Filtered by vendor Linux Subscriptions
Total 22338 CVE
CVE Vendors Products Updated CVSS v3.1
CVE-2026-72431 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: alloc_tag: fix use-after-free in /proc/allocinfo after module unload allocinfo_start() only reinitializes the codetag iterator at position 0. For subsequent reads (position > 0), it reuses cached iterator state from the previous batch. allocinfo_stop() drops mod_lock between read batches, which allows module unload to complete and free the module memory that the cached iterator still references: CPU0 (read) CPU1 (rmmod) ---- ---- allocinfo_start(pos=0) down_read(mod_lock) allocinfo_show() ... allocinfo_stop() up_read(mod_lock) codetag_unload_module() kfree(cmod) release_module_tags() ... free_mod_mem() allocinfo_start(pos=N) down_read(mod_lock) // reuses cached iter, skips re-init allocinfo_show() ct->filename <-- UAF After free_mod_mem() frees the module's .rodata, allocinfo_show() dereferences ct->filename, ct->function which point there. Save the iterator state in allocinfo_next() and resume from it in allocinfo_start() with codetag_next_ct(), which detects module removal via idr_find() returning NULL and skips to the next module.
CVE-2026-72430 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: net/sched: act_ct: fix nf_connlabels leak on two error paths tcf_ct_fill_params() calls nf_connlabels_get() (setting put_labels) when TCA_CT_LABELS is present, but two later error sites use a bare return instead of "goto err", skipping the err: nf_connlabels_put() cleanup. They also precede the "p->put_labels = put_labels" assignment, so the tcf_ct_params_free() fallback does not release the count either. Each failed RTM_NEWACTION on these paths leaks one nf_connlabels reference: net->ct.labels_used is incremented and never released. The action is reachable with CAP_NET_ADMIN over the netns, i.e. from an unprivileged user namespace on default-userns kernels. Impact: an unprivileged user with CAP_NET_ADMIN over a network namespace (e.g. via user namespaces) leaks one nf_connlabels reference per failed RTM_NEWACTION on the two error paths; net->ct.labels_used is never released. The err: label is safe to reach from both sites: p->tmpl is still NULL there (kzalloc'd, not yet assigned) and nf_ct_put(NULL) is a no-op, so no inline release is needed.
CVE-2026-72429 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: ipv6: ioam: fix type confusion of dst_entry IOAM uses a dummy dst_entry(null_dst) to mark that the destination should not be changed after the transformation. This dst is stored in the IOAM lwt state and may be passed to dst_cache_set_ip6(). However, the IPv6 dst cache path eventually calls rt6_get_cookie(), which treats the dst_entry as part of a struct rt6_info. Since the null_dst was embedded directly as a struct dst_entry in struct ioam6_lwt, this resulted in an invalid cast and rt6_get_cookie() reading fields from the wrong object. In practice, the wrong cookie is not used while dst->obsolete is zero, but rt6_get_cookie() may also access per-cpu value when rt->sernum is zero. In this case, rt->sernum aliases ioam6_lwt::cache::reset_ts, which can become zero, making this a potential invalid pointer access. Fix this by embedding a full struct rt6_info for the dummy IPv6 route and passing its dst member to the dst APIs.
CVE-2026-72428 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix stack slot index in nospec checks check_stack_write_fixed_off() computes the byte slot for a fixed-offset stack write as -off - 1, and records each written byte in slot_type[] with (slot - i) % BPF_REG_SIZE. The Spectre v4 sanitization pre-check uses slot_type[i] instead. For a 4-byte write at fp-8 after the lower half of fp-8 has been zeroed, the pre-check scans bytes 0..3 and sees STACK_ZERO while the actual write updates bytes 7..4. That can leave the second half-slot write without nospec_result even though the bytes being overwritten still require sanitization. Use the same slot index in the sanitization pre-check that the write path uses when updating slot_type[].
