Red Hat Linux Security Advisories & CVEs
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Latest Red Hat advisories
Medium [CVE-2026-74361] fix FDP fdpcidx bounds check
In the Linux kernel, the following vulnerability has been resolved: nvme: fix FDP fdpcidx bounds check The fdpcidx bounds check sets n = NUMFDPC + 1 but used > instead of >=, incorrectly accepting fdp_idx when it equals n (i.e. A flaw was found in the NVMe (Non-Volatile Memory Express) subsystem of the Linux kernel. An incorrect bounds check in the Flexible Data Placement (FDP) `fdpcidx` function allows an out-of-bounds access. This occurs because the check incorrectly accepts an index value that is beyond the intended boundary. This vulnerability could potentially lead to system instability or other unspecified impacts. Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-125. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 9. Red Hat does not currently list a fixing RHSA for this CVE. Affected products named by the advisory: Red Hat package: kernel-rt.
Medium [CVE-2026-74326] fix resource leak in probe error path
In the Linux kernel, the following vulnerability has been resolved: wifi: mt76: mt7921: fix resource leak in probe error path When pcim_iomap_region() or devm_kmemdup() fail, the code returns directly without cleaning up previously allocated resources: - mt76_device allocated by mt76_alloc_device() - pci irq vectors allocated by pci_alloc_irq_vectors() Fix this by jumping to the existing error cleanup path instead of returning directly. A flaw was found in the Linux kernel's mt76 wireless driver. This flaw occurs when certain memory allocation or I/O mapping functions fail during the probe error path, leading to a failure to deallocate previously reserved resources. This can result in a resource leak, potentially leading to system instability or a denial of service (DoS) condition. Red Hat severity: Low — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-772. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 9. Red Hat does not currently list a fixing RHSA for this CVE. Affected products named by the advisory: Red Hat package: kernel-rt.
Medium [CVE-2026-74308] fix kernel BUG in ext4_write_inline_data_end
In the Linux kernel, the following vulnerability has been resolved: ext4: fix kernel BUG in ext4_write_inline_data_end When the data=journal mount option is used, the ext4_journalled_write_end() function incorrectly calls ext4_write_inline_data_end() without checking if the EXT4_STATE_MAY_INLINE_DATA flag is still set on the inode. If a previous attempt to convert the inline data to an extent failed (e.g. due to ENOSPC), the EXT4_STATE_MAY_INLINE_DATA flag is cleared, but the EXT4_INODE_INLINE_DATA flag remains set. In this scenario, the next call to ext4_write_begin() will not prepare the inline data xattr for writing, but ext4_journalled_write_end() will incorrectly attempt to write to it, triggering a BUG_ON(pos + len > EXT4_I(inode)->i_inline_size) in ext4_write_inline_data() since i_inline_size was not expanded. Fix this by ensuring that ext4_journalled_write_end() only calls ext4_write_inline_data_end() if the EXT4_STATE_MAY_INLINE_DATA flag is set, mirroring the behavior of ext4_write_end() and ext4_da_write_end(). This occurs if a prior attempt to convert inline data to an extent failed, leading to an inconsistent state. An attacker with local access could exploit this to trigger a kernel bug, resulting in a system crash and a Denial of Service (DoS). Red Hat severity: Low — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-805.
Medium [CVE-2026-74344] Clear rb node linkage when freeing bpf_rb_root
In the Linux kernel, the following vulnerability has been resolved: bpf: Clear rb node linkage when freeing bpf_rb_root bpf_rb_root_free() detaches the root by copying the current rb_root_cached and then replacing the live root with RB_ROOT_CACHED. It then walks the copied root and drops each object contained in the tree. This leaves the rb node state intact while dropping the object. If the object is refcounted and survives the drop, its bpf_rb_node_kern still contains an owner pointer to the freed root and stale rb tree linkage. If a later bpf_rb_root allocation reuses the same address, bpf_rbtree_remove() can incorrectly pass the owner check and call rb_erase_cached() on a node whose rb pointers belong to the old tree. This makes surviving nodes unowned and safe to reject from remove or accept for a later add. A flaw was found in the BPF (Berkeley Packet Filter) subsystem of the Linux kernel. When freeing a BPF red-black tree root, the system could leave behind stale pointers in certain objects. If the memory address is reused, a subsequent operation could incorrectly access these stale pointers, leading to memory corruption. This issue could potentially cause system instability or a denial of service. Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-825.
