Filtered by vendor Linux Subscriptions
Total 22492 CVE
CVE Vendors Products Updated CVSS v3.1
CVE-2026-72368 1 Linux 1 Linux Kernel 2026-08-17 7.8 High
In the Linux kernel, the following vulnerability has been resolved: cachefiles: Fix double unlock in nomem_d_alloc error path When start_creating() fails and returns -ENOMEM, it has already released the parent directory lock in __start_dirop(): static struct dentry *__start_dirop(...) { ... inode_lock_nested(dir, I_MUTEX_PARENT); dentry = lookup_one_qstr_excl(name, parent, lookup_flags); if (IS_ERR(dentry)) inode_unlock(dir); <-- Lock released on error return dentry; } However, the nomem_d_alloc error path in cachefiles_get_directory() unconditionally calls inode_unlock(d_inode(dir)) again, causing a double unlock that corrupts the rwsem state. This is a leftover from commit 7ab96df840e60 which replaced manual locking with start_creating() but failed to update the nomem_d_alloc path (while correctly updating mkdir_error and lookup_error paths).
CVE-2026-72371 1 Linux 1 Linux Kernel 2026-08-17 7.8 High
In the Linux kernel, the following vulnerability has been resolved: afs: Fix the volume AFS_VOLUME_RM_TREE is set on Fix afs_insert_volume_into_cell() to set AFS_VOLUME_RM_TREE on the volume replaced, not the new volume, as it's now removed from the cell's volume tree. This will cause the old volume to be removed from the tree twice and the new volume never to be removed.
CVE-2026-72375 1 Linux 1 Linux Kernel 2026-08-17 7.8 High
In the Linux kernel, the following vulnerability has been resolved: afs: Fix reinitialisation of the inode, in particular ->lock_work It seems that initalising afs_vnode::lock_work a single time in the slab's init function isn't sufficient for work_structs. This results in the DEBUG_OBJECTS debugging stuff producing a warning occasionally when running the generic/131 xfstest: ODEBUG: activate not available (active state 0) object: 0000000016d8760f object type: work_struct hint: afs_lock_work+0x0/0x220 WARNING: lib/debugobjects.c:629 at debug_print_object+0x4b/0x90, CPU#3: locktest/7695 ... CPU: 3 UID: 0 PID: 7695 Comm: locktest Tainted: G S 7.1.0-build3+ #2771 PREEMPT ... RIP: 0010:debug_print_object+0x65/0x90 ... Call Trace: <TASK> ? __pfx_afs_lock_work+0x10/0x10 debug_object_activate+0x122/0x170 insert_work+0x25/0x60 __queue_work+0x2e0/0x340 queue_delayed_work_on+0x48/0x70 afs_fl_release_private+0x57/0x70 locks_release_private+0x5c/0xa0 locks_free_lock+0xe/0x20 posix_lock_inode+0x55f/0x5b0 locks_lock_inode_wait+0x81/0x140 ? file_write_and_wait_range+0x50/0x70 afs_lock+0xcd/0x110 fcntl_setlk+0x10d/0x260 do_fcntl+0x24e/0x5b0 __do_sys_fcntl+0x6a/0x90 do_syscall_64+0x11e/0x310 entry_SYSCALL_64_after_hwframe+0x71/0x79 Fix this by reinitialising ->lock_work after allocating an inode. Also, flush ->lock_work when the inode is being evicted to make sure it's not still running.