CVE-2026-72427 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix effective prog array index with BPF_F_PREORDER replace_effective_prog() and purge_effective_progs() located the slot in the effective array by walking the program hlist and counting entries linearly. That count does not match the array layout: compute_effective_ progs() places BPF_F_PREORDER programs at the front (ancestor cgroup first, attach order within a cgroup) and the rest after them (descendant cgroup first). So when a preorder program is present, the linear hlist position no longer equals the program's index in the effective array. For replace_effective_prog() (bpf_link_update()) this overwrote the wrong slot, corrupting the effective order. For purge_effective_progs(), it could dummy out a slot belonging to a different program and leave the detached program in the array while bpf_prog_put() drops its reference, i.e. a use-after-free. Fix both by replaying compute_effective_progs()'s placement (including the per-cgroup preorder reversal) in a shared effective_prog_pos() helper. Identify the entry by its struct bpf_prog_list pointer rather than by (prog, link) value, so the lookup resolves to exactly the attachment the syscall selected even when the same bpf_prog is attached to several cgroups in the hierarchy.
CVE-2026-72426 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: bpf: Preserve pointer spill metadata during half-slot cleanup __clean_func_state() cleans dead stack slots in 4-byte halves. When the high half of a STACK_SPILL slot is dead and the low half remains live, cleanup converts the live low half to STACK_MISC or STACK_ZERO and clears the saved spilled_ptr metadata. That conversion is safe only for scalar spills. For a pointer spill, this metadata clear lets a later 32-bit fill from the still-live half avoid the normal non-scalar register-fill check and be treated as an ordinary scalar stack read. Leave non-scalar spill slots intact in this half-live shape. This is conservative for pruning and preserves the existing check_stack_read_fixed_off() rejection path for partial fills from pointer spills.
CVE-2026-72425 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: ice: fix FDIR CTRL VSI resource leak in ice_reset_all_vfs() Resetting all VFs causes resource leak on VFs with FDIR filters enabled as CTRL VSIs are only invalidated and not freed. Fix by using ice_vf_ctrl_vsi_release() instead of ice_vf_ctrl_invalidate_vsi() which aligns behavior with the ice_reset_vf() function. Reproduction: echo 1 > /sys/class/net/$pf/device/sriov_numvfs ethtool -N $vf flow-type ether proto 0x9000 action 0 echo 1 > /sys/class/net/$pf/device/reset
CVE-2026-72424 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: rtc: msc313: fix NULL deref in shared IRQ handler at probe msc313_rtc_probe() calls devm_request_irq() with IRQF_SHARED and &pdev->dev as the cookie, but platform_set_drvdata() is only called later after the clock setup. With a shared IRQ line, another device on the same line can trigger the handler in that window. The handler does dev_get_drvdata() on the cookie, gets NULL, and dereferences priv->rtc_base in interrupt context. Pass priv as the cookie directly so the handler reads it from dev_id without the lookup, removing the dependency on probe order.
CVE-2026-72423 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: bpf: Guard conntrack opts error writes The conntrack lookup and allocation kfuncs take an opts pointer together with an opts__sz argument. The verifier checks only the memory range described by opts__sz, but the wrappers unconditionally write opts->error whenever the internal lookup or allocation helper returns an error. For an invalid size smaller than the end of opts->error, that write can land outside the verifier-checked range. Keep returning NULL for invalid arguments, but only report the error through opts->error when the supplied size includes the field. This preserves error reporting for the supported 12-byte and 16-byte layouts, and for other invalid sizes that still include opts->error.
