Messages in this thread | | | Date | Tue, 28 Apr 2020 09:06:51 +0200 | From | Javier González <> | Subject | Re: [PATCH] nvme: prevent double free in nvme_alloc_ns() error handling |
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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 <niklas.cassel@wdc.com> >> > --- >> > 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).
Note that initializing other namespace types here do not require ns->disk either, so delaying initialization should be ok. We have been running with this patch locally for some time.
This said, this is an alternative as your fix works.
Javier
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