CVE-2026-72390 1 Linux 1 Linux Kernel 2026-08-17 7.8 High
In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_teql: Introduce slaves_lock to avoid race condition and UAF The teql master->slaves singly linked list is not protected against multiple writes. It can be mod'ed concurently from teql_master_xmit(), teql_dequeue(), teql_init() and teql_destroy() without holding any list lock or RCU protection. zdi-disclosures@trendmicro.com has demonstrated that the qdisc is freed after an RCU grace period, but teql_master_xmit() running on another CPU can still hold a stale pointer into the list, resulting in a slab-use-after-free: BUG: KASAN: slab-use-after-free in teql_master_xmit+0xf0f/0x16b0 Read of size 8 at addr ffff888013fb0440 by task poc/332 Freed 512-byte region [ffff888013fb0400, ffff888013fb0600) (kmalloc-512) The fix? Add a per-master slaves_lock spinlock that serializes all mutations of master->slaves and the NEXT_SLAVE() links in teql_destroy() and teql_qdisc_init(). teql_master_xmit() also takes the same slaves_lock around those updates. Annotate master->slaves and the per-slave ->next pointer with __rcu and use the appropriate RCU accessors everywhere they are touched: rcu_assign_pointer() on the writer side (under slaves_lock), rcu_dereference_protected() for the writer-side loads (also under slaves_lock), rcu_dereference_bh() for the loads in teql_master_xmit() and rtnl_dereference() for the loads in teql_master_open()/teql_master_mtu(), which run under RTNL. Pair this with rcu_read_lock_bh()/rcu_read_unlock_bh() around the list traversal in teql_master_xmit(), so that readers either observe a fully linked list or are deferred until the in-flight mutation completes. The two early-return paths in teql_master_xmit() are updated to release the RCU-bh read-side critical section before returning, since leaving it held would disable BH on that CPU for good.
CVE-2026-72417 1 Linux 1 Linux Kernel 2026-08-17 9.8 Critical
In the Linux kernel, the following vulnerability has been resolved: netfilter: flowtable: Validate iph->ihl in nf_flow_ip4_tunnel_proto() Add sanity check for iph->ihl field in nf_flow_ip4_tunnel_proto() before using it to compute the header size, avoiding out-of-bounds access with malformed IP headers. While at it, use iph->protocol instead of the hardcoded IPPROTO_IPIP constant when setting ctx->tun.proto and reference ctx->tun.hdr_size when updating ctx->offset.
CVE-2026-12702 3 Linux, Microsoft, Octopus 3 Linux Kernel, Windows, Octopus Server 2026-08-17 4.9 Medium
In affected versions of Octopus Deploy Insufficient checks on the project trigger actions allows an unauthorized user to trigger a deployment.
CVE-2026-72250 1 Linux 1 Linux Kernel 2026-08-17 7.8 High
In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_reasm: guard mac_header adjustment after IPv6 defrag nf_ct_frag6_reasm() slides the packet head forward to drop the IPv6 fragment header and then unconditionally advances skb->mac_header: skb->mac_header += sizeof(struct frag_hdr); On the NF_INET_LOCAL_OUT defrag path the skb has no link-layer header yet, so skb->mac_header is still the "not set" sentinel (u16)~0U. Adding sizeof(struct frag_hdr) wraps it to a small value (0xffff + 8 == 7), after which skb_mac_header_was_set() wrongly reports a MAC header is present and skb_mac_header() points into the headroom. The reassembler has done this unconditional add since it was introduced; it was harmless while mac_header was a bare pointer, but wrong once mac_header became a u16 offset whose unset state is the ~0U sentinel tested by skb_mac_header_was_set(). The sibling net/ipv6/reassembly.c does the same relocation and does guard the adjustment; mirror the guard here.
CVE-2026-72252 1 Linux 1 Linux Kernel 2026-08-17 7.8 High
In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_set_pipapo: don't leak bad clone into future transaction On memory allocation failure the cloned nft_pipapo_match can enter a bad state: - some fields can have their lookup tables resized while others did not - bits might have been toggled - scratch map can be undersized which also means m->bsize_max can be lower than what is required This means that the next insertion in the same batch can trigger out-of-bounds writes. Furthermore, a failure in the first can result in the bad clone to leak into the next transaction because the abort callback is never executed in this case (the upper layer saw an error and no attempt to allocate a transactional request was made). Record a state for the nft_pipapo_match structure: - NEW (pristine clone) - MOD (modified clone with good state) - ERR (potentially bogus content) Then make it so that deletes and insertions fail when the clone entered ERR state. In case the very first insert attempt results in an error, free the clone right away.
