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[209.35.187.178]) by smtp.googlemail.com with ESMTPSA id 00721157ae682-8b19e53e20csm19210517b3.13.2026.10.27.14.53.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 Oct 2026 14:53:55 -0700 (PDT) Message-ID: <4b75bd04-d82b-44f6-87ad-c18225146a73@canonical.com> Date: Tue, 27 Oct 2026 14:53:54 -0700 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH security v1] apparmor: fix a use-after-free in aa_lookupn_ns() To: Binbin Deng <18983559317@163.com>, georgia.garcia@canonical.com, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com Cc: ryan.lee@canonical.com, cengiz.can@canonical.com, apparmor@lists.ubuntu.com, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260923054623.247634-1-18983559317@163.com> Content-Language: en-US From: John Johansen Autocrypt: addr=john.johansen@canonical.com; keydata= xsFNBE5mrPoBEADAk19PsgVgBKkImmR2isPQ6o7KJhTTKjJdwVbkWSnNn+o6Up5knKP1f49E BQlceWg1yp/NwbR8ad+eSEO/uma/K+PqWvBptKC9SWD97FG4uB4/caomLEU97sLQMtnvGWdx rxVRGM4anzWYMgzz5TZmIiVTZ43Ou5VpaS1Vz1ZSxP3h/xKNZr/TcW5WQai8u3PWVnbkjhSZ PHv1BghN69qxEPomrJBm1gmtx3ZiVmFXluwTmTgJOkpFol7nbJ0ilnYHrA7SX3CtR1upeUpM a/WIanVO96WdTjHHIa43fbhmQube4txS3FcQLOJVqQsx6lE9B7qAppm9hQ10qPWwdfPy/+0W 6AWtNu5ASiGVCInWzl2HBqYd/Zll93zUq+NIoCn8sDAM9iH+wtaGDcJywIGIn+edKNtK72AM gChTg/j1ZoWH6ZeWPjuUfubVzZto1FMoGJ/SF4MmdQG1iQNtf4sFZbEgXuy9cGi2bomF0zvy BJSANpxlKNBDYKzN6Kz09HUAkjlFMNgomL/cjqgABtAx59L+dVIZfaF281pIcUZzwvh5+JoG eOW5uBSMbE7L38nszooykIJ5XrAchkJxNfz7k+FnQeKEkNzEd2LWc3QF4BQZYRT6PHHga3Rg ykW5+1wTMqJILdmtaPbXrF3FvnV0LRPcv4xKx7B3fGm7ygdoowARAQABzStKb2huIEpvaGFu c2VuIDxqb2huLmpvaGFuc2VuQGNhbm9uaWNhbC5jb20+wsF3BBMBCgAhBQJOjRdaAhsDBQsJ CAcDBRUKCQgLBRYCAwEAAh4BAheAAAoJEAUvNnAY1cPYi0wP/2PJtzzt0zi4AeTrI0w3Rj8E Waa1NZWw4GGo6ehviLfwGsM7YLWFAI8JB7gsuzX/im16i9C3wHYXKs9WPCDuNlMc0rvivqUI JXHHfK7UHtT0+jhVORyyVVvX+qZa7HxdZw3jK+ROqUv4bGnImf31ll99clzo6HpOY59soa8y 66/lqtIgDckcUt/1ou9m0DWKwlSvulL1qmD25NQZSnvB9XRZPpPd4bea1RTa6nklXjznQvTm MdLq5aJ79j7J8k5uLKvE3/pmpbkaieEsGr+azNxXm8FPcENV7dG8Xpd0z06E+fX5jzXHnj69 DXXc3yIvAXsYZrXhnIhUA1kPQjQeNG9raT9GohFPMrK48fmmSVwodU8QUyY7MxP4U6jE2O9L 7v7AbYowNgSYc+vU8kFlJl4fMrX219qU8ymkXGL6zJgtqA3SYHskdDBjtytS44OHJyrrRhXP W1oTKC7di/bb8jUQIYe8ocbrBz3SjjcL96UcQJecSHu0qmUNykgL44KYzEoeFHjr5dxm+DDg OBvtxrzd5BHcIbz0u9ClbYssoQQEOPuFmGQtuSQ9FmbfDwljjhrDxW2DFZ2dIQwIvEsg42Hq 5nv/8NhW1whowliR5tpm0Z0KnQiBRlvbj9V29kJhs7rYeT/dWjWdfAdQSzfoP+/VtPRFkWLr 0uCwJw5zHiBgzsFNBE5mrPoBEACirDqSQGFbIzV++BqYBWN5nqcoR+dFZuQL3gvUSwku6ndZ vZfQAE04dKRtIPikC4La0oX8QYG3kI/tB1UpEZxDMB3pvZzUh3L1EvDrDiCL6ef93U+bWSRi GRKLnNZoiDSblFBST4SXzOR/m1wT/U3Rnk4rYmGPAW7ltfRrSXhwUZZVARyJUwMpG3EyMS2T dLEVqWbpl1DamnbzbZyWerjNn2Za7V3bBrGLP5vkhrjB4NhrufjVRFwERRskCCeJwmQm0JPD IjEhbYqdXI6uO+RDMgG9o/QV0/a+9mg8x2UIjM6UiQ8uDETQha55Nd4EmE2zTWlvxsuqZMgy W7gu8EQsD+96JqOPmzzLnjYf9oex8F/gxBSEfE78FlXuHTopJR8hpjs6ACAq4Y0HdSJohRLn 5r2CcQ5AsPEpHL9rtDW/1L42/H7uPyIfeORAmHFPpkGFkZHHSCQfdP4XSc0Obk1olSxqzCAm uoVmRQZ3YyubWqcrBeIC3xIhwQ12rfdHQoopELzReDCPwmffS9ctIb407UYfRQxwDEzDL+m+ TotTkkaNlHvcnlQtWEfgwtsOCAPeY9qIbz5+i1OslQ+qqGD2HJQQ+lgbuyq3vhefv34IRlyM sfPKXq8AUTZbSTGUu1C1RlQc7fpp8W/yoak7dmo++MFS5q1cXq29RALB/cfpcwARAQABwsFf BBgBCgAJBQJOZqz6AhsMAAoJEAUvNnAY1cPYP9cP/R10z/hqLVv5OXWPOcpqNfeQb4x4Rh4j h/jS9yjes4uudEYU5xvLJ9UXr0wp6mJ7g7CgjWNxNTQAN5ydtacM0emvRJzPEEyujduesuGy a+O6dNgi+ywFm0HhpUmO4sgs9SWeEWprt9tWrRlCNuJX+u3aMEQ12b2lslnoaOelghwBs8IJ r998vj9JBFJgdeiEaKJLjLmMFOYrmW197As7DTZ+R7Ef4gkWusYFcNKDqfZKDGef740Xfh9d yb2mJrDeYqwgKb7SF02Hhp8ZnohZXw8ba16ihUOnh1iKH77Ff9dLzMEJzU73DifOU/aArOWp JZuGJamJ9EkEVrha0B4lN1dh3fuP8EjhFZaGfLDtoA80aPffK0Yc1R/pGjb+O2Pi0XXL9AVe qMkb/AaOl21F9u1SOosciy98800mr/3nynvid0AKJ2VZIfOP46nboqlsWebA07SmyJSyeG8c XA87+8BuXdGxHn7RGj6G+zZwSZC6/2v9sOUJ+nOna3dwr6uHFSqKw7HwNl/PUGeRqgJEVu++ +T7sv9+iY+e0Y+SolyJgTxMYeRnDWE6S77g6gzYYHmcQOWP7ZMX+MtD4SKlf0+Q8li/F9GUL p0rw8op9f0p1+YAhyAd+dXWNKf7zIfZ2ME+0qKpbQnr1oizLHuJX/Telo8KMmHter28DPJ03 lT9Q Organization: Canonical In-Reply-To: <20260923054623.247634-1-18983559317@163.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/22/26 22:46, Binbin Deng wrote: > aa_lookupn_ns() takes a reference on the namespace it finds with > aa_get_ns(),which is kref_get() on the reference count that the > namespace is released through, without checking whether the namespace > is still in use. A concurrent removal of a ":"-prefixed namespace > looks the same namespace up and only then takes the parent lock to > remove it, so the last reference can be dropped between the lookup and > the aa_get_ns() call: the reference count then reports the increment on > a zero count and the kernel classifies the following use of the object > as a use-after-free. A user with CAP_MAC_ADMIN can trigger this by > writing a ":" removal and a ":/" removal to > /sys/kernel/security/apparmor/.remove concurrently. > > refcount_t: addition on 0; use-after-free. > WARNING: lib/refcount.c:25 at refcount_warn_saturate+0xc0/0xe0, CPU#6 > Call Trace: > > aa_lookupn_ns+0xa9/0xc0 > aa_remove_profiles+0x4fb/0x730 > ? __kvmalloc_node_noprof+0x219/0x5c0 > ? __pfx_aa_remove_profiles+0x10/0x10 > ? aa_loaddata_alloc+0x65/0x1f0 > ? _copy_from_user+0x2d/0x80 > ? aa_loaddata_alloc+0x111/0x1f0 > profile_remove+0x2ee/0x4a0 > vfs_write+0x21e/0xcf0 > ? rcu_core+0x29c/0x1740 > ? timerqueue_linked_add+0x1f4/0x3d0 > ? __pfx_vfs_write+0x10/0x10 > ? mutex_lock+0x81/0xe0 > ? __pfx_mutex_lock+0x10/0x10 > ? __pfx_rcu_core+0x10/0x10 > ? __pfx_hrtimer_update_next_event+0x10/0x10 > ? mutex_unlock+0x7b/0xd0 > ? fdget_pos+0x24d/0x4b0 > ksys_write+0xf7/0x1c0 > ? __pfx_ksys_write+0x10/0x10 > ? restore_fpregs_from_fpstate+0x37/0xc0 > do_syscall_64+0xf9/0x540 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > Fix by rejecting a namespace whose reference count. > > Fixes: 3664268f19ea0 ("apparmor: add namespace lookup fns()") > Signed-off-by: Binbin Deng <18983559317@163.com> Acked-by: John Johansen > --- > security/apparmor/include/policy_ns.h | 16 ++++++++++++++++ > security/apparmor/policy_ns.c | 2 +- > 2 files changed, 17 insertions(+), 1 deletion(-) > > diff --git a/security/apparmor/include/policy_ns.h b/security/apparmor/include/policy_ns.h > index cc6e84151812..4f8359875476 100644 > --- a/security/apparmor/include/policy_ns.h > +++ b/security/apparmor/include/policy_ns.h > @@ -117,6 +117,22 @@ static inline struct aa_ns *aa_get_ns(struct aa_ns *ns) > return ns; > } > > +/** > + * aa_get_ns_not0 - increment references count on @ns found via lookup > + * @ns: namespace to increment reference count of (MAYBE NULL) > + * > + * Returns: pointer to @ns, if @ns is NULL returns NULL, > + * NULL if @ns is being freed > + * Requires: @ns must be held with valid refcount when called > + */ > +static inline struct aa_ns *aa_get_ns_not0(struct aa_ns *ns) > +{ > + if (ns && aa_get_profile_not0(ns->unconfined)) > + return ns; > + > + return NULL; > +} > + > /** > * aa_put_ns - decrement refcount on @ns > * @ns: namespace to put reference of > diff --git a/security/apparmor/policy_ns.c b/security/apparmor/policy_ns.c > index 5a907a875d8f..ae9168c1a85e 100644 > --- a/security/apparmor/policy_ns.c > +++ b/security/apparmor/policy_ns.c > @@ -207,7 +207,7 @@ struct aa_ns *aa_lookupn_ns(struct aa_ns *view, const char *name, size_t n) > struct aa_ns *ns = NULL; > > rcu_read_lock(); > - ns = aa_get_ns(__aa_lookupn_ns(view, name, n)); > + ns = aa_get_ns_not0(__aa_lookupn_ns(view, name, n)); > rcu_read_unlock(); > > return ns;