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Tue, 13 Oct 2026 05:52:04 -0700 (PDT) Received: from loberman-thinkpadp1gen5.rmtusma.csb ([2600:6c65:2440:d8c:929c:b769:6def:faa3]) by smtp.gmail.com with ESMTPSA id af79cd13be357-93ef5086fe3sm229204385a.37.2026.10.13.05.52.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Oct 2026 05:52:04 -0700 (PDT) Message-ID: Subject: Re: [BUG] scsi: st: use-after-free race between st_remove() and st_open()/scsi_tape_get() From: Laurence Oberman To: Dingisoul Cc: James.Bottomley@HansenPartnership.com, linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, mkp@kernel.org Date: Tue, 13 Oct 2026 08:52:03 -0400 In-Reply-To: <20261012201730.1853897-1-dingiso.kernel@gmail.com> References: <20261007211520.1428497-1-dingiso.kernel@gmail.com> <20261012201730.1853897-1-dingiso.kernel@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-2.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2026-10-12 at 16:17 -0400, Dingisoul wrote: > Hi Laurence, >=20 > Adding you to Cc as requested. Quoting the original report below for > reference; let me know if you'd like anything else re-tested. >=20 > Best, > Dingisoul >=20 > > Hi Kernel Maintainers, > >=20 > > I hit the following report while testing current upstream kernel: > >=20 > > KASAN: slab-use-after-free in st_open > >=20 > > on commit: a90ee4305c4a (2026-10-06) > >=20 > > Root cause: st_remove() drops the device's last reference, and only > > afterwards removes it from st_index_idr: > >=20 > > =C2=A0=C2=A0=C2=A0 static void st_remove(struct scsi_device *SDp) > > =C2=A0=C2=A0=C2=A0 { > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct device *dev =3D &SDp-= >sdev_gendev; > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct scsi_tape *tpnt =3D d= ev_get_drvdata(dev); > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 int index =3D tpnt->index; > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ... > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 mutex_lock(&st_ref_mutex); > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 kref_put(&tpnt->kref, scsi_t= ape_release);=C2=A0 /* may > > kfree(tpnt) right here */ > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 mutex_unlock(&st_ref_mutex); > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 spin_lock(&st_index_lock); > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 idr_remove(&st_index_idr, in= dex);=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* too late: > > tpnt may already be freed */ > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 spin_unlock(&st_index_lock); > > =C2=A0=C2=A0=C2=A0 } > >=20 > > Meanwhile scsi_tape_get() -- called from st_open() on every open of > > a > > tape device node -- looks the device up by the same index and takes > > its > > own reference: > >=20 > > =C2=A0=C2=A0=C2=A0 static struct scsi_tape *scsi_tape_get(int dev) > > =C2=A0=C2=A0=C2=A0 { > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct scsi_tape *STp =3D NU= LL; > >=20 > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 mutex_lock(&st_ref_mutex); > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 spin_lock(&st_index_lock); > >=20 > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 STp =3D idr_find(&st_index_i= dr, dev);=C2=A0 /* can still find the > > freed tpnt */ > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (!STp) goto out; > >=20 > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 kref_get(&STp->kref);=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 /* UAF write */ > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ... > > =C2=A0=C2=A0=C2=A0 } > >=20 > > =C2=A0=C2=A0=C2=A0 static int st_open(struct inode *inode, struct file = *filp) > > =C2=A0=C2=A0=C2=A0 { > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ... > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (!(STp =3D scsi_tape_get(= dev))) { > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ... > >=20 > > Between st_remove()'s mutex_unlock(&st_ref_mutex) and its own > > spin_lock(&st_index_lock), tpnt is already freed but still > > reachable > > through st_index_idr. A concurrent st_open() racing in that window > > takes > > both locks in scsi_tape_get(), finds the stale idr entry, and calls > > kref_get() on the freed tpnt. > >=20 > > We used scsi_debug (ptype=3D1, emulating a tape LUN) to avoid needing > > real > > tape hardware. > >=20 > > The reproducer and .config files are here. > > https://gist.github.com/dingiso/b33f8c01a47bfcbb902d3f21a4877feb > >=20 > > I'm happy to test debug patches or provide additional information. > >=20 > > [=C2=A0=C2=A0 23.212502] > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > [=C2=A0=C2=A0 23.212506] BUG: KASAN: slab-use-after-free in st_open > > (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic- > > instrumented.h:252 ./include/linux/refcount.h:283 > > ./include/linux/refcount.h:366 ./include/linux/refcount.h:383 > > ./include/linux/kref.h:45 drivers/scsi/st.c:254 > > drivers/scsi/st.c:1291) > > [=C2=A0=C2=A0 23.212537] Write of size 4 at addr ffff888009854a1c by ta= sk > > repro/315 > > [=C2=A0=C2=A0 23.212541]=20 > > [=C2=A0=C2=A0 23.212551] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX= + > > PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 > > [=C2=A0=C2=A0 23.212554] Call Trace: > > [=C2=A0=C2=A0 23.212556]=C2=A0 > > [=C2=A0=C2=A0 23.212558]=C2=A0 dump_stack_lvl (lib/dump_stack.c:94 > > lib/dump_stack.c:120) > > [=C2=A0=C2=A0 23.212566]=C2=A0 print_report (mm/kasan/report.c:378 > > mm/kasan/report.c:482) > > [=C2=A0=C2=A0 23.212591]=C2=A0 kasan_report (mm/kasan/report.c:595) > > [=C2=A0=C2=A0 23.212602]=C2=A0 kasan_check_range (mm/kasan/generic.c:18= 6 > > mm/kasan/generic.c:200) > > [=C2=A0=C2=A0 23.212607]=C2=A0 st_open (./include/linux/instrumented.h:= 112 > > ./include/linux/atomic/atomic-instrumented.h:252 > > ./include/linux/refcount.h:283 ./include/linux/refcount.h:366 > > ./include/linux/refcount.h:383 ./include/linux/kref.h:45 > > drivers/scsi/st.c:254 drivers/scsi/st.c:1291) > > [=C2=A0=C2=A0 23.212623]=C2=A0 chrdev_open (fs/char_dev.c:411) > > [=C2=A0=C2=A0 23.212645]=C2=A0 do_dentry_open (fs/open.c:996) > > [=C2=A0=C2=A0 23.212651]=C2=A0 vfs_open (fs/open.c:1101) > > [=C2=A0=C2=A0 23.212656]=C2=A0 path_openat (fs/namei.c:4837 fs/namei.c:= 5000) > > [=C2=A0=C2=A0 23.212669]=C2=A0 do_file_open (fs/namei.c:5029) > > [=C2=A0=C2=A0 23.212693]=C2=A0 do_sys_openat2 (fs/open.c:1417 (discrimi= nator 1)) > > [=C2=A0=C2=A0 23.212702]=C2=A0 __x64_sys_openat (fs/open.c:1423 fs/open= .c:1439 > > fs/open.c:1434 fs/open.c:1434) > > [=C2=A0=C2=A0 23.212712]=C2=A0 