CVE-2026-72277 1 Linux 1 Linux Kernel 2026-08-17 9.3 Critical
In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: nv: Inject SEA if guest VNCR isn't normal memory When constructing an L1 VNCR mapping, KVM unconditionally uses cacheable memory attributes, even if the underlying PFN isn't memory. This gets particularly hairy if the endpoint doesn't support cacheable memory attributes, potentially throwing an SError on writeback... While KVM does permit cacheable memory attributes on certain PFNMAP VMAs, kvm_translate_vncr() isn't currently grabbing the VMA. So do the simpler thing for now and just reject everything that isn't memory.
CVE-2026-72279 1 Linux 1 Linux Kernel 2026-08-17 9 Critical
In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: nv: Respect read-only PFN when mapping L1 VNCR KVM currently maps the L1 VNCR into the host stage-1 by relying entirely on the permissions of the guest stage-1. At the same time, it is entirely possible that the backing PFN is read-only (e.g. RO memslot), meaning that the L1 VNCR should use at most a read-only mapping. Cache the writability of the PFN in the VNCR TLB and use it to constrain the resulting fixmap permissions. Promote VNCR permission faults to an SEA in the case where the guest attempts to write to a read-only endpoint. Conveniently, this also plugs a page leak found by Sashiko [*] resulting from the early return for a read-only PFN.
CVE-2026-72284 1 Linux 1 Linux Kernel 2026-08-17 7.1 High
In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Ignore pending PV EOI if the vCPU has since disabled PV EOIs Ignore KVM's internal "service pending PV EOI" request if the vCPU has disabled PV EOIs since the request was made. Asserting that PV EOIs are enabled can fail if reading guest memory in pv_eoi_get_user() fails, i.e. if pv_eoi_test_and_clr_pending() bails early, *and* the vCPU also disables PV EOIs. kernel BUG at arch/x86/kvm/lapic.c:3338! Oops: invalid opcode: 0000 [#1] SMP CPU: 4 UID: 1000 PID: 890 Comm: pv_eoi_test Not tainted 7.0.0-d585aa5894d8-vm #337 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:kvm_lapic_sync_from_vapic+0x12b/0x140 [kvm] Call Trace: <TASK> kvm_arch_vcpu_ioctl_run+0x1075/0x1c30 [kvm] kvm_vcpu_ioctl+0x2d5/0x980 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0xb5/0xb40 entry_SYSCALL_64_after_hwframe+0x4b/0x53 </TASK> Modules linked in: kvm_intel kvm irqbypass ---[ end trace 0000000000000000 ]---
CVE-2026-72299 1 Linux 1 Linux Kernel 2026-08-17 9.8 Critical
In the Linux kernel, the following vulnerability has been resolved: tipc: restrict socket queue dumps in enqueue tracepoints tipc_sk_enqueue() runs with sk->sk_lock.slock held while the socket is owned by user context. The spinlock protects the backlog queue in this path, but it does not serialize against the socket owner consuming or purging sk_receive_queue. KASAN reported: CPU: 14 UID: 0 PID: 1050 Comm: tipc3 Not tainted 7.1.0-rc6+ #126 PREEMPT(lazy) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x76/0xa0 lib/dump_stack.c:123 print_report+0xce/0x5b0 mm/kasan/report.c:482 kasan_report+0xc6/0x100 mm/kasan/report.c:597 __asan_report_load4_noabort+0x14/0x30 mm/kasan/report_generic.c:380 tipc_skb_dump+0x1327/0x16f0 net/tipc/trace.c:73 tipc_list_dump+0x208/0x2e0 net/tipc/trace.c:187 tipc_sk_dump+0xaf6/0xd60 net/tipc/socket.c:3996 