In the Linux kernel, the following vulnerability has been resolved: apparmor: fix deadlock in complain-mode change_hat The use of change_hat when in complain mode can cause a deadlock when the hat doesn't exist and a new learning profile is created for the missing profile. This is because change_hat() has taken the lock to search the hat list and creating the new learning profile needs to take the lock to add it to the list. From the bug report: Originally found in 7.0.0 in LTS ubuntu 26.04 with pam_apparmor + su in complain mode set to change hats. Then verified in newest available vanilla kernel I've compiled to see if still present: 7.2-rc7 vanilla -> affected checked also some other kernels: 6.18.44 vanilla -> affected 6.12.95 with debian patches -> unaffected On systems without bug (for example 6.12.95 debian) it just prints: aa_change_hat rc=0 On systems with bug, the executable always hangs, prints nothing and becomes unkillable. (And once stuck this way, it will cause any further hat changes to also cause the changing process to get stuck) Then in syslog you can find hint about cause: kernel: INFO: task hat:3409 blocked for more than 483 seconds. kernel: Not tainted 7.2.0-rc7 #1 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. kernel: task:hat state:D stack:0 pid:3409 tgid:3409 ppid:2605 task_flags:0x400000 flags:0x00080800 kernel: Call Trace: kernel: <TASK> kernel: __schedule+0x48f/0xfe0 kernel: schedule+0x27/0xa0 kernel: schedule_preempt_disabled+0x15/0x30 kernel: __mutex_lock.constprop.0+0x569/0xa10 kernel: aa_new_learning_profile+0x15f/0x210 kernel: build_change_hat+0x19f/0x3b0 kernel: change_hat.isra.0+0x5dd/0xd60 kernel: aa_change_hat+0x2f3/0x710 kernel: aa_setprocattr_changehat+0x121/0x1f0 kernel: do_setattr+0x28c/0x340 kernel: apparmor_setselfattr+0x20/0x50 kernel: security_setselfattr+0xf6/0x110 kernel: __x64_sys_lsm_set_self_attr+0x53/0x90 kernel: do_syscall_64+0xdd/0x5e0 kernel: ? __mod_memcg_lruvec_state+0xfd/0x260 kernel: ? lruvec_stat_mod_folio+0x8d/0xd0 kernel: ? __folio_mod_stat+0x2d/0x90 kernel: ? map_anon_folio_pte_nopf+0xd1/0x1f0 kernel: ? do_anonymous_page+0x184/0xa10 kernel: ? __handle_mm_fault+0x805/0x870 kernel: ? count_memcg_events+0xef/0x230 kernel: ? handle_mm_fault+0x1f0/0x2f0 kernel: ? do_user_addr_fault+0x2bb/0x7b0 kernel: ? do_syscall_64+0x94/0x5e0 kernel: ? exc_page_fault+0x75/0x160 kernel: entry_SYSCALL_64_after_hwframe+0x76/0x7e kernel: RIP: 0033:0x7f815e134c8d kernel: RSP: 002b:00007fff6df94ea8 EFLAGS: 00000246 ORIG_RAX: 00000000000001cc kernel: RAX: ffffffffffffffda RBX: 0000556d8c81d040 RCX: 00007f815e134c8d kernel: RDX: 0000000000000046 RSI: 0000556d8c81d040 RDI: 0000000000000064 kernel: RBP: 00007fff6df94ef0 R08: 00007f815e212ac8 R09: 000000000000000c kernel: R10: 0000000000000000 R11: 0000000000000246 R12: 0000556d8c81d010 kernel: R13: 0000000000000026 R14: 0000000000000046 R15: 0000000000000064 kernel: </TASK> kernel: INFO: task hat:3409 is blocked on a mutex likely owned by task hat:3409. To fix the issue, lift the locking out of the core of aa_new_learning_profile(), introduce a wrapper function that takes the lock where needed, and have build_change_hat() call the core function that no longer takes the lock. In addition fix 4 other issues introduced by commit 32e92764d6f8d ("apparmor: grab ns lock and refresh when looking up changehat child profiles") - aa_get_profile_rcu() was replaced-by: aa_get_profile without the accompanying rcu_dereference_protected() - an extra aa_get_label(label) was introduced at the start of change_hat() without an accompanying aa_put_label() causing a reference count leak. - a reference count leak was introduced in the label_is_stale(label) case, where the newest profile would be leaked instead of the label passed to the function. - a potential UAF when the lookup walks up the tree with new_ns != ns the new label refere ---truncated---

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - In the Linux kernel, the following vulnerability has been resolved: apparmor: fix deadlock in complain-
    mode change_hat The use of change_hat when in complain mode can cause a deadlock when the hat doesn't
    exist and a new learning profile is created for the missing profile. This is because change_hat() has
