Findings

CVE-2025-68199

In the Linux kernel, the following vulnerability has been resolved: codetag: debug: handle existing CODETAG_EMPTY in mark_objexts_empty for slabobj_ext When alloc_slab…

Published Dec 16, 2025 · updated Oct 14, 2026

In the Linux kernel, the following vulnerability has been resolved: codetag: debug: handle existing CODETAG_EMPTY in mark_objexts_empty for slabobj_ext When alloc_slab_obj_exts() fails and then later succeeds in allocating a slab extension vector, it calls handle_failed_objexts_alloc() to mark all objects in the vector as empty. As a result all objects in this slab (slabA) will have their extensions set to CODETAG_EMPTY. Later on if this slabA is used to allocate a slabobj_ext vector for another slab (slabB), we end up with the slabB->obj_exts pointing to a slabobj_ext vector that itself has a non-NULL slabobj_ext equal to CODETAG_EMPTY. When slabB gets freed, free_slab_obj_exts() is called to free slabB->obj_exts vector. free_slab_obj_exts() calls mark_objexts_empty(slabB->obj_exts) which will generate a warning because it expects slabobj_ext vectors to have a NULL obj_ext, not CODETAG_EMPTY. Modify mark_objexts_empty() to skip the warning and setting the obj_ext value if it's already set to CODETAG_EMPTY. To quickly detect this WARN, I modified the code from WARN_ON(slab_exts[offs].ref.ct) to BUG_ON(slab_exts[offs].ref.ct == 1); We then obtained this message: [21630.898561] ------------[ cut here ]------------ [21630.898596] kernel BUG at mm/slub.c:2050! [21630.898611] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP [21630.900372] Modules linked in: squashfs isofs vfio_iommu_type1 vhost_vsock vfio vhost_net vmw_vsock_virtio_transport_common vhost tap vhost_iotlb iommufd vsock binfmt_misc nfsv3 nfs_acl nfs lockd grace netfs tls rds dns_resolver tun brd overlay ntfs3 exfat btrfs blake2b_generic xor xor_neon raid6_pq loop sctp ip6_udp_tunnel udp_tunnel nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables rfkill ip_set sunrpc vfat fat joydev sg sch_fq_codel nfnetlink virtio_gpu sr_mod cdrom drm_client_lib virtio_dma_buf drm_shmem_he