CVE-2026-72422 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix use-after-free of conn->preauth_info in concurrent SMB2 NEGOTIATE conn->preauth_info is shared connection state (struct preauth_integrity_info, kmalloc-96) that is allocated and freed by the SMB2 NEGOTIATE handler and read by the response send path. smb2_handle_negotiate() allocates conn->preauth_info, and on a deassemble_neg_contexts() failure kfrees it and sets it to NULL. Both the allocation and the free/NULL happen under ksmbd_conn_lock(conn) (the connection srv_mutex), which is held across the whole handler body. The response send path smb3_preauth_hash_rsp(), called from the send: block of __handle_ksmbd_work(), reads conn->preauth_info and dereferences conn->preauth_info->Preauth_HashValue (via ksmbd_gen_preauth_integrity_hash()) without taking conn_lock. When a client drives two SMB2 NEGOTIATE requests on the same connection, one worker can free conn->preauth_info on the failing-negotiate path while a concurrent send-path worker is reading it, producing a slab use-after-free read (KASAN-confirmed). The send-path read tested conn->preauth_info for NULL but raced with the free that occurs between the NULL check and the dereference, so the NULL guard alone does not close the window. Serialize the NEGOTIATE-branch read in smb3_preauth_hash_rsp() under ksmbd_conn_lock(conn) and re-check conn->preauth_info inside the lock. Because the negotiate handler holds conn_lock across its kfree + NULL assignment, a reader that also takes conn_lock either runs fully before the allocation or fully after the NULL store, and can never observe the freed-but-not-yet-NULLed pointer. ksmbd_gen_preauth_integrity_hash() takes no locks itself (it only computes a SHA-512 over the buffer), so no lock-ordering inversion is introduced, and conn_lock is a sleepable mutex which is safe on this send path (it already performs network I/O).
CVE-2026-72421 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: ipv4: fib: Don't ignore error route in local/main tables. When CONFIG_IP_MULTIPLE_TABLES is enabled but no rule is added, fib_lookup() performs route lookup directly on two tables. Since the first lookup does not properly bail out, the result of an error route in the merged local/main table could be overwritten by another route in the default table: # unshare -n # ip link set lo up # ip route add 192.168.0.0/24 dev lo table 253 # ip route add unreachable 192.168.0.0/24 # ip route get 192.168.0.1 192.168.0.1 dev lo table default uid 0 cache <local> Once a random rule is added, the error route is respected: # ip rule add table 0 # ip rule del table 0 # ip route get 192.168.0.1 RTNETLINK answers: No route to host Let's fix the inconsistent behaviour.
CVE-2026-72420 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: md/raid5: avoid R5_Overlap races while breaking stripe batches KCSAN report a race in break_stripe_batch_list() vs. raid5_make_request() on sh->dev[i].flags (plain word write vs. atomic bit op).. and .. one possible scenario is: CPU1 CPU2 break_stripe_batch_list(sh1) -> handle sh2 -> lock(sh2) -> sh2->batch_head = NULL -> unlock(sh2) -> test_and_clear_bit(R5_Overlap, sh2->dev[i].flags) -> wake_up_bit(sh2->dev[i].flags) raid5_make_request() -> add_all_stripe_bios(sh2) -> lock(sh2) -> stripe_bio_overlaps(sh2) returns true batch_head is NULL, so new bio overlap exist bio on sh2 -> true -> set_bit(R5_Overlap, sh2->dev[i].flags) -> unlock(sh2) -> wait_on_bit(sh2->dev[i].flags) -> sh2->dev[i].flags = sh1->dev[i].flags & ~R5_Overlap No wait_up_bit(), CPU2 could be wait_on_bit() forever... Fix by : - Expand the protect zone. - Use batch_head's device flag's snaphot when no held head_sh->stripe_lock. - Move sh/head_sh->batch_head = NULL to the end of protected zone , and , any concurrent add_all_stripe_bios() grabs sh->stripe_lock now either: - see batch_head != null, and , is rejected by stripe_bio_overlaps() under the lock (no R5_Overlap wait ) , or , - sees batch_head == NULL, only after dev[i].flags has already been set and the prior R5_Overlap waiters worken. KCSAN report: ================================================ BUG: KCSAN: data-race in break_stripe_batch_list / raid5_make_request write (marked) to 0xffff8e89c8117548 of 8 bytes by task 4042 on cpu 0: raid5_make_request+0xea0/0x2930 md_handle_request+0x4a2/0xa40 md_submit_bio+0x109/0x1a0 __submit_bio+0x2ec/0x390 submit_bio_noacct_nocheck+0x457/0x710 submit_bio_noacct+0x2a7/0xc20 submit_bio+0x56/0x250 blkdev_direct_IO+0x54c/0xda0 blkdev_write_iter+0x38f/0x570 aio_write+0x22b/0x490 io_submit_one+0xa51/0xf70 __x64_sys_io_submit+0xf7/0x220 x64_sys_call+0x1907/0x1c60 do_syscall_64+0x130/0x570 entry_SYSCALL_64_after_hwframe+0x76/0x7e read to 0xffff8e89c8117548 of 8 bytes by task 4010 on cpu 5: break_stripe_batch_list+0x249/0x480 handle_stripe_clean_event+0x720/0x9b0 handle_stripe+0x32fb/0x4500 handle_active_stripes.isra.0+0x6e0/0xa50 raid5d+0x7e0/0xba0 md_thread+0x15a/0x2d0 kthread+0x1e3/0x220 ret_from_fork+0x37a/0x410 ret_from_fork_asm+0x1a/0x30 value changed: 0x0000000000000019 -> 0x0000000000000099 --> R5_Overlap
CVE-2026-72419 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_nat: avoid invalid nat_net pointer use on failed nf_nat_init() We ran into below KASAN splat, which is mostly uninteresting, beside for having nf_nat_register_fn() in the call chain as a cause for the offending access: ================================================================== BUG: KASAN: slab-out-of-bounds in nf_nat_register_fn+0x5f9/0x640 Read of size 8 at addr ffff890031e54c20 by task iptables/9510 CPU: 0 UID: 0 PID: 9510 Comm: iptables Not tainted 6.18.18-grsec-full-20260320181326 #1 PREEMPT(voluntary) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Call Trace: <TASK> […] dump_stack_lvl+0xee/0x160 ffff88004117eeb8 […] print_report+0x6e/0x640 ffff88004117eee0 […] ? __phys_addr+0x8e/0x140 ffff88004117eef0 […] ? kasan_addr_to_slab+0x51/0xe0 ffff88004117ef08 […] ? complete_report_info+0xec/0x1c0 ffff88004117ef20 […] ? nf_nat_register_fn+0x5f9/0x640 ffff88004117ef48 […] kasan_report+0xbc/0x140 ffff88004117ef50 […] ? nf_nat_register_fn+0x5f9/0x640 ffff88004117ef90 […] nf_nat_register_fn+0x5f9/0x640 ffff88004117eff8 […] ? nf_nat_icmp_reply_translation+0x6e0/0x6e0 ffff88004117f070 […] nf_tables_register_hook.part.0+0xa0/0x220 ffff88004117f080 […] nf_tables_addchain.constprop.0+0x1054/0x1fc0 ffff88004117f0b8 […] ? nft_chain_lookup.part.0+0x4ce/0xac0 ffff88004117f130 […] ? nf_tables_abort+0x3d80/0x3d80 ffff88004117f190 […] ? nf_tables_dumpreset_obj+0x100/0x100 ffff88004117f1c8 […] ? nft_table_lookup.part.0+0x255/0x300 ffff88004117f310 […] ? nf_tables_newchain+0x21a4/0x2fa0 ffff88004117f358 […] nf_tables_newchain+0x21a4/0x2fa0 ffff88004117f360 […] ? nf_tables_addchain.constprop.0+0x1fc0/0x1fc0 ffff88004117f458 […] ? nla_get_range_signed+0x4a0/0x4a0 ffff88004117f488 […] ? lock_acquire+0x16f/0x320 ffff88004117f490 […] ? find_held_lock+0x3b/0xe0 ffff88004117f4b0 […] ? __nla_parse+0x45/0x80 