trace_event_raw_event_tipc_sk_class+0x312/0x5a0 net/tipc/trace.h:188 tipc_sk_rcv+0xb1d/0x1d50 net/tipc/socket.c:2497 tipc_node_xmit+0x1c3/0x1440 net/tipc/node.c:1689 __tipc_sendmsg+0x97a/0x1440 net/tipc/socket.c:1512 tipc_sendmsg+0x52/0x80 net/tipc/socket.c:1400 sock_sendmsg+0x2f6/0x3e0 net/socket.c:825 splice_to_socket+0x7f9/0x1010 fs/splice.c:884 do_splice+0xe21/0x2330 fs/splice.c:936 __do_splice+0x153/0x260 fs/splice.c:1431 __x64_sys_splice+0x150/0x230 fs/splice.c:1616 x64_sys_call+0xeb5/0x2790 arch/x86/entry/syscall_64.c:41 do_syscall_64+0xf3/0x620 arch/x86/entry/syscall_64.c:63 entry_SYSCALL_64_after_hwframe+0x76/0x7e arch/x86/entry/entry_64.S:130 RIP: 0033:0x71624e8aafe2 Code: 08 0f 85 71 3a ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 66 2e 0f 1f 84 00 00 00 00 00 66 RSP: 002b:0000716157ffed68 EFLAGS: 00000246 ORIG_RAX: 0000000000000113 RAX: ffffffffffffffda RBX: 0000716157fff6c0 RCX: 000071624e8aafe2 RDX: 000000000000005f RSI: 0000000000000000 RDI: 0000000000000066 RBP: 0000716157ffed90 R08: 0000000000008000 R09: 0000000000000001 R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffff00 R13: 0000000000000021 R14: 0000000000000000 R15: 00007fff89799c40 </TASK> The TIPC_DUMP_ALL tracepoints in tipc_sk_enqueue() also dump sk_receive_queue and can therefore dereference skbs that the socket owner has already dequeued or freed. Restrict these dumps to TIPC_DUMP_SK_BKLGQ, which matches the queue protected by the held spinlock. Keep the change limited to the enqueue path, where the unsafe queue dump is reachable while the socket is owned by user context.
CVE-2026-72320 1 Linux 1 Linux Kernel 2026-08-17 9.1 Critical
In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_lookup: fix catchall element handling with inverted lookups nft_lookup_eval() decides whether a lookup matched (`found`) from the direct set lookup and priv->invert before falling back to the catchall element used by interval sets (e.g. nft_set_rbtree) for the open-ended default range. Since `found` is never recomputed after `ext` is replaced by the catchall lookup, inverted lookups (NFT_LOOKUP_F_INV, "!= @set") can wrongly match or wrongly skip the catchall element, producing the wrong verdict. Fold the catchall lookup into `ext` before computing `found`, matching the order already used by nft_objref_map_eval().
CVE-2026-72339 1 Linux 1 Linux Kernel 2026-08-17 9.8 Critical
In the Linux kernel, the following vulnerability has been resolved: qede: fix off-by-one in BD ring consumption on build_skb failure qede_rx_build_skb() and qede_tpa_rx_build_skb() do not check for a NULL return from qede_build_skb(). When it returns NULL under memory pressure, the functions still consume a BD from the ring before returning NULL. The callers then recycle additional BDs, resulting in one extra BD being consumed (off-by-one). This desynchronizes the BD ring, which can corrupt DMA page reference counts and lead to SLUB freelist corruption. Commit 4e910dbe3650 ("qede: confirm skb is allocated before using") added a NULL check inside qede_build_skb() to prevent a NULL pointer dereference, but did not address the missing NULL checks in the callers, making this off-by-one reachable. Fix this by adding NULL checks for the return value of qede_build_skb() in both qede_rx_build_skb() and qede_tpa_rx_build_skb(), returning NULL immediately before any BD ring manipulation.
