\n  req->length = NCM_STATUS_BYTECOUNT;\n\n  /* SPEED_CHANGE data is up/down speeds in bits/sec */\n  data = req->buf + sizeof *event;\n  data[0] = cpu_to_le32(ncm_bitrate(cdev->gadget));\n\nMy analysis of registers and NULL ptr deref crash offset\n  (Unable to handle kernel NULL pointer dereference at virtual address 000000000000005c)\nheavily suggests that the crash is due to 'cdev->gadget' being NULL when executing:\n  data[0] = cpu_to_le32(ncm_bitrate(cdev->gadget));\nwhich calls:\n  ncm_bitrate(NULL)\nwhich then calls:\n  gadget_is_superspeed(NULL)\nwhich reads\n  ((struct usb_gadget *)NULL)->max_speed\nand hits a panic.\n\nAFAICT, if I'm counting right, the offset of max_speed is indeed 0x5C.\n(remember there's a GKI KABI reservation of 16 bytes in struct work_struct)\n\nIt's not at all clear to me how this is all supposed to work...\nbut returning 0 seems much better than panic-ing...",
   id: "GHSA-9r79-4jhv-2rfr",
   modified: "2024-09-11T18:31:02Z",
   published: "2024-08-21T09:31:32Z",
   references: [
      {
         type: "ADVISORY",
         url: "https://nvd.nist.gov/vuln/detail/CVE-2023-52894",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/09e4507ec8ef2d44da6ba4092b8ee2d81f216497",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/63d161f29cd39c050e8873aa36e0c9fc013bb763",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/a21da7f7aae618c785f7e4a275d43c06dc8412b6",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/a69c8dfb85b44be9cc223be07d35cc3a9baefbea",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/c6ec929595c7443250b2a4faea988c62019d5cd2",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/e92c70059178da751e5af7de02384b7dfadb5ec7",
      },
      {
         type: "WEB",
         url: "https://git.kernel.org/stable/c/fef6b29671b66dfb71f17e337c1ad14b5a2cedae",
      },
   ],
   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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