# CVE-2023-52894: linux: In the Linux kernel, the following vulnerability has been resolved:  usb: gadget: f_ncm: fix potential NULL ptr deref...

CVE-2023-52894 is fixed in linux on 1 platform, first by DEBIAN-CVE-2023-52894, released August 21, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2023-52894
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0024
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 21, 2024

## Description

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...

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.1.8-1 | [DEBIAN-CVE-2023-52894](https://patchblox.com/security/data/fix/linux/debian-cve-2023-52894.md) | Aug 21, 2024 |
| Linux | linux Debian 13.5 (trixie) | 6.1.8-1 | [DEBIAN-CVE-2023-52894](https://patchblox.com/security/data/fix/linux/debian-cve-2023-52894.md) | Aug 21, 2024 |
| Linux | linux Debian 14 | 6.1.8-1 | [DEBIAN-CVE-2023-52894](https://patchblox.com/security/data/fix/linux/debian-cve-2023-52894.md) | Aug 21, 2024 |

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