From: John Johansen <john.johansen@canonical.com> mainline inclusion from mainline-v7.3-rc1 commit 4ec11f14d1d6fdda787d991b142537be7841d395 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/19429 CVE: CVE-2026-90179 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- 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 reference is put, and then used for the next lookup. The mutex_lock, will block replacement, and removal in the locked ns. However there are two cases where putting the reference can result in the label being freed even with the lock held. 1. the label does not have a list reference (possible for temporary or special profiles) in which case the put can trigger the cleanup. 2. the new label reference is in a different namespace, which does not have a lock held on it. This extends case 1 to also include replacement, and removal that could be occurring in the namespace new is in. Reported-by: Martin Petricek <mp@petricek.net> Link: https://lists.ubuntu.com/archives/apparmor/2026-August/014907.html Fixes: 32e92764d6f8d ("apparmor: grab ns lock and refresh when looking up changehat child profiles") Signed-off-by: John Johansen <john.johansen@canonical.com> Conflicts: security/apparmor/domain.c security/apparmor/policy.c [1)Context lines differ: hulk-6.6 uses label_for_each_in_ns rather than label_for_each_in_scope and the build path lacks the AA_BUG and blank line, both from mainline commits not backported; the needput put was placed directly between mutex_unlock and return. 2)Context lines differ: hulk-6.6 __aa_new_learning_profile has different local variables (no name_sz, uses kmalloc/sprintf rather than snprintf) from mainline commits not backported; only the mutex_is_locked assertion was added] Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com> --- security/apparmor/domain.c | 25 +++++++++++++++++-------- security/apparmor/include/policy.h | 3 +++ security/apparmor/policy.c | 22 +++++++++++++++++----- 3 files changed, 37 insertions(+), 13 deletions(-) diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c index 0a4dd74c3050..4e0081cfd648 100644 --- a/security/apparmor/domain.c +++ b/security/apparmor/domain.c @@ -1029,8 +1029,8 @@ static struct aa_label *build_change_hat(const struct cred *subj_cred, if (!hat) { error = -ENOENT; if (COMPLAIN_MODE(profile)) { - hat = aa_new_learning_profile(profile, true, name, - GFP_KERNEL); + hat = __aa_new_learning_profile(profile, true, name, + GFP_KERNEL); if (!hat) { info = "failed null profile create"; error = -ENOMEM; @@ -1068,6 +1068,7 @@ static struct aa_label *change_hat(const struct cred *subj_cred, bool sibling = false; const char *name, *info = NULL; int i, error; + bool needput = false; AA_BUG(!label); AA_BUG(!hats); @@ -1080,7 +1081,6 @@ static struct aa_label *change_hat(const struct cred *subj_cred, * the profiles and label, we can rely on the namespaces being live * and avoid incrementing their refcounts while grabbing the lock. */ - label = aa_get_label(label); ns = labels_ns(label); retry: @@ -1088,15 +1088,19 @@ static struct aa_label *change_hat(const struct cred *subj_cred, if (label_is_stale(label)) { new = aa_get_newest_label(label); new_ns = labels_ns(new); + + if (needput) + /* aa_put_label() is safe to call when under lock */ + aa_put_label(label); + label = new; + needput = true; + /* check if replaced with label in parent ns, and lock there */ if (new_ns != ns) { - aa_put_label(new); mutex_unlock(&ns->lock); ns = new_ns; - label = new; + /* retry will bottom out at the root of the tree */ goto retry; } - aa_put_label(label); - label = new; } if (PROFILE_IS_HAT(labels_profile(label))) @@ -1107,7 +1111,8 @@ static struct aa_label *change_hat(const struct cred *subj_cred, name = hats[i]; label_for_each_in_ns(it, labels_ns(label), label, profile) { if (sibling && PROFILE_IS_HAT(profile)) { - root = aa_get_profile(profile->parent); + root = aa_get_profile(rcu_dereference_protected(profile->parent, + mutex_is_locked(&ns->lock))); } else if (!sibling && !PROFILE_IS_HAT(profile)) { root = aa_get_profile(profile); } else { /* conflicting change type */ @@ -1168,6 +1173,8 @@ static struct aa_label *change_hat(const struct cred *subj_cred, } } mutex_unlock(&ns->lock); + if (needput) + aa_put_label(label); return ERR_PTR(error); build: @@ -1181,6 +1188,8 @@ static struct aa_label *change_hat(const struct cred *subj_cred, goto fail; } /* else if (IS_ERR) build_change_hat has logged error so return new */ mutex_unlock(&ns->lock); + if (needput) + aa_put_label(label); return new; } diff --git a/security/apparmor/include/policy.h b/security/apparmor/include/policy.h index 98dab531fe26..d0bf70669596 100644 --- a/security/apparmor/include/policy.h +++ b/security/apparmor/include/policy.h @@ -236,6 +236,9 @@ struct aa_profile *aa_alloc_profile(const char *name, struct aa_proxy *proxy, gfp_t gfp); struct aa_profile *aa_alloc_null(struct aa_profile *parent, const char *name, gfp_t gfp); +struct aa_profile *__aa_new_learning_profile(struct aa_profile *parent, + bool hat, const char *base, + gfp_t gfp); struct aa_profile *aa_new_learning_profile(struct aa_profile *parent, bool hat, const char *base, gfp_t gfp); void aa_free_profile(struct aa_profile *profile); diff --git a/security/apparmor/policy.c b/security/apparmor/policy.c index 0c6e255cb0a4..c917b29f83dd 100644 --- a/security/apparmor/policy.c +++ b/security/apparmor/policy.c @@ -642,7 +642,7 @@ struct aa_profile *aa_alloc_null(struct aa_profile *parent, const char *name, } /** - * aa_new_learning_profile - create or find a null-X learning profile + * __aa_new_learning_profile - create or find a null-X learning profile * @parent: profile that caused this profile to be created (NOT NULL) * @hat: true if the null- learning profile is a hat * @base: name to base the null profile off of @@ -659,14 +659,16 @@ struct aa_profile *aa_alloc_null(struct aa_profile *parent, const char *name, * * Returns: new refcounted profile else NULL on failure */ -struct aa_profile *aa_new_learning_profile(struct aa_profile *parent, bool hat, - const char *base, gfp_t gfp) +struct aa_profile *__aa_new_learning_profile(struct aa_profile *parent, + bool hat, const char *base, + gfp_t gfp) { struct aa_profile *p, *profile; const char *bname; char *name = NULL; AA_BUG(!parent); + AA_BUG(!mutex_is_locked(&parent->ns->lock)); if (base) { name = kmalloc(strlen(parent->base.hname) + 8 + strlen(base), @@ -698,7 +700,6 @@ struct aa_profile *aa_new_learning_profile(struct aa_profile *parent, bool hat, if (hat) profile->label.flags |= FLAG_HAT; - mutex_lock_nested(&profile->ns->lock, profile->ns->level); p = __find_child(&parent->base.profiles, bname); if (p) { aa_free_profile(profile); @@ -706,7 +707,6 @@ struct aa_profile *aa_new_learning_profile(struct aa_profile *parent, bool hat, } else { __add_profile(&parent->base.profiles, profile); } - mutex_unlock(&profile->ns->lock); /* refcount released by caller */ out: @@ -720,6 +720,18 @@ struct aa_profile *aa_new_learning_profile(struct aa_profile *parent, bool hat, return NULL; } +struct aa_profile *aa_new_learning_profile(struct aa_profile *parent, bool hat, + const char *base, gfp_t gfp) +{ + struct aa_profile *profile; + + mutex_lock_nested(&parent->ns->lock, parent->ns->level); + profile = __aa_new_learning_profile(parent, hat, base, gfp); + mutex_unlock(&parent->ns->lock); + + return profile; +} + /** * replacement_allowed - test to see if replacement is allowed * @profile: profile to test if it can be replaced (MAYBE NULL) -- 2.43.0