Medium [CVE-2026-74363] fix UAF by restoring RCU-delayed inode freeing in bpffs
In the Linux kernel, the following vulnerability has been resolved: bpf: fix UAF by restoring RCU-delayed inode freeing in bpffs commit 4f375ade6aa9 ("bpf: Avoid RCU context warning when unpinning htab with internal structs") moved inode cleanup from ->free_inode() into ->destroy_inode() to avoid sleeping in RCU context when calling bpf_any_put(). However this removed the RCU delay on freeing the inode itself and the cached symlink body (i_link), both of which can be accessed by RCU pathwalk (pick_link, may_lookup etc.). This causes a use-after-free when a concurrent unlinkat() drops the last inode reference and destroy_inode() frees the inode immediately, while another task is still walking the path in RCU mode and reads inode->i_opflags (offset +2) inside current_time() -> is_mgtime(). Affected products named by the advisory: Red Hat Enterprise Linux 10; Red Hat package: kernel.
Medium [CVE-2026-74349] reject FITRIM ranges shorter than a cluster
In the Linux kernel, the following vulnerability has been resolved: ocfs2: reject FITRIM ranges shorter than a cluster ocfs2_trim_mainbm() trims the global bitmap in cluster units, but its too-short range validation only checks sb->s_blocksize. On filesystems with a cluster size larger than the block size, a FITRIM range that is at least one block but shorter than one cluster is accepted and shifted down to len == 0. The later start + len - 1 and len -=... arithmetic then underflows and can drive trimming past the requested range. That preserves the existing -EINVAL behavior for requests that cannot discard even one allocation unit and keeps zero-cluster trims out of the group walk. A flaw was found in the Linux kernel's OCFS2 (Oracle Cluster File System version 2) component. A local attacker with appropriate permissions could trigger an issue during filesystem trimming operations. By providing a specific range for trimming that is smaller than expected, an internal calculation error (integer underflow) occurs. This error could cause the system to trim data outside the intended area, potentially leading to data corruption or making the system unavailable (Denial of Service). Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-787.
Medium [CVE-2026-74329] unregister PM notifier on watchdog unregister
In the Linux kernel, the following vulnerability has been resolved: watchdog: unregister PM notifier on watchdog unregister watchdog_register_device() registers wdd->pm_nb when WDOG_NO_PING_ON_SUSPEND is set, but watchdog_unregister_device() does not remove it. This leaves an embedded notifier block on the PM notifier chain after the watchdog device has been unregistered. A later suspend/resume notification can then call watchdog_pm_notifier() with a stale watchdog_device pointer, or at minimum after wdd->wd_data has been cleared by watchdog_dev_unregister(). Unregister the PM notifier before tearing down the watchdog device. When a watchdog device is unregistered, its Power Management (PM) notifier may not be properly removed. This can lead to a stale pointer being used during a subsequent suspend/resume operation, potentially causing system instability or a denial of service. Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-825. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 9. Will not fix / out of support: Red Hat Enterprise Linux 6. Red Hat does not currently list a fixing RHSA for this CVE. Affected products named by the advisory: Red Hat package: kernel-rt.
Medium [CVE-2026-74286] allocate per-cpu tstats for PFCP netdevs
In the Linux kernel, the following vulnerability has been resolved: net: pfcp: allocate per-cpu tstats for PFCP netdevs PFCP uses dev_get_tstats64() as its ndo_get_stats64 callback, but pfcp_link_setup() does not request NETDEV_PCPU_STAT_TSTATS. The net core therefore leaves dev->tstats NULL for PFCP devices. Creating a PFCP rtnetlink device can immediately ask the new netdev for stats while building the RTM_NEWLINK notification. That reaches dev_get_tstats64() and dereferences the NULL dev->tstats pointer. Set pcpu_stat_type to NETDEV_PCPU_STAT_TSTATS during PFCP link setup so the net core allocates the storage expected by dev_get_tstats64(). A flaw was found in the Linux kernel's Packet Forwarding Control Protocol (PFCP) module. The module fails to properly allocate per-CPU statistics, leaving a pointer uninitialized. A local attacker can exploit this by creating a PFCP rtnetlink device, which triggers a null pointer dereference. This can lead to a system crash, resulting in a denial of service. Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-476. Red Hat lists Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9 as not affected.