do_syscall_64 (arch/x86/entry/syscall_64= .c:61 > > arch/x86/entry/syscall_64.c:84) > > [=C2=A0=C2=A0 23.212719]=C2=A0 entry_SYSCALL_64_after_hwframe > > (arch/x86/entry/entry_64.S:121) > > [=C2=A0=C2=A0 23.212755]=20 > > [=C2=A0=C2=A0 23.212756] Allocated by task 325: > > [=C2=A0=C2=A0 23.212758]=C2=A0 kasan_save_stack (mm/kasan/common.c:57) > > [=C2=A0=C2=A0 23.212764]=C2=A0 kasan_save_track (mm/kasan/common.c:78) > > [=C2=A0=C2=A0 23.212768]=C2=A0 __kasan_kmalloc (mm/kasan/common.c:409 > > mm/kasan/common.c:426) > > [=C2=A0=C2=A0 23.212773]=C2=A0 __kmalloc_cache_noprof (./include/linux/= kasan.h:263 > > mm/slub.c:5563) > > [=C2=A0=C2=A0 23.212778]=C2=A0 st_probe (./include/linux/slab.h:991 > > ./include/linux/slab.h:1312 drivers/scsi/st.c:4376) > > [=C2=A0=C2=A0 23.212783]=C2=A0 really_probe (drivers/base/dd.c:628 > > drivers/base/dd.c:706) > > [=C2=A0=C2=A0 23.212788]=C2=A0 __driver_probe_device (drivers/base/dd.c= :868) > > [=C2=A0=C2=A0 23.212793]=C2=A0 driver_probe_device (drivers/base/dd.c:8= 98) > > [=C2=A0=C2=A0 23.212798]=C2=A0 __device_attach_driver (drivers/base/dd.= c:1026) > > [=C2=A0=C2=A0 23.212803]=C2=A0 bus_for_each_drv (drivers/base/bus.c:500= ) > > [=C2=A0=C2=A0 23.212807]=C2=A0 __device_attach (drivers/base/dd.c:1098) > > [=C2=A0=C2=A0 23.212811]=C2=A0 device_initial_probe (drivers/base/dd.c:= 1153) > > [=C2=A0=C2=A0 23.212816]=C2=A0 bus_probe_device (drivers/base/bus.c:620= ) > > [=C2=A0=C2=A0 23.212821]=C2=A0 device_add (drivers/base/core.c:3776) > > [=C2=A0=C2=A0 23.212826]=C2=A0 scsi_sysfs_add_sdev > > (drivers/scsi/scsi_sysfs.c:1427) > > [=C2=A0=C2=A0 23.212830]=C2=A0 scsi_add_lun (drivers/scsi/scsi_scan.c:1= 138 > > (discriminator 1)) > > [=C2=A0=C2=A0 23.212834]=C2=A0 scsi_probe_and_add_lun > > (drivers/scsi/scsi_scan.c:1311) > > [=C2=A0=C2=A0 23.212838]=C2=A0 __scsi_scan_target (drivers/scsi/scsi_sc= an.c:1805) > > [=C2=A0=C2=A0 23.212841]=C2=A0 scsi_scan_channel (drivers/scsi/scsi_sca= n.c:1895 > > drivers/scsi/scsi_scan.c:1870) > > [=C2=A0=C2=A0 23.212845]=C2=A0 scsi_scan_host_selected > > (drivers/scsi/scsi_scan.c:1924) > > [=C2=A0=C2=A0 23.212849]=C2=A0 scsi_scan_host (drivers/scsi/scsi_scan.c= :2089 > > drivers/scsi/scsi_scan.c:2077) > > [=C2=A0=C2=A0 23.212852] sdebug_driver_probe (drivers/scsi/scsi_debug.c= :9618) > > scsi_debug > > [=C2=A0=C2=A0 23.212875]=C2=A0 really_probe (drivers/base/dd.c:628 > > drivers/base/dd.c:706) > > [=C2=A0=C2=A0 23.212879]=C2=A0 __driver_probe_device (drivers/base/dd.c= :868) > > [=C2=A0=C2=A0 23.212883]=C2=A0 driver_probe_device (drivers/base/dd.c:8= 98) > > [=C2=A0=C2=A0 23.212887]=C2=A0 __device_attach_driver (drivers/base/dd.= c:1026) > > [=C2=A0=C2=A0 23.212891]=C2=A0 bus_for_each_drv (drivers/base/bus.c:500= ) > > [=C2=A0=C2=A0 23.212895]=C2=A0 __device_attach (drivers/base/dd.c:1098) > > [=C2=A0=C2=A0 23.212900]=C2=A0 device_initial_probe (drivers/base/dd.c:= 1153) > > [=C2=A0=C2=A0 23.212905]=C2=A0 bus_probe_device (drivers/base/bus.c:620= ) > > [=C2=A0=C2=A0 23.212909]=C2=A0 device_add (drivers/base/core.c:3776) > > [=C2=A0=C2=A0 23.212914] sdebug_add_host_helper > > (drivers/scsi/scsi_debug.c:8843) scsi_debug > > [=C2=A0=C2=A0 23.212937] add_host_store (drivers/scsi/scsi_debug.c:8878 > > drivers/scsi/scsi_debug.c:8105) scsi_debug > > [=C2=A0=C2=A0 23.212954]=C2=A0 kernfs_fop_write_iter (fs/kernfs/file.c:= 345) > > [=C2=A0=C2=A0 23.212960]=C2=A0 vfs_write (fs/read_write.c:595 fs/read_w= rite.c:687) > > [=C2=A0=C2=A0 23.212964]=C2=A0 ksys_write (fs/read_write.c:739) > > [=C2=A0=C2=A0 23.212968]=C2=A0 do_syscall_64 (arch/x86/entry/syscall_64= .c:61 > > arch/x86/entry/syscall_64.c:84) > > [=C2=A0=C2=A0 23.212973]=C2=A0 entry_SYSCALL_64_after_hwframe > > (arch/x86/entry/entry_64.S:121) > > [=C2=A0=C2=A0 23.212977]=20 > > [=C2=A0=C2=A0 23.212978] Freed by task 325: > > [=C2=A0=C2=A0 23.212980]=C2=A0 kasan_save_stack (mm/kasan/common.c:57) > > [=C2=A0=C2=A0 23.212984]=C2=A0 kasan_save_track (mm/kasan/common.c:78) > > [=C2=A0=C2=A0 23.212989]=C2=A0 kasan_save_free_info (mm/kasan/generic.c= :584) > > [=C2=A0=C2=A0 23.212993]=C2=A0 __kasan_slab_free (mm/kasan/common.c:264 > > mm/kasan/common.c:296) > > [=C2=A0=C2=A0 23.212997]=C2=A0 kfree (./include/linux/kasan.h:235 mm/sl= ub.c:2748 > > mm/slub.c:6509 mm/slub.c:6802) > > [=C2=A0=C2=A0 23.213000]=C2=A0 st_remove (./include/linux/kref.h:65 > > drivers/scsi/st.c:4512) > > [=C2=A0=C2=A0 23.213004]=C2=A0 device_release_driver_internal > > (drivers/base/dd.c:1349 drivers/base/dd.c:1372) > > [=C2=A0=C2=A0 23.213009]=C2=A0 bus_remove_device (drivers/base/bus.c:66= 4) > > [=C2=A0=C2=A0 23.213014]=C2=A0 device_del (drivers/base/core.c:3965) > > [=C2=A0=C2=A0 23.213018]=C2=A0 __scsi_remove_device > > (drivers/scsi/scsi_sysfs.c:1499) > > [=C2=A0=C2=A0 23.213021]=C2=A0 scsi_forget_host (drivers/scsi/scsi_scan= .c:2115) > > [=C2=A0=C2=A0 23.213025]=C2=A0 scsi_remove_host (drivers/scsi/hosts.c:1= 82) > > [=C2=A0=C2=A0 23.213031] sdebug_driver_remove > > (drivers/scsi/scsi_debug.c:9631) scsi_debug > > [=C2=A0=C2=A0 23.213052]=C2=A0 device_release_driver_internal > > (drivers/base/dd.c:1349 drivers/base/dd.c:1372) > > [=C2=A0=C2=A0 23.213057]=C2=A0 bus_remove_device (drivers/base/bus.c:66= 4) > > [=C2=A0=C2=A0 23.213061]=C2=A0 device_del (drivers/base/core.c:3965) > > [=C2=A0=C2=A0 23.213065]=C2=A0 device_unregister (drivers/base/core.c:4= 006) > > [=C2=A0=C2=A0 23.213070] sdebug_do_remove_host > > (drivers/scsi/scsi_debug.c:8917) scsi_debug > > [=C2=A0=C2=A0 23.213089] add_host_store (drivers/scsi/scsi_debug.c:8110= ) > > scsi_debug > > [=C2=A0=C2=A0 23.213109]=C2=A0 kernfs_fop_write_iter (fs/kernfs/file.c:= 345) > > [=C2=A0=C2=A0 23.213113]=C2=A0 vfs_write (fs/read_write.c:595 fs/read_w= rite.c:687) > > [=C2=A0=C2=A0 23.213117]=C2=A0 ksys_write (fs/read_write.c:739) > > [=C2=A0=C2=A0 23.213121]=C2=A0 do_syscall_64 (arch/x86/entry/syscall_64= .c:61 > > arch/x86/entry/syscall_64.c:84) > > [=C2=A0=C2=A0 23.213126]=C2=A0 entry_SYSCALL_64_after_hwframe > > (arch/x86/entry/entry_64.S:121) > > Best, > > Dingisoul Hello Please try this patch, let me know if it fixes this and I will send a follow up to finalize this fix. diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c index f1c3c49466..d5b90bd1c6 100644 --- a/drivers/scsi/st.c +++ b/drivers/scsi/st.c @@ -4509,11 +4509,11 @@ static void st_remove(struct scsi_device *SDp) remove_cdevs(tpnt); =20 mutex_lock(&st_ref_mutex); - kref_put(&tpnt->kref, scsi_tape_release); - mutex_unlock(&st_ref_mutex); spin_lock(&st_index_lock); idr_remove(&st_index_idr, index); spin_unlock(&st_index_lock); + kref_put(&tpnt->kref, scsi_tape_release); + mutex_unlock(&st_ref_mutex); } =20