{
  "affected": [
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:12",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.1.170-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:13",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.12.85-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:14",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.19.10-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "details": "In the Linux kernel, the following vulnerability has been resolved:  ceph: fix i_nlink underrun during async unlink  During async unlink, we drop the `i_nlink` counter before we receive the completion (that will eventually update the `i_nlink`) because \"we assume that the unlink will succeed\".  That is not a bad idea, but it races against deletions by other clients (or against the completion of our own unlink) and can lead to an underrun which emits a WARNING like this one:   WARNING: CPU: 85 PID: 25093 at fs/inode.c:407 drop_nlink+0x50/0x68  Modules linked in:  CPU: 85 UID: 3221252029 PID: 25093 Comm: php-cgi8.1 Not tainted 6.14.11-cm4all1-ampere #655  Hardware name: Supermicro ARS-110M-NR/R12SPD-A, BIOS 1.1b 10/17/2023  pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)  pc : drop_nlink+0x50/0x68  lr : ceph_unlink+0x6c4/0x720  sp : ffff80012173bc90  x29: ffff80012173bc90 x28: ffff086d0a45aaf8 x27: ffff0871d0eb5680  x26: ffff087f2a64a718 x25: 0000020000000180 x24: 0000000061c88647  x23: 0000000000000002 x22: ffff07ff9236d800 x21: 0000000000001203  x20: ffff07ff9237b000 x19: ffff088b8296afc0 x18: 00000000f3c93365  x17: 0000000000070000 x16: ffff08faffcbdfe8 x15: ffff08faffcbdfec  x14: 0000000000000000 x13: 45445f65645f3037 x12: 34385f6369706f74  x11: 0000a2653104bb20 x10: ffffd85f26d73290 x9 : ffffd85f25664f94  x8 : 00000000000000c0 x7 : 0000000000000000 x6 : 0000000000000002  x5 : 0000000000000081 x4 : 0000000000000481 x3 : 0000000000000000  x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff08727d3f91e8  Call trace:   drop_nlink+0x50/0x68 (P)   vfs_unlink+0xb0/0x2e8   do_unlinkat+0x204/0x288   __arm64_sys_unlinkat+0x3c/0x80   invoke_syscall.constprop.0+0x54/0xe8   do_el0_svc+0xa4/0xc8   el0_svc+0x18/0x58   el0t_64_sync_handler+0x104/0x130   el0t_64_sync+0x154/0x158  In ceph_unlink(), a call to ceph_mdsc_submit_request() submits the CEPH_MDS_OP_UNLINK to the MDS, but does not wait for completion.  Meanwhile, between this call and the following drop_nlink() call, a worker thread may process a CEPH_CAP_OP_IMPORT, CEPH_CAP_OP_GRANT or just a CEPH_MSG_CLIENT_REPLY (the latter of which could be our own completion).  These will lead to a set_nlink() call, updating the `i_nlink` counter to the value received from the MDS.  If that new `i_nlink` value happens to be zero, it is illegal to decrement it further.  But that is exactly what ceph_unlink() will do then.  The WARNING can be reproduced this way:  1. Force async unlink; only the async code path is affected.  Having    no real clue about Ceph internals, I was unable to find out why the    MDS wouldn't give me the \"Fxr\" capabilities, so I patched    get_caps_for_async_unlink() to always succeed.     (Note that the WARNING dump above was found on an unpatched kernel,    without this kludge - this is not a theoretical bug.)  2. Add a sleep call after ceph_mdsc_submit_request() so the unlink    completion gets handled by a worker thread before drop_nlink() is    called.  This guarantees that the `i_nlink` is already zero before    drop_nlink() runs.  The solution is to skip the counter decrement when it is already zero, but doing so without a lock is still racy (TOCTOU).  Since ceph_fill_inode() and handle_cap_grant() both hold the `ceph_inode_info.i_ceph_lock` spinlock while set_nlink() runs, this seems like the proper lock to protect the `i_nlink` updates.  I found prior art in NFS and SMB (using `inode.i_lock`) and AFS (using `afs_vnode.cb_lock`).  All three have the zero check as well.",
  "id": "DEBIAN-CVE-2026-43420",
  "modified": "2026-09-14T16:47:49.415920315Z",
  "published": "2026-05-08T15:16:54.023Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://security-tracker.debian.org/tracker/CVE-2026-43420"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "upstream": [
    "CVE-2026-43420"
  ]
}