Medium [CVE-2026-74489] fix tid_tx use-after-free on BA session stop
In the Linux kernel, the following vulnerability has been resolved: wifi: mac80211: fix tid_tx use-after-free on BA session stop ieee80211_stop_tx_ba_cb() hands tid_tx to kfree_rcu() through ieee80211_remove_tid_tx(), and then reads tid_tx->ndp after dropping sta->lock: ieee80211_remove_tid_tx(sta, tid);/* kfree_rcu(tid_tx, rcu_head) */... spin_unlock_bh(&sta->lock); if (start_txq) ieee80211_agg_start_txq(sta, tid, false); if (send_delba) ieee80211_send_delba(..., tid_tx->ndp); That read is not covered by an RCU read-side critical section, and it runs in preemptible process context: both callers hold the wiphy mutex, reaching it either from the ieee80211_ba_session_work() wiphy work or from ieee80211_sta_tear_down_BA_sessions() during station teardown. Softirqs can run in that window too, both from the local_bh_enable() that ends ieee80211_agg_start_txq() and from any interrupt exit, so the RCU callback can free tid_tx before the read. Affected products named by the advisory: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 9; Red Hat package: kernel-rt.
Medium [CVE-2026-74527] Block VFs from clobbering special CGX PKIND state
In the Linux kernel, the following vulnerability has been resolved: octeontx2-af: Block VFs from clobbering special CGX PKIND state PF and VF NIX LFs that share a CGX LMAC reuse the same hardware PKIND programming. When HiGig2 or EDSA parsing is enabled, a VF NIX LF alloc must not reset the LMAC RX PKIND or default TX parse config over the PF setup. Add cgx_get_pkind() and rvu_cgx_is_pkind_config_permitted() so VFs skip cgx_set_pkind(), rvu_npc_set_pkind(), and NIX_AF_LFX_TX_PARSE_CFG updates when the LMAC is using NPC_RX_HIGIG_PKIND or NPC_RX_EDSA_PKIND. When Physical Functions (PFs) and Virtual Functions (VFs) share a network interface controller's (NIC) hardware programming (PKIND state), a Virtual Function could overwrite the configuration set by the Physical Function. This could lead to unintended changes in network traffic processing, potentially causing a denial of service or unexpected behavior. Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-1220. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 9. Red Hat does not currently list a fixing RHSA for this CVE. Affected products named by the advisory: Red Hat package: kernel-rt.
Medium [CVE-2026-74558] reclaim invalid Tx descriptors in ZC batch path
In the Linux kernel, the following vulnerability has been resolved: xsk: reclaim invalid Tx descriptors in ZC batch path The zero-copy Tx batch parser stops when it encounters an invalid descriptor. If this happens after one or more continuation descriptors, the Tx consumer can be advanced past fragments that are neither submitted to the driver nor returned to userspace through the completion ring. A similar problem occurs when a packet exceeds xdp_zc_max_segs. The descriptors consumed up to the limit are released without completion, and the remaining continuation descriptors can subsequently be interpreted as the beginning of another packet. Parse Tx batches in packet units and distinguish descriptors belonging to complete valid packets from descriptors consumed while draining an invalid or oversized packet. Return the former to the driver and append the latter to the CQ address area so userspace can reclaim their UMEM frames. Treat a standalone invalid descriptor as a one-descriptor reclaim-only packet. Advancing the Tx-ring consumer releases the ring slot, but does not by itself return ownership of the referenced UMEM frame to userspace. Once draining starts, continue until the packet's end-of-packet descriptor is consumed. Preserve the drain state on the socket when EOP has not yet been supplied, so draining can continue during a later call.
Medium [CVE-2026-74438] sun4i-ss - Remove insecure and unused rng_alg
In the Linux kernel, the following vulnerability has been resolved: crypto: sun4i-ss - Remove insecure and unused rng_alg Remove sun4i_ss_rng, as it is insecure and unused: - It has multiple vulnerabilities. sun4i_ss_prng_seed() is missing locking and has a buffer overflow. sun4i_ss_prng_generate() fails to fill the entire buffer with cryptographic random bytes, because it rounds the destination length down and also doesn't actually wait for the hardware to be ready before pulling bytes from it. - No user of this code is known. It's usable only theoretically via the "rng" algorithm type of AF_ALG. But userspace actually just uses the actual Linux RNG (/dev/random etc) instead. And rng_algs don't contribute entropy to the actual Linux RNG either. (This may have been confused with hwrng, which does contribute entropy.) The sun4i_ss_prng_seed() buffer overflow was reported by Tianchu Chen and discovered by Atuin - Automated Vulnerability Discovery Engine There's no point in fixing all these vulnerabilities individually when this is unused code, so let's just remove it. This component contains multiple vulnerabilities, including a buffer overflow in the sun4i_ss_prng_seed() function that could lead to a denial of service.