ffff88004117f500 […] nfnetlink_rcv_batch+0xbca/0x19a0 ffff88004117f550 […] ? nfnetlink_net_exit_batch+0x120/0x120 ffff88004117f618 […] ? __sanitizer_cov_trace_switch+0x63/0xe0 ffff88004117f720 […] ? gr_acl_handle_mmap+0x1c4/0x320 ffff88004117f7c0 […] ? nla_get_range_signed+0x4a0/0x4a0 ffff88004117f7e8 […] ? gr_is_capable+0x6f/0xe0 ffff88004117f830 […] ? __nla_parse+0x45/0x80 ffff88004117f860 […] ? skb_pull+0x103/0x1a0 ffff88004117f880 […] nfnetlink_rcv+0x3db/0x4a0 ffff88004117f8b0 […] ? nfnetlink_rcv_batch+0x19a0/0x19a0 ffff88004117f8d8 […] ? netlink_lookup+0xe2/0x240 ffff88004117f900 […] netlink_unicast+0x74b/0xb00 ffff88004117f930 […] ? netlink_attachskb+0xb20/0xb20 ffff88004117f980 […] ? __check_object_size+0x3e/0xaa0 ffff88004117f998 […] ? security_netlink_send+0x51/0x160 ffff88004117f9c8 […] netlink_sendmsg+0xa03/0x1200 ffff88004117f9f8 […] ? netlink_unicast+0xb00/0xb00 ffff88004117fa70 […] ? netlink_unicast+0xb00/0xb00 ffff88004117fac8 […] ? ____sys_sendmsg+0xe2a/0x1040 ffff88004117faf8 […] ____sys_sendmsg+0xe2a/0x1040 ffff88004117fb00 […] ? kernel_recvmsg+0x300/0x300 ffff88004117fb60 […] ? reacquire_held_locks+0xe9/0x260 ffff88004117fbc8 […] ___sys_sendmsg+0x138/0x200 ffff88004117fbf8 […] ? do_recvmmsg+0x7e0/0x7e0 ffff88004117fc30 […] ? lockdep_hardirqs_on_prepare+0x101/0x1e0 ffff88004117fc50 […] ? lock_acquire+0x16f/0x320 ffff88004117fd20 […] ? lock_acquire+0x16f/0x320 ffff88004117fd58 […] ? find_held_lock+0x3b/0xe0 ffff88004117fd70 […] __sys_sendmsg+0x17a/0x260 ffff88004117fdc8 […] ? __sys_sendmsg_sock+0x80/0x80 ffff88004117fdf0 […] ? syscall_trace_enter+0x15e/0x2c0 ffff88004117fe98 […] do_syscall_64+0x7d/0x400 ffff88004117fec8 […] entry_SYSCALL_64_safe_stack+0x4a/0x60 ffff88004117fef8 </TASK> ================================================================== The out-of-bounds report, though, is a red herring as it is f ---truncated---
CVE-2026-72418 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conncount: prevent connlimit drops for early confirmed ct Commit 69894e5b4c5e ("netfilter: nft_connlimit: update the count if add was skipped") introduced a regression where packets for valid connections are dropped when using connlimit for soft-limiting scenarios. The issue occurs when a new connection reuses a socket currently in the TIME_WAIT state. In this scenario, the connection tracking entry is evaluated as already confirmed. Previously, __nf_conncount_add() assumed that if a connection was confirmed and did not originate from the loopback interface, it should skip the addition and return -EEXIST. Skipping the addition triggers a garbage collection run that cleans up the TIME_WAIT connection. Consequently, the active connection count drops to 0, which xt_connlimit mishandles, leading to the false rejection of the perfectly valid new connection. Fix this by replacing the interface check with protocol-agnostic state checks. We now skip the tree insertion and preserve the lockless garbage collection optimization only if the connection is IPS_ASSURED. This allows early-confirmed setup packets (such as reused TIME_WAIT sockets or locally generated SYN-ACKs) to be properly evaluated and counted without falsely dropping. The goto check_connections path is maintained to ensure these setup packets are deduplicated correctly. This has been tested with slowhttptest and HTTP server configured locally to ensure we are not breaking soft-limiting scenarios for local or external connections. In addition, it was tested with a OVS zone limit too.