CVE-2026-72344 1 Linux 1 Linux Kernel 2026-08-17 7.8 High
In the Linux kernel, the following vulnerability has been resolved: net/mlx5e: TC, skip peer flow cleanup when LAG seq is unavailable mlx5_lag_get_dev_seq() will return error when the peer isn't in the LAG or when no device is marked as master. Result bad memory access and kernel crash[1]. Hence, skip the peer when lookup fails. Note: In case there are peer flows, they are cleaned before LAG cleared the master mark. [1] RIP: 0010:mlx5e_tc_del_fdb_peers_flow+0x3d/0x350 [mlx5_core] Call Trace: <TASK> mlx5e_tc_clean_fdb_peer_flows+0xc1/0x130 [mlx5_core] mlx5_esw_offloads_unpair+0x3a/0x400 [mlx5_core] mlx5_esw_offloads_devcom_event+0xee/0x360 [mlx5_core] mlx5_devcom_send_event+0x7a/0x140 [mlx5_core] mlx5_esw_offloads_devcom_cleanup+0x2f/0x90 [mlx5_core] mlx5e_tc_esw_cleanup+0x28/0xf0 [mlx5_core] mlx5e_rep_tc_cleanup+0x19/0x30 [mlx5_core] mlx5e_cleanup_uplink_rep_tx+0x36/0x40 [mlx5_core] mlx5e_cleanup_rep_tx+0x55/0x60 [mlx5_core] mlx5e_detach_netdev+0x96/0xf0 [mlx5_core] mlx5e_netdev_change_profile+0x5b/0x120 [mlx5_core] mlx5e_netdev_attach_nic_profile+0x1b/0x30 [mlx5_core] mlx5e_vport_rep_unload+0xdd/0x110 [mlx5_core] __esw_offloads_unload_rep+0x81/0xb0 [mlx5_core] mlx5_eswitch_unregister_vport_reps+0x1d7/0x220 [mlx5_core] mlx5e_rep_remove+0x22/0x30 [mlx5_core] device_release_driver_internal+0x194/0x1f0 bus_remove_device+0xe8/0x1b0 device_del+0x159/0x3c0 mlx5_rescan_drivers_locked+0xbc/0x2d0 [mlx5_core] mlx5_unregister_device+0x54/0x80 [mlx5_core] mlx5_uninit_one+0x73/0x130 [mlx5_core] remove_one+0x78/0xe0 [mlx5_core] pci_device_remove+0x39/0xa0
CVE-2026-72347 1 Linux 1 Linux Kernel 2026-08-17 7.3 High
In the Linux kernel, the following vulnerability has been resolved: netfilter: xt_connmark: reject invalid shift parameters Revision 2 of the CONNMARK target accepts user-controlled shift parameters and applies them to 32-bit mark values in connmark_tg_shift(). A shift_bits value of 32 or more triggers an undefined-shift bug when the rule is evaluated. Invalid shift_dir values are also accepted and silently fall back to the left-shift path. Reject invalid revision-2 shift parameters in connmark_tg_check() so malformed rules fail at installation time, before they can reach the packet path.
CVE-2026-72367 1 Linux 1 Linux Kernel 2026-08-17 8.8 High
In the Linux kernel, the following vulnerability has been resolved: iomap: guard io_size EOF trim against concurrent truncate underflow iomap: fix zero padding data issue in concurrent append writes changed ioend accounting so that io_size tracks only valid data within EOF. This trims io_size when a writeback range extends past end_pos: ioend->io_size += map_len; if (ioend->io_offset + ioend->io_size > end_pos) ioend->io_size = end_pos - ioend->io_offset; However, if end_pos ends up below ioend->io_offset, the subtraction becomes negative and is stored in size_t io_size, causing an unsigned wrap to a huge value. This can happen when writeback continues past byte-level EOF up to a block-aligned range, or when a concurrent truncate shrinks the file after end_pos was sampled in iomap_writeback_handle_eof(). A wrapped io_size can mislead append detection and corrupt completion-time size handling, since filesystem end_io paths consume io_size for decisions such as on-disk EOF updates and unwritten/COW completion ranges. Fix this by clamping io_size to zero when EOF has moved to or before the ioend start offset. This preserves the original intent of trimming io_size to valid in-EOF data while avoiding the underflow.