    taken the lock to search the hat list and creating the new learning profile needs to take the lock to add
    it to the list. From the bug report: Originally found in 7.0.0 in LTS ubuntu 26.04 with pam_apparmor + su
    in complain mode set to change hats. Then verified in newest available vanilla kernel I've compiled to see
    if still present: 7.2-rc7 vanilla -> affected checked also some other kernels: 6.18.44 vanilla -> affected
    6.12.95 with debian patches -> unaffected On systems without bug (for example 6.12.95 debian) it just
    prints: aa_change_hat rc=0 On systems with bug, the executable always hangs, prints nothing and becomes
    unkillable. (And once stuck this way, it will cause any further hat changes to also cause the changing
    process to get stuck) Then in syslog you can find hint about cause: kernel: INFO: task hat:3409 blocked
    for more than 483 seconds. kernel: Not tainted 7.2.0-rc7 #1 kernel: "echo 0 >
    /proc/sys/kernel/hung_task_timeout_secs" disables this message. kernel: task:hat state:D stack:0 pid:3409
    tgid:3409 ppid:2605 task_flags:0x400000 flags:0x00080800 kernel: Call Trace: kernel: <TASK> kernel:
    __schedule+0x48f/0xfe0 kernel: schedule+0x27/0xa0 kernel: schedule_preempt_disabled+0x15/0x30 kernel:
    __mutex_lock.constprop.0+0x569/0xa10 kernel: aa_new_learning_profile+0x15f/0x210 kernel:
    build_change_hat+0x19f/0x3b0 kernel: change_hat.isra.0+0x5dd/0xd60 kernel: aa_change_hat+0x2f3/0x710
    kernel: aa_setprocattr_changehat+0x121/0x1f0 kernel: do_setattr+0x28c/0x340 kernel:
    apparmor_setselfattr+0x20/0x50 kernel: security_setselfattr+0xf6/0x110 kernel:
    __x64_sys_lsm_set_self_attr+0x53/0x90 kernel: do_syscall_64+0xdd/0x5e0 kernel: ?
    __mod_memcg_lruvec_state+0xfd/0x260 kernel: ? lruvec_stat_mod_folio+0x8d/0xd0 kernel: ?
    __folio_mod_stat+0x2d/0x90 kernel: ? map_anon_folio_pte_nopf+0xd1/0x1f0 kernel: ?
    do_anonymous_page+0x184/0xa10 kernel: ? __handle_mm_fault+0x805/0x870 kernel: ?
    count_memcg_events+0xef/0x230 kernel: ? handle_mm_fault+0x1f0/0x2f0 kernel: ?
    do_user_addr_fault+0x2bb/0x7b0 kernel: ? do_syscall_64+0x94/0x5e0 kernel: ? exc_page_fault+0x75/0x160
    kernel: entry_SYSCALL_64_after_hwframe+0x76/0x7e kernel: RIP: 0033:0x7f815e134c8d kernel: RSP:
    002b:00007fff6df94ea8 EFLAGS: 00000246 ORIG_RAX: 00000000000001cc kernel: RAX: ffffffffffffffda RBX:
    0000556d8c81d040 RCX: 00007f815e134c8d kernel: RDX: 0000000000000046 RSI: 0000556d8c81d040 RDI:
    0000000000000064 kernel: RBP: 00007fff6df94ef0 R08: 00007f815e212ac8 R09: 000000000000000c kernel: R10:
    0000000000000000 R11: 0000000000000246 R12: 0000556d8c81d010 kernel: R13: 0000000000000026 R14:
    0000000000000046 R15: 0000000000000064 kernel: </TASK> kernel: INFO: task hat:3409 is blocked on a mutex
    likely owned by task hat:3409. To fix the issue, lift the locking out of the core of
    aa_new_learning_profile(), introduce a wrapper function that takes the lock where needed, and have
    build_change_hat() call the core function that no longer takes the lock. In addition fix 4 other issues
    introduced by commit 32e92764d6f8d ("apparmor: grab ns lock and refresh when looking up changehat child
    profiles") - aa_get_profile_rcu() was replaced-by: aa_get_profile without the accompanying
    rcu_dereference_protected() - an extra aa_get_label(label) was introduced at the start of change_hat()
    without an accompanying aa_put_label() causing a reference count leak. - a reference count leak was
    introduced in the label_is_stale(label) case, where the newest profile would be leaked instead of the
    label passed to the function. - a potential UAF when the lookup walks up the tree with new_ns != ns the
    new label refere ---truncated--- (CVE-2026-90179)

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - apparmor: fix deadlock in complain-mode change_hat The use of change_hat when in complain mode can cause a     deadlock when the hat doesn't exist and a new learning profile is created for the missing profile. This is     because change_hat() has taken the lock to search the hat list and creating the new learning profile needs     to take the lock to add it to the list. From the bug report: Originally found in 7.0.0 in LTS ubuntu 26.04     with pam_apparmor + su in complain mode set to change hats. Then verified in newest available vanilla     kernel I've compiled to see if still present: 7.2-rc7 vanilla -> affected checked also some other kernels:
    6.18.44 vanilla -> affected 6.12.95 with debian patches -> unaffected On systems without bug (for example     6.12.95 debian) it just prints: aa_change_hat rc=0 On systems with bug, the executable always hangs,     prints nothing and becomes unkillable. (And once stuck this way, it will cause any further hat changes to     also cause the changing process to get stuck) Then in syslog you can find hint about cause: kernel: INFO:
    task hat:3409 blocked for more than 483 seconds. kernel: Not tainted 7.2.0-rc7 #1 kernel: echo 0 >     /proc/sys/kernel/hung_task_timeout_secs disables this message. kernel: task:hat state:D stack:0 pid:3409     tgid:3409 ppid:2605 task_flags:0x400000 flags:0x00080800 kernel: Call Trace: kernel: <TASK> kernel:
    __schedule+0x48f/0xfe0 kernel: schedule+0x27/0xa0 kernel: schedule_preempt_disabled+0x15/0x30 kernel:
    __mutex_lock.constprop.0+0x569/0xa10 kernel: aa_new_learning_profile+0x15f/0x210 kernel:
    build_change_hat+0x19f/0x3b0 kernel: change_hat.isra.0+0x5dd/0xd60 kernel: aa_change_hat+0x2f3/0x710     kernel: aa_setprocattr_changehat+0x121/0x1f0 kernel: do_setattr+0x28c/0x340 kernel:
    apparmor_setselfattr+0x20/0x50 kernel: security_setselfattr+0xf6/0x110 kernel:
    __x64_sys_lsm_set_self_attr+0x53/0x90 kernel: do_syscall_64+0xdd/0x5e0 kernel: ?
    __mod_memcg_lruvec_state+0xfd/0x260 kernel: ? lruvec_stat_mod_folio+0x8d/0xd0 kernel: ?
    __folio_mod_stat+0x2d/0x90 kernel: ? map_anon_folio_pte_nopf+0xd1/0x1f0 kernel: ?     do_anonymous_page+0x184/0xa10 kernel: ? __handle_mm_fault+0x805/0x870 kernel: ?     count_memcg_events+0xef/0x230 kernel: ? handle_mm_fault+0x1f0/0x2f0 kernel: ?     do_user_addr_fault+0x2bb/0x7b0 kernel: ? do_syscall_64+0x94/0x5e0 kernel: ? exc_page_fault+0x75/0x160     kernel: entry_SYSCALL_64_after_hwframe+0x76/0x7e kernel: RIP: 0033:0x7f815e134c8d kernel: RSP:
    002b:00007fff6df94ea8 EFLAGS: 00000246 ORIG_RAX: 00000000000001cc kernel: RAX: ffffffffffffffda RBX:
    0000556d8c81d040 RCX: 00007f815e134c8d kernel: RDX: 0000000000000046 RSI: 0000556d8c81d040 RDI:
    0000000000000064 kernel: RBP: 00007fff6df94ef0 R08: 00007f815e212ac8 R09: 000000000000000c kernel: R10:
    0000000000000000 R11: 0000000000000246 R12: 0000556d8c81d010 kernel: R13: 0000000000000026 R14:
    0000000000000046 R15: 0000000000000064 kernel: </TASK> kernel: INFO: task hat:3409 is blocked on a mutex     likely owned by task hat:3409. To fix the issue, lift the locking out of the core of     aa_new_learning_profile(), introduce a wrapper function that takes the lock where needed, and have     build_change_hat() call the core function that no longer takes the lock. In addition fix 4 other issues     introduced by commit 32e92764d6f8d (apparmor: grab ns lock and refresh when looking up changehat child     profiles) - aa_get_profile_rcu() was replaced-by: aa_get_profile without the accompanying     rcu_dereference_protected() - an extra aa_get_label(label) was introduced at the start of change_hat()     without an accompanying aa_put_label() causing a reference count leak. - a reference count leak was     introduced in the label_is_stale(label) case, where the newest profile would be leaked instead of the     label passed to the function. - a potential UAF when the lookup walks up the tree with new_ns != ns the     new label refere ---truncated--- (CVE-2026-90179)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
376443	Ubuntu 24.04 LTS / 26.04 LTS : Linux kernel vulnerabilities (USN-8959-1)	Nessus	Ubuntu Local Security Checks	Local	high
475803	Google: sys-kernel/cchost-kernel-6_18, sys-kernel/csql-kernel-6_18, sys-kernel/lakitu-kernel-6_18, sys-kernel/lakitu-nc-kernel-6_18: security update to 20198.0.0	Tenable Cloud Security	Google COS Security Checks	Local	high
475803	Google: sys-kernel/cchost-kernel-6_18, sys-kernel/csql-kernel-6_18, sys-kernel/lakitu-kernel-6_18, sys-kernel/lakitu-nc-kernel-6_18: security update to 20198.0.0	Tenable Self-Hosted Container Security	Google COS Security Checks	Local	high
347578	Linux Distros Unpatched Vulnerability : CVE-2026-90179	Nessus	Misc.	Local	high

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