CVE-2026-72417 1 Linux 1 Linux Kernel 2026-08-15 N/A
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-2026-72416 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_compat: ebtables emulation must reject non-bridge targets xtables targets return netfilter verdicts: NF_ACCEPT, NF_DROP, and so on. ebtables targets return incompatible verdicts: EBT_ACCEPT, EBT_DROP, ... We cannot allow fallback to NFPROTO_UNSPEC. ebtables doesn't permit this since 11ff7288beb2 ("netfilter: ebtables: reject non-bridge targets") but that commit missed the nft_compat layer.
CVE-2026-72415 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: ASoC: SDCA: Validate written enum value in ge_put_enum_double() ge_put_enum_double() passes the user-supplied enumeration index item[0] to snd_soc_enum_item_to_val() without checking it against the number of items in the enum: ret = snd_soc_enum_item_to_val(e, item[0]); snd_soc_enum_item_to_val() indexes the heap-allocated e->values[] array with that index (e->values is set from a devm_kcalloc() of e->items entries), so a control write with an out-of-range item[0] reads past the end of the values buffer. The bounds check in snd_soc_dapm_put_enum_double() only runs afterwards, so it does not prevent the read here. Reject an out-of-range item before using it, matching the other enum put handlers. This issue was pointed out by the Sashiko AI review bot while reviewing a related enum-validation series: https://lore.kernel.org/all/20260609125735.CEB651F00893@smtp.kernel.org/
CVE-2026-72414 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: net: dsa: sja1105: round up PTP perout pin duration pin_duration is converted from the user-provided period to SJA1105 clock ticks and is later passed as the cycle_time argument to future_base_time(). Very small period values may become zero after the conversion, which can lead to a division by zero in future_base_time(). Round zero pin_duration up to 1 tick so that the smallest unsupported periods use the minimum non-zero hardware duration instead of passing zero to future_base_time().
CVE-2026-72413 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: sctp: fix err_chunk memory leaks in INIT handling When sctp_verify_init() encounters unrecognized parameters, it allocates an err_chunk to report them. However, this chunk is leaked in several code paths: 1. In sctp_sf_do_5_1B_init(), if security_sctp_assoc_request() fails after sctp_verify_init() has populated err_chunk, the function returns immediately without freeing it. 2. In sctp_sf_do_unexpected_init(), the same leak occurs on the security_sctp_assoc_request() failure path. 3. In sctp_sf_do_unexpected_init(), on the success path after copying unrecognized parameters to the INIT-ACK, the function returns without freeing err_chunk, unlike sctp_sf_do_5_1B_init() which properly frees it. Fix all three leaks by adding sctp_chunk_free(err_chunk) calls before returning in the error paths and on the success path in sctp_sf_do_unexpected_init().
CVE-2026-72412 1 Linux 1 Linux Kernel 2026-08-15 N/A
In the Linux kernel, the following vulnerability has been resolved: s390/mm: Fix handling of _PAGE_UNUSED pte bit The _PAGE_UNUSED softbit should not really be lying around. Its sole purpose is to signal to try_to_unmap_one() and try_to_migrate_one() that the page can be discarded instead of being moved / swapped. KVM has no way to know why a page is being unmapped, so it sets the bit on userspace ptes corresponding to unused guest pages every time they get unmapped. KVM has no reasonable way to clear the bit once the page is in use again. While set_ptes() checks and clears the bit, other paths that set new ptes did not. This led to used pages being thrown out as if they were unused, causing guest corruption. Fix the issue by clearing the _PAGE_UNUSED bit for present ptes in set_pte(), i.e. whenever a present pte is getting set. The check in set_ptes() is then redundant and can be removed. Also fix gmap_helper_try_set_pte_unused() to only set the bit if the pte is present; the _PAGE_UNUSED bit is only defined for present ptes and thus should not be set for non-present ptes.