Medium [CVE-2026-74531] hold conn reference in abort_conn_sync
In the Linux kernel, the following vulnerability has been resolved: Bluetooth: hci_conn: hold conn reference in abort_conn_sync() There is theoretical UAF if the conn is freed while the hci_sync task is running. Hold refcount to avoid that. A theoretical Use-After-Free (UAF) vulnerability exists if a connection (`conn`) is prematurely freed while the `hci_sync` task is still active. This could potentially allow an attacker to cause a system crash or execute arbitrary code. Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-825. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 9. Will not fix / out of support: Red Hat Enterprise Linux 6. Red Hat does not currently list a fixing RHSA for this CVE. Affected products named by the advisory: Red Hat package: kernel-rt.
Medium [CVE-2026-74550] do not send ICMP/NDISC Redirects when peer allocation fails
In the Linux kernel, the following vulnerability has been resolved: net: do not send ICMP/NDISC Redirects when peer allocation fails When inet_getpeer_v4() or inet_getpeer_v6() fails to allocate a peer entry under memory pressure or tree size caps, redirect handlers previously fell back to sending un-rate-limited ICMP/NDISC Redirect messages. In IPv4, ip_rt_send_redirect() called icmp_send() directly when peer == NULL. In IPv6, ip6_forward() and ndisc_send_redirect() passed a NULL peer into inet_peer_xrlim_allow(), which returned true when peer == NULL. Because ICMP/NDISC Redirects are not part of the default global rate limit mask (sysctl_icmp_ratemask), sending redirects when peer == NULL creates an un-rate-limited ICMP packet storm. Fix this by failing closed in ip_rt_send_redirect(), ip6_forward(), and ndisc_send_redirect() when peer is NULL. When the network stack fails to allocate a peer entry, it can send un-rate-limited Internet Control Message Protocol (ICMP) or Neighbor Discovery (NDISC) Redirect messages. This can be exploited by a remote attacker to cause an uncontrolled flood of network traffic, leading to a Denial of Service (DoS) condition. Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-476.
Medium [CVE-2026-74504] Fix division by zero in initialize_timer
In the Linux kernel, the following vulnerability has been resolved: ALSA: seq: Fix division by zero in initialize_timer() A userspace-driven ALSA timer (SND_UTIMER) lets an unprivileged user set the backing snd_timer's hardware resolution to an arbitrary 64-bit value via SNDRV_TIMER_IOCTL_CREATE. snd_utimer_create() only rejects zero. When such a timer is bound to a sequencer queue, initialize_timer() computes the tick period as tmr->ticks = 1000000000 / (r * freq); where r is that user-controlled resolution and freq is the sequencer update rate in Hz, clamped to MIN_FREQUENCY..MAX_FREQUENCY (10..6250). A resolution of 2^63 makes the 64-bit product r * freq wrap to zero for any even freq, including DEFAULT_FREQUENCY (1000), so the division faults with a divide-by-zero. The division runs under tmr->lock with interrupts disabled, so the oops leaves the spinlock held and hangs the CPU. It is reachable by an unprivileged user with access to /dev/snd/timer and /dev/snd/seq. Oops: divide error: 0000 [#1] SMP KASAN PTI CPU: 7 UID: 1000 PID: 456 Comm: alsa_seq_utimer Not tainted 7.2.0-rc4+ RIP: 0010:initialize_timer.constprop.0+0x20a/0x2d0 snd_seq_timer_start+0x15e/0x2b0 snd_seq_control_queue+0x56f/0xba0 snd_seq_write+0x3e0/0x730 Reject an overflowing product with check_mul_overflow() and fall back to a single tick, which also avoids feeding a wrapped-but-nonzero divisor (e.g.
Medium [CVE-2026-74530] hold conn in hci_connect_big_sync callback
In the Linux kernel, the following vulnerability has been resolved: Bluetooth: hci_sync: hold conn in hci_connect_big_sync() callback There is theoretical UAF if the conn is freed while the hci_sync task is running. Hold refcount to avoid that. Handle NULL hcon, return 0 + do nothing to match the previous behavior. This vulnerability, a Use-After-Free (UAF), occurs when a connection is prematurely released while a related synchronization task in `hci_connect_big_sync()` is still running. This theoretical flaw could allow an attacker to cause a system crash (denial of service) or potentially execute arbitrary code. Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-364. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 9. Red Hat does not currently list a fixing RHSA for this CVE. Affected products named by the advisory: Red Hat package: kernel-rt.