CVE-2026-72409 1 Linux 1 Linux Kernel 2026-08-17 7.5 High
In the Linux kernel, the following vulnerability has been resolved: net: mvneta: re-enable percpu interrupt on resume On Marvell MPIC platforms (Armada 370/XP/38x), mvneta uses a percpu IRQ disable/enable scheme for NAPI: the ISR (mvneta_percpu_isr) calls disable_percpu_irq() to mask the MPIC per-CPU interrupt and schedules NAPI poll, which calls enable_percpu_irq() on completion to unmask. If suspend occurs while NAPI poll is pending (between disable_percpu_irq in the ISR and enable_percpu_irq in poll completion), the interrupt is never re-enabled: 1. mvneta_percpu_isr: disable_percpu_irq() + napi_schedule() => MPIC masked, percpu_enabled cpumask bit cleared 2. NAPI poll does not complete before suspend proceeds (on PREEMPT_RT this is highly likely since softirqs run in ksoftirqd which gets frozen; on non-RT it can happen when softirq processing is deferred to ksoftirqd) 3. mvneta_stop_dev => napi_disable(): cancels the pending poll without executing the completion path 4. suspend_device_irqs => IRQCHIP_MASK_ON_SUSPEND: masks MPIC (already masked, but records IRQS_SUSPENDED) 5. Resume: mpic_resume checks irq_percpu_is_enabled() => false (bit was cleared in step 1) => skips unmask 6. mvneta_start_dev only restores device-level INTR_NEW_MASK, does not touch the MPIC per-CPU mask Result: MPIC per-CPU interrupt stays masked permanently. The NIC generates interrupts (INTR_NEW_CAUSE != 0) but the CPU never receives them, causing complete loss of network connectivity. Fix by calling on_each_cpu(mvneta_percpu_enable) in the resume path to unconditionally unmask the MPIC per-CPU interrupt regardless of pre-suspend state.
CVE-2026-72103 1 Linux 1 Linux Kernel 2026-08-17 7.3 High
In the Linux kernel, the following vulnerability has been resolved: dm: avoid leaking the caller's thread keyring via the table device file The refactoring in commit a28d893eb327 ("md: port block device access to file") accidentally causes the caller's thread keyring to be kept alive long beyond the caller's lifetime. As a result, "cryptsetup luksSuspend" silently fails to wipe the LUKS volume key from memory. In detail: "cryptsetup luksOpen" uses its supposedly ephemeral thread keyring to pass the volume key to the kernel. dm-crypt's crypt_set_keyring_key() copies the key material into its own crypt_config structure and then drops its own reference to the key in the keyring with key_put(). With this fix, restoring pre-v6.9 behavior, the copy in the thread keyring is then promptly garbage collected, such that exactly one copy of the volume key remains. This single copy is correctly wiped from memory on "cryptsetup luksSuspend". Without this fix, the thread keyring and the volume key in it remains. This second copy is only freed on "luksClose". "luksSuspend" neither knows about this copy nor has any way to remove it, so the key remains recoverable from RAM after a suspend that is documented to have wiped it. This fix should not introduce new security problems, as the code is anyway gated by CAP_SYS_ADMIN. The device-mapper core, not the calling task, is the legitimate owner of this long-lived file.
CVE-2026-72170 1 Linux 1 Linux Kernel 2026-08-17 7.8 High
In the Linux kernel, the following vulnerability has been resolved: 9p: skip nlink update in cacheless mode to fix WARN_ON v9fs_dec_count() unconditionally calls drop_nlink() on regular files, even when the inode's nlink is already zero. In cacheless mode the client refetches inode metadata from the server (the source of truth) on every operation, so by the time v9fs_remove() returns, the locally cached nlink may already reflect the post-unlink value: 1. Client initiates unlink, server processes it and sets nlink to 0 2. Client refetches inode metadata (nlink=0) before unlink returns 3. Client's v9fs_remove() completes successfully 4. Client calls v9fs_dec_count() which calls drop_nlink() on nlink=0 This race is easily triggered under heavy unlink workloads, such as stress-ng's unlink stressor, producing the following warning: WARNING: fs/inode.c:417 at drop_nlink+0x4c/0xc8 Call trace: drop_nlink+0x4c/0xc8 v9fs_remove+0x1e0/0x250 [9p] v9fs_vfs_unlink+0x20/0x38 [9p] vfs_unlink+0x13c/0x258 ... In cacheless mode the server is authoritative and the inode is on its way out, so locally adjusting nlink buys nothing. Skip v9fs_dec_count() entirely when neither CACHE_META nor CACHE_LOOSE is set, which both avoids the warning and removes a class of nlink races (two concurrent unlinkers observing nlink > 0 and both calling drop_nlink()) that an nlink == 0 guard alone would only narrow rather than close.