{ "schema_version": "1.6.1", "id": "RPI-CVE-2026-64108", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2026-64108" ], "published": "2026-07-19T15:41:06Z", "summary": "cifs: Fix busy dentry used after unmounting", "details": "In the Linux kernel, the following vulnerability has been resolved:\n\ncifs: Fix busy dentry used after unmounting\n\nSince commit 340cea84f691c (\"cifs: open files should not hold ref on\nsuperblock\"), cifs file only holds the dentry ref_cnt, the cifs file\nclose work(cfile->deferred) could be executed after unmounting, which\nwill trigger a warning in generic_shutdown_super:\n BUG: Dentry 00000000a14a6845{i=c,n=file} still in use (1) [unmount of\n cifs cifs]\n\nThe detailed processs is:\n process A process B kworker\n fd = open(PATH)\n vfs_open\n file->__f_path = *path // dentry->d_lockref.count = 1\n cifs_open\n cifs_new_fileinfo\n cfile->dentry = dget(dentry) // dentry->d_lockref.count = 2\n close(fd)\n __fput\n cifs_close\n queue_delayed_work(deferredclose_wq, cfile->deferred)\n dput(dentry) // dentry->d_lockref.count = 1\n\t\t\t smb2_deferred_work_close\n\t\t\t\t\t _cifsFileInfo_put\n\t\t\t\t\t list_del(&cifs_file->flist)\n umount\n\t\t cleanup_mnt\n\t\t deactivate_super\n\t\t cifs_kill_sb\n\t\t cifs_close_all_deferred_files_sb\n\t\t\t cifs_close_all_deferred_files\n\t\t\t // cannot find cfile, skip _cifsFileInfo_put\n\t\t\tkill_anon_super\n\t\t\t generic_shutdown_super\n\t\t\t shrink_dcache_for_umount\n\t\t\t umount_check\n\t\t\t WARN ! // dentry->d_lockref.count = 1\n\t\t\t\t\t cifsFileInfo_put_final\n\t\t\t\t\t dput(cifs_file->dentry)\n\t\t // dentry->d_lockref.count = 0\n\nFix it by flushing 'deferredclose_wq' before calling kill_anon_super.\n\nFetch a reproducer in https://bugzilla.kernel.org/show_bug.cgi?id=221548.", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.12.87-1+rpt1~bookworm" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.12.87+rpt-rpi-2712", "binary_version": "1:6.12.87-1+rpt1~bookworm" }, { "binary_name": "linux-image-6.12.87+rpt-rpi-v6", "binary_version": "1:6.12.87-1+rpt1~bookworm" }, { "binary_name": "linux-image-6.12.87+rpt-rpi-v7", "binary_version": "1:6.12.87-1+rpt1~bookworm" }, { "binary_name": "linux-image-6.12.87+rpt-rpi-v7l", "binary_version": "1:6.12.87-1+rpt1~bookworm" }, { "binary_name": "linux-image-6.12.87+rpt-rpi-v8", "binary_version": "1:6.12.87-1+rpt1~bookworm" }, { "binary_name": "linux-image-6.12.87+rpt-rpi-v8-rt", "binary_version": "1:6.12.87-1+rpt1~bookworm" } ] }, "database_specific": { "per_version": { "1:6.12.87-1+rpt1~bookworm": { "linux_commit": "ae4d75fb36deba0fe1a986d9bfae65755e082dd0", "upstream_version": "6.12.87", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.12.92" } } } }, { "package": { "ecosystem": "Raspberry Pi OS:13", "name": "linux" }, "versions": [ "1:6.18.29-1+rpt1", "1:6.18.33-1+rpt1" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.18.29+rpt-rpi-2712", "binary_version": "1:6.18.29-1+rpt1" }, { "binary_name": "linux-image-6.18.29+rpt-rpi-v6", "binary_version": "1:6.18.29-1+rpt1" }, { "binary_name": "linux-image-6.18.29+rpt-rpi-v7", "binary_version": "1:6.18.29-1+rpt1" }, { "binary_name": "linux-image-6.18.29+rpt-rpi-v8", "binary_version": "1:6.18.29-1+rpt1" }, { "binary_name": "linux-image-6.18.29+rpt-rpi-v8-rt", "binary_version": "1:6.18.29-1+rpt1" }, { "binary_name": "linux-image-6.18.33+rpt-rpi-2712", "binary_version": "1:6.18.33-1+rpt1" }, { "binary_name": "linux-image-6.18.33+rpt-rpi-v6", "binary_version": "1:6.18.33-1+rpt1" }, { "binary_name": "linux-image-6.18.33+rpt-rpi-v7", "binary_version": "1:6.18.33-1+rpt1" }, { "binary_name": "linux-image-6.18.33+rpt-rpi-v8", "binary_version": "1:6.18.33-1+rpt1" }, { "binary_name": "linux-image-6.18.33+rpt-rpi-v8-rt", "binary_version": "1:6.18.33-1+rpt1" } ] }, "database_specific": { "per_version": { "1:6.18.29-1+rpt1": { "linux_commit": "66318c5b5cd8145a662303af12ed39ac07eb27cc", "upstream_version": "6.18.29", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.18.34" }, "1:6.18.33-1+rpt1": { "linux_commit": "95b85bebbedcaedfa7ca79116ed38b7376fba412", "upstream_version": "6.18.33", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.18.34" } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2026-64108" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/c7364cea52531534676b9f7dbc0a477c11f4c050" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/bdc349a87f1fb02c18c4071858a06542bfea783d" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/f2deaa2f409a4598eaa10f2a93a676c0632af248" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/5e7d9d0805e58fa3760894e73115b7a74024fd07" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/e1ffa6cf662383f95816eed1b623429d82675e75" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/c68337442f03953237a94577beb468ab2662a851" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-08-05T13:16:28Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 7.8, "cvss_v3_severity": "High", "scenario": "AV:L - The bug is reached through local VFS syscalls (open, close, umount) in the CIFS client mount teardown path, not through remote packet handling or in-kernel SMB server code.\nAC:L - An attacker controls both sides of the race by opening/closing files to queue deferred-close work (default 1-second closetimeo) and concurrently triggering umount, and can retry until the window is hit.\nPR:L - Exploitation requires only an unprivileged local user with access to files on an already-mounted CIFS/SMB3 share; mount/umount can be supplied by the attacker in a separate thread if they hold CAP_SYS_ADMIN, or by autofs/system umount on shared enterprise mounts.\nUI:N - No victim interaction is required; the attacker drives the open/close/umount syscall sequence directly without relying on another user to open files or click anything.\nS:U - Impact is confined to kernel memory corruption and privilege boundaries within the same host; this is not a VM escape, sandbox escape, or cross-security-authority boundary flaw.\nC:H - The deferred-close worker performs use-after-free on dentry, inode, and super_block structures after unmount teardown, which can be leveraged for arbitrary kernel memory read per standard UAF guidance.\nI:H - Post-unmount _cifsFileInfo_put() and cifsFileInfo_put_final() operate on freed kernel objects and can corrupt heap metadata or control flow, enabling arbitrary write or code execution primitives.\nA:H - The race triggers a WARN in generic_shutdown_super during umount and subsequent use-after-free in the deferred-close worker can cause kernel oops, panic, or hang." } } }