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Tue, 04 Aug 2026 05:58:41 -0700 (PDT) From: Benjamin Coddington X-Google-Original-From: Benjamin Coddington To: Vasileios Almpanis Cc: Trond Myklebust , Anna Schumaker , Benjamin Coddington , Trond Myklebust , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] NFS: sysfs: fix use-after-free on delayed kobject release Date: Tue, 04 Aug 2026 08:58:39 -0400 X-Mailer: MailMate (2.0r6272) Message-ID: <4FA2A276-5C44-4D7E-8C33-1322A7BB8AB4@hammerspace.com> In-Reply-To: <20260803-nfs-v1-1-034176dab4a3@gmail.com> References: <20260803-nfs-v1-1-034176dab4a3@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On 3 Aug 2026, at 5:18, Vasileios Almpanis wrote: > struct nfs_netns_client embeds two kobjects and is freed by > nfs_netns_object_release(), the release function of nfs_net_kobj. > Despite that the first one, p->kobject lives in the same allocation. > Nothing keeps the allocation from being freed before p->kobject > has been released. > > When CONFIG_DEBUG_KOBJECT_RELEASE=3Dy each release is instead deferred = to > a delayed_work embedded in the kobject, with an independent random > delay, and nfs_net_kobj frees the allocation first in some of those > cases. p->kobject's timer is then left armed inside freed memory, and > the following splat appears: > > [ 139.805951][ T131] kobject: 'nfs_client' (ffff888027fdb800): kobj= ect_release, parent 0000000000000000 (delayed 300) > [ 139.808019][ T131] kobject: 'net' (ffff888027fdb898): kobject_rel= ease, parent 0000000000000000 (delayed 100) > > BUG: KASAN: slab-use-after-free in __run_timers+0x932/0x980 > Write of size 8 at addr ffff888027fdb868 by task swapper/0/0 > > Reproduced on a KASAN kernel with CONFIG_NFS_FS=3Dy and > CONFIG_DEBUG_KOBJECT_RELEASE=3Dy by: > > for i in $(seq 16); do unshare -n true; done; sleep 20 > > Give p->kobject a reference on nfs_net_kobj for its whole lifetime and > drop it from nfs_netns_client_release(), so the allocation is always > freed after p->kobject has been released. > > Fixes: e96f9268eea6 ("NFS: Make all of /sys/fs/nfs network-namespace un= ique") > Signed-off-by: Vasileios Almpanis Reviewed-by: Benjamin Coddington Ben