Medium [CVE-2026-74467] Check CAP_NET_ADMIN for private ioctls
In the Linux kernel, the following vulnerability has been resolved: s390/qeth: Check CAP_NET_ADMIN for private ioctls Gate the SIOCDEVPRIVATE ioctl commands SIOC_QETH_ADP_SET_SNMP_CONTROL, SIOC_QETH_GET_CARD_TYPE and SIOC_QETH_QUERY_OAT with CAP_NET_ADMIN capable check to ensure unprivileged users cannot invoke them. An unprivileged local user could exploit this vulnerability by invoking specific SIOCDEVPRIVATE ioctl commands, such as SIOC_QETH_ADP_SET_SNMP_CONTROL, SIOC_QETH_GET_CARD_TYPE, and SIOC_QETH_QUERY_OAT. These commands were not properly restricted by the CAP_NET_ADMIN capability check, allowing unauthorized access to network administration functions. This could lead to a privilege escalation, enabling the unprivileged user to perform actions reserved for privileged accounts. Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-648. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 9. Red Hat does not currently list a fixing RHSA for this CVE. Affected products named by the advisory: Red Hat package: kernel-rt.
Medium [CVE-2026-74546] (adt7470) Fix divide-by-zero TOCTOU crash in fan speed read
In the Linux kernel, the following vulnerability has been resolved: hwmon: (adt7470) Fix divide-by-zero TOCTOU crash in fan speed read If the fan data becomes 0 between the FAN_DATA_VALID() check and the FAN_PERIOD_TO_RPM() conversion, it will result in a divide-by-zero crash due to a race with a concurrent update of the cached fan value. A flaw was found in the Linux kernel's hwmon (hardware monitoring) subsystem, specifically within the adt7470 driver. A local attacker could exploit a time-of-check to time-of-use (TOCTOU) race condition. If fan data becomes zero between a validation check and a conversion operation, it can lead to a divide-by-zero error, causing a system crash and resulting in a Denial of Service (DoS). Red Hat severity: Low — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-369. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6. Will not fix / out of support: Red Hat Enterprise Linux 6. Red Hat does not currently list a fixing RHSA for this CVE. Affected products named by the advisory: Red Hat package: kernel.
Medium [CVE-2026-74507] validate numbered report payloads
In the Linux kernel, the following vulnerability has been resolved: Bluetooth: HIDP: validate numbered report payloads When hidp_get_raw_report() waits for a numbered report, hidp_process_data() compares the expected report number with skb->data[0]. A connected HIDP peer can reply with only a DATA transaction header, leaving the skb empty after the header is removed. KMSAN reports an uninitialized-value use in hidp_session_run(), with the value originating in __alloc_skb() through vhci_write(). The transaction header checks remove the empty-frame reports, but this report remains until the payload check is added. The comparison can also consume a peer-controlled byte beyond the declared L2CAP PDU. A DATA | FEATURE response followed by an extra 0x01 byte made the current code accept that byte as report ID 1 and complete HIDIOCGFEATURE with a zero-byte result. With this change the malformed response is rejected with -EIO, while a subsequent valid response still succeeds. Require a payload byte before comparing a numbered report ID. Unnumbered reports continue to accept an empty payload. A flaw was found in the Linux kernel's Bluetooth Human Interface Device Protocol (HIDP) component. This vulnerability could potentially result in a denial of service or information disclosure. Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H).
Medium [CVE-2026-74484] don't let an 'F' entry pin its own instance
In the Linux kernel, the following vulnerability has been resolved: binfmt_misc: don't let an 'F' entry pin its own instance An entry registered with 'F' opens its interpreter at registration time and holds that file until the entry is freed. Any entry nobody removes by hand only gets closed once the binfmt_misc superblock is shut down. If the interpreter lives on a mount that keeps that superblock alive the two pin each other: binfmt_misc sb -> inode -> entry -> interp_file -> vfsmount -> binfmt_misc sb TL;DR the file is never closed. Once the mount namespace is gone there is nothing left to unregister through either. There are two ways to trigger this bug: - Point the interpreter at the instance itself. Its files are regular files owned by the mounter and both bm_get_inode() and simple_fill_super() leave i_op at empty_iops. So notify_change() falls back to simple_setattr() and chmod +x works. We never set SB_I_NOEXEC and so open_exec() accepts it. - Use the instance as an overlayfs lower layer. The overlay superblock holds a clone_private_mount() of every layer until it is destroyed and that clone is in no namespace. So umount_tree() never reaches it. That's a DoS. And it isn't only the superblock that leaks. It pins the user namespace it was mounted in, so every iteration permanently eats one of the caller's user namespace charges. So let's just do the sane thing.