# CVE-2024-36892: linux: In the Linux kernel, the following vulnerability has been resolved:  mm/slub: avoid zeroing outside-object freepointe...

CVE-2024-36892 is fixed in linux on 1 platform, first by DEBIAN-CVE-2024-36892, released May 30, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2024-36892
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0020
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 30, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  mm/slub: avoid zeroing outside-object freepointer for single free  Commit 284f17ac13fe ("mm/slub: handle bulk and single object freeing separately") splits single and bulk object freeing in two functions slab_free() and slab_free_bulk() which leads slab_free() to call slab_free_hook() directly instead of slab_free_freelist_hook().  If `init_on_free` is set, slab_free_hook() zeroes the object. Afterward, if `slub_debug=F` and `CONFIG_SLAB_FREELIST_HARDENED` are set, the do_slab_free() slowpath executes freelist consistency checks and try to decode a zeroed freepointer which leads to a "Freepointer corrupt" detection in check_object().  During bulk free, slab_free_freelist_hook() isn't affected as it always sets it objects freepointer using set_freepointer() to maintain its reconstructed freelist after `init_on_free`.  For single free, object's freepointer thus needs to be avoided when stored outside the object if `init_on_free` is set. The freepointer left as is, check_object() may later detect an invalid pointer value due to objects overflow.  To reproduce, set `slub_debug=FU init_on_free=1 log_level=7` on the command line of a kernel build with `CONFIG_SLAB_FREELIST_HARDENED=y`.  dmesg sample log: [   10.708715] ============================================================================= [   10.710323] BUG kmalloc-rnd-05-32 (Tainted: G    B           T ): Freepointer corrupt [   10.712695] ----------------------------------------------------------------------------- [   10.712695] [   10.712695] Slab 0xffffd8bdc400d580 objects=32 used=4 fp=0xffff9d9a80356f80 flags=0x200000000000a00(workingset|slab|node=0|zone=2) [   10.716698] Object 0xffff9d9a80356600 @offset=1536 fp=0x7ee4f480ce0ecd7c [   10.716698] [   10.716698] Bytes b4 ffff9d9a803565f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................ [   10.720703] Object   ffff9d9a80356600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................ [   10.720703] Object   ffff9d9a80356610: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................ [   10.724696] Padding  ffff9d9a8035666c: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................ [   10.724696] Padding  ffff9d9a8035667c: 00 00 00 00                                      .... [   10.724696] FIX kmalloc-rnd-05-32: Object at 0xffff9d9a80356600 not freed

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.8.11-1 | [DEBIAN-CVE-2024-36892](https://patchblox.com/security/data/fix/linux/debian-cve-2024-36892.md) | May 30, 2024 |
| Linux | linux Debian 14 | 6.8.11-1 | [DEBIAN-CVE-2024-36892](https://patchblox.com/security/data/fix/linux/debian-cve-2024-36892.md) | May 30, 2024 |

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