In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
apparmor: fix deadlock in complain-mode change_hat<\/p>\n
The use of change_hat when in complain mode can cause a deadlock
\nwhen the hat doesn’t exist and a new learning profile is created
\nfor the missing profile. This is because change_hat() has taken
\nthe lock to search the hat list and creating the new learning
\nprofile needs to take the lock to add it to the list.<\/p>\n
From the bug report:<\/p>\n
Originally found in 7.0.0 in LTS ubuntu 26.04 with pam_apparmor + su
\nin complain mode set to change hats. Then verified in newest
\navailable vanilla kernel I’ve compiled to see if still present:<\/p>\n
7.2-rc7 vanilla -> affected<\/p>\n
checked also some other kernels:
\n6.18.44 vanilla -> affected
\n6.12.95 with debian patches -> unaffected<\/p>\n
On systems without bug (for example 6.12.95 debian) it just prints:<\/p>\n
aa_change_hat rc=0<\/p>\n
On systems with bug, the executable always hangs, prints nothing and
\nbecomes unkillable. (And once stuck this way, it will cause any
\nfurther hat changes to also cause the changing process to get stuck)<\/p>\n
Then in syslog you can find hint about cause:<\/p>\n
kernel: INFO: task hat:3409 blocked for more than 483 seconds.
\nkernel: Not tainted 7.2.0-rc7 #1
\nkernel: “echo 0 > \/proc\/sys\/kernel\/hung_task_timeout_secs” disables this message.
\nkernel: task:hat state:D stack:0 pid:3409 tgid:3409 ppid:2605 task_flags:0x400000 flags:0x00080800
\nkernel: Call Trace:
\nkernel:
\nkernel: __schedule+0x48f\/0xfe0
\nkernel: schedule+0x27\/0xa0
\nkernel: schedule_preempt_disabled+0x15\/0x30
\nkernel: __mutex_lock.constprop.0+0x569\/0xa10
\nkernel: aa_new_learning_profile+0x15f\/0x210
\nkernel: build_change_hat+0x19f\/0x3b0
\nkernel: change_hat.isra.0+0x5dd\/0xd60
\nkernel: aa_change_hat+0x2f3\/0x710
\nkernel: aa_setprocattr_changehat+0x121\/0x1f0
\nkernel: do_setattr+0x28c\/0x340
\nkernel: apparmor_setselfattr+0x20\/0x50
\nkernel: security_setselfattr+0xf6\/0x110
\nkernel: __x64_sys_lsm_set_self_attr+0x53\/0x90
\nkernel: do_syscall_64+0xdd\/0x5e0
\nkernel: ? __mod_memcg_lruvec_state+0xfd\/0x260
\nkernel: ? lruvec_stat_mod_folio+0x8d\/0xd0
\nkernel: ? __folio_mod_stat+0x2d\/0x90
\nkernel: ? map_anon_folio_pte_nopf+0xd1\/0x1f0
\nkernel: ? do_anonymous_page+0x184\/0xa10
\nkernel: ? __handle_mm_fault+0x805\/0x870
\nkernel: ? count_memcg_events+0xef\/0x230
\nkernel: ? handle_mm_fault+0x1f0\/0x2f0
\nkernel: ? do_user_addr_fault+0x2bb\/0x7b0
\nkernel: ? do_syscall_64+0x94\/0x5e0
\nkernel: ? exc_page_fault+0x75\/0x160
\nkernel: entry_SYSCALL_64_after_hwframe+0x76\/0x7e
\nkernel: RIP: 0033:0x7f815e134c8d
\nkernel: RSP: 002b:00007fff6df94ea8 EFLAGS: 00000246 ORIG_RAX: 00000000000001cc
\nkernel: RAX: ffffffffffffffda RBX: 0000556d8c81d040 RCX: 00007f815e134c8d
\nkernel: RDX: 0000000000000046 RSI: 0000556d8c81d040 RDI: 0000000000000064
\nkernel: RBP: 00007fff6df94ef0 R08: 00007f815e212ac8 R09: 000000000000000c
\nkernel: R10: 0000000000000000 R11: 0000000000000246 R12: 0000556d8c81d010
\nkernel: R13: 0000000000000026 R14: 0000000000000046 R15: 0000000000000064
\nkernel:
\nkernel: INFO: task hat:3409 is blocked on a mutex likely owned by task hat:3409.<\/p>\n
To fix the issue, lift the locking out of the core of
\naa_new_learning_profile(), introduce a wrapper function that takes the
\nlock where needed, and have build_change_hat() call the core function
\nthat no longer takes the lock.<\/p>\n
In addition fix 4 other issues introduced by commit
\n32e92764d6f8d (“apparmor: grab ns lock and refresh when looking up changehat child profiles”)
\n– aa_get_profile_rcu() was replaced-by: aa_get_profile without the
\n accompanying rcu_dereference_protected()
\n– an extra aa_get_label(label) was introduced at the start of
\n change_hat() without an accompanying aa_put_label() causing a
\n reference count leak.
\n– a reference count leak was introduced in the label_is_stale(label)
\n case, where the newest profile would be leaked instead of the
\n label passed to the function.
\n– a potential UAF when the lookup walks up the tree with new_ns != ns
\n the new label refere
\n—truncated—<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
apparmor: fix deadlock in complain-mode change_hat<\/p>\n
The use of change_hat when in complain mode can cause a deadlock
\nwhen the hat d<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-25588","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/25588","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=25588"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=25588"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=25588"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}