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[5.186.121.52]) by smtp.gmail.com with ESMTPSA id l5sm24606831wrm.66.2020.04.28.03.32.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Apr 2020 03:32:50 -0700 (PDT) Date: Tue, 28 Apr 2020 12:32:49 +0200 From: Javier =?utf-8?B?R29uesOhbGV6?= To: Niklas Cassel Cc: Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg , Igor Konopko , Matias =?utf-8?B?QmrDuHJsaW5n?= , Jens Axboe , "linux-nvme@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] nvme: prevent double free in nvme_alloc_ns() error handling Message-ID: <20200428103249.nrs2lhi2f5oakyrh@mpHalley.local> References: <20200427123443.520469-1-niklas.cassel@wdc.com> <20200427180311.nssquibbak5ib4oo@mpHalley.localdomain> <20200427182245.GA547726@localhost.localdomain> <20200428070651.qbsyivvaakflipr4@mpHalley.localdomain> <20200428074935.GA584449@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200428074935.GA584449@localhost.localdomain> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28.04.2020 07:49, Niklas Cassel wrote: >On Tue, Apr 28, 2020 at 09:06:51AM +0200, Javier González wrote: >> CAUTION: This email originated from outside of Western Digital. Do not click on links or open attachments unless you recognize the sender and know that the content is safe. >> >> >> On 27.04.2020 18:22, Niklas Cassel wrote: >> > On Mon, Apr 27, 2020 at 08:03:11PM +0200, Javier González wrote: >> > > On 27.04.2020 14:34, Niklas Cassel wrote: >> > > > When jumping to the out_put_disk label, we will call put_disk(), which will >> > > > trigger a call to disk_release(), which calls blk_put_queue(). >> > > > >> > > > Later in the cleanup code, we do blk_cleanup_queue(), which will also call >> > > > blk_put_queue(). >> > > > >> > > > Putting the queue twice is incorrect, and will generate a KASAN splat. >> > > > >> > > > Set the disk->queue pointer to NULL, before calling put_disk(), so that the >> > > > first call to blk_put_queue() will not free the queue. >> > > > >> > > > The second call to blk_put_queue() uses another pointer to the same queue, >> > > > so this call will still free the queue. >> > > > >> > > > Fixes: 85136c010285 ("lightnvm: simplify geometry enumeration") >> > > > Signed-off-by: Niklas Cassel >> > > > --- >> > > > drivers/nvme/host/core.c | 2 ++ >> > > > 1 file changed, 2 insertions(+) >> > > > >> > > > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c >> > > > index 91c1bd659947..f2adea96b04c 100644 >> > > > --- a/drivers/nvme/host/core.c >> > > > +++ b/drivers/nvme/host/core.c >> > > > @@ -3642,6 +3642,8 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid) >> > > > >> > > > return; >> > > > out_put_disk: >> > > > + /* prevent double queue cleanup */ >> > > > + ns->disk->queue = NULL; >> > > > put_disk(ns->disk); >> > > > out_unlink_ns: >> > > > mutex_lock(&ctrl->subsys->lock); >> > > > -- >> > > > 2.25.3 >> > > > >> > > What about delaying the assignment of ns->disk? >> > > >> > > diff --git i/drivers/nvme/host/core.c w/drivers/nvme/host/core.c >> > > index a4d8c90ee7cc..6da4a9ced945 100644 >> > > --- i/drivers/nvme/host/core.c >> > > +++ w/drivers/nvme/host/core.c >> > > @@ -3541,7 +3541,6 @@ static int nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid) >> > > disk->queue = ns->queue; >> > > disk->flags = flags; >> > > memcpy(disk->disk_name, disk_name, DISK_NAME_LEN); >> > > - ns->disk = disk; >> > > >> > > __nvme_revalidate_disk(disk, id); >> > > >> > > @@ -3553,6 +3552,8 @@ static int nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid) >> > > } >> > > } >> > > >> > > + ns->disk = disk; >> > > + >> > >> > Hello Javier! >> > >> > >> > The only case where we jump to the out_put_disk label, is if the >> > nvme_nvm_register() call failed. >> > >> > In that case, we want to undo the alloc_disk_node() operation, i.e., >> > decrease the refcount. >> > >> > If we don't set "ns->disk = disk;" before the call to nvme_nvm_register(), >> > then, if register fails, and we jump to the put_disk(ns->disk) label, >> > ns->disk will be NULL, so the recount will not be decreased, so I assume >> > that this memory would then be a memory leak. >> > >> > >> > I think that the problem is that the block functions are a bit messy. >> > Most drivers seem to do blk_cleanup_queue() first and then do put_disk(), >> > but some drivers do it in the opposite way, so I think that we might have >> > some more use-after-free bugs in some of these drivers that do it in the >> > opposite way. >> > >> >> Hi Niklas, >> >> Yes, the out_put_disk label was introduced at the same time as the >> LightNVM entry point. We can do a better job at separating the cleanup >> functions, but as far as I can see ns->disk is not used in the LightNVM >> initialization, so delaying the initialization should be ok. Part of >> this should be also changing the out_put_disk to put_disk(disk). > >Hello Javier, > > >If I understand correctly, you are suggesting this: > >--- a/drivers/nvme/host/core.c >+++ b/drivers/nvme/host/core.c >@@ -3616,7 +3616,6 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid) > disk->queue = ns->queue; > disk->flags = flags; > memcpy(disk->disk_name, disk_name, DISK_NAME_LEN); >- ns->disk = disk; > > __nvme_revalidate_disk(disk, id); > >@@ -3628,6 +3627,8 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid) > } > } > >+ ns->disk = disk; >+ > down_write(&ctrl->namespaces_rwsem); > list_add_tail(&ns->list, &ctrl->namespaces); > up_write(&ctrl->namespaces_rwsem); >@@ -3642,7 +3643,7 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid) > > return; > out_put_disk: >- put_disk(ns->disk); >+ put_disk(disk); > out_unlink_ns: > mutex_lock(&ctrl->subsys->lock); > list_del_rcu(&ns->siblings); > > >That would not solve the double free error when the registration fails, >since disk->queue is still set, so this call will still free the queue. > >Later in the cleanup code blk_cleanup_queue(ns->queue); >is called, which will still try to free what is already freed. > >To remove the double free by delaying assignments, we would need to >delay the assignment of disk->queue until after the LightNVM entry point, >but I don't think that is possible, since __nvme_revalidate_disk(), which >is called before the LightNVM entry point uses disk->queue. > >Christoph said that he would clean up this mess with better block layer >APIs. So perhaps the fix that is already queued is good enough until then. > Makes sense. I see some things have changed in this path since I last looked at it. Thanks! Javier