| Message ID | 20230207011849.1343-1-demi@invisiblethingslab.com (mailing list archive) |
|---|---|
| State | Rejected, archived |
| Delegated to: | Mike Snitzer |
| Headers | show |
| Series | [1/2] Fail I/O to thin pool devices | expand |
Nack. I don't see the security issue; how is this any different from running the thin tools on any incorrect device? Or even the data device that the pool is mirroring. In general the thin tools don't modify the metadata they're running on. If you know of a security issue with the thin tools please let me know. On Tue, Feb 7, 2023 at 7:56 AM Demi Marie Obenour < demi@invisiblethingslab.com> wrote: > A thin pool device currently just passes all I/O to its origin device, > but this is a footgun: the user might not realize that tools that > operate on thin pool metadata must operate on the metadata volume. This > could have security implications. > > Fix this by failing all I/O to thin pool devices. > > Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com> > --- > drivers/md/dm-thin.c | 17 ++++++----------- > 1 file changed, 6 insertions(+), 11 deletions(-) > > diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c > index > 64cfcf46881dc5d87d5dfdb5650ba9babd32cd31..d85fdbd782ae5426003c99a4b4bf53818cc85efa > 100644 > --- a/drivers/md/dm-thin.c > +++ b/drivers/md/dm-thin.c > @@ -3405,19 +3405,14 @@ static int pool_ctr(struct dm_target *ti, unsigned > argc, char **argv) > > static int pool_map(struct dm_target *ti, struct bio *bio) > { > - int r; > - struct pool_c *pt = ti->private; > - struct pool *pool = pt->pool; > - > /* > - * As this is a singleton target, ti->begin is always zero. > + * Previously, access to the pool was passed down to the origin > device. > + * However, this turns out to be error-prone: if the user runs any > of > + * the thin tools on the pool device, the tools could wind up > parsing > + * potentially attacker-controlled data. This mistake has actually > + * happened in practice. Therefore, fail all I/O on the pool > device. > */ > - spin_lock_irq(&pool->lock); > - bio_set_dev(bio, pt->data_dev->bdev); > - r = DM_MAPIO_REMAPPED; > - spin_unlock_irq(&pool->lock); > - > - return r; > + return -EIO; > } > > static int maybe_resize_data_dev(struct dm_target *ti, bool *need_commit) > -- > Sincerely, > Demi Marie Obenour (she/her/hers) > Invisible Things Lab > > -- > dm-devel mailing list > dm-devel@redhat.com > https://listman.redhat.com/mailman/listinfo/dm-devel > > -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
On Tue, Feb 07, 2023 at 03:02:51PM +0000, Joe Thornber wrote: > Nack. > > I don't see the security issue; how is this any different from running the > thin tools on any incorrect device? Or even the data device that the pool > is mirroring. I special-cased the pool device for two reasons: 1. I have run the thin tools on the pool device myself before realising that they needed to be run on the metadata device. It took me a while to realize that I was using the wrong device. I have not made that mistake with other devices, which is why I special-cased the pool device in this patch. 2. Doing I/O to the pool device is pointless. The pool device is strictly slower than the data device and exposes the exact same contents, so accessing the pool device directly is never what one wants. If there are backwards compatibility concerns, I could make this be controlled by a Kconfig option, module parameter, or both. > In general the thin tools don't modify the metadata they're > running on. If you know of a security issue with the thin tools please let > me know. I am not aware of a concrete security problem, but in general I prefer not to expose unnecessary attack surface.
Dne 07. 02. 23 v 17:19 Demi Marie Obenour napsal(a): > On Tue, Feb 07, 2023 at 03:02:51PM +0000, Joe Thornber wrote: >> Nack. >> >> I don't see the security issue; how is this any different from running the >> thin tools on any incorrect device? Or even the data device that the pool >> is mirroring. > > I special-cased the pool device for two reasons: > > 1. I have run the thin tools on the pool device myself before realising > that they needed to be run on the metadata device. It took me a > while to realize that I was using the wrong device. I have not made > that mistake with other devices, which is why I special-cased the > pool device in this patch. > > 2. Doing I/O to the pool device is pointless. The pool device is > strictly slower than the data device and exposes the exact same > contents, so accessing the pool device directly is never what one > wants. > > If there are backwards compatibility concerns, I could make this be > controlled by a Kconfig option, module parameter, or both. > >> In general the thin tools don't modify the metadata they're >> running on. If you know of a security issue with the thin tools please let >> me know. > > I am not aware of a concrete security problem, but in general I prefer > not to expose unnecessary attack surface. lvm2 introduced 'protection' layer device - which keeps -tpool opened and thus avoid possibility to use i.e. mkfs on thin-pool itself (as it requires exclusive open) Zdenek -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c index 64cfcf46881dc5d87d5dfdb5650ba9babd32cd31..d85fdbd782ae5426003c99a4b4bf53818cc85efa 100644 --- a/drivers/md/dm-thin.c +++ b/drivers/md/dm-thin.c @@ -3405,19 +3405,14 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv) static int pool_map(struct dm_target *ti, struct bio *bio) { - int r; - struct pool_c *pt = ti->private; - struct pool *pool = pt->pool; - /* - * As this is a singleton target, ti->begin is always zero. + * Previously, access to the pool was passed down to the origin device. + * However, this turns out to be error-prone: if the user runs any of + * the thin tools on the pool device, the tools could wind up parsing + * potentially attacker-controlled data. This mistake has actually + * happened in practice. Therefore, fail all I/O on the pool device. */ - spin_lock_irq(&pool->lock); - bio_set_dev(bio, pt->data_dev->bdev); - r = DM_MAPIO_REMAPPED; - spin_unlock_irq(&pool->lock); - - return r; + return -EIO; } static int maybe_resize_data_dev(struct dm_target *ti, bool *need_commit)
A thin pool device currently just passes all I/O to its origin device, but this is a footgun: the user might not realize that tools that operate on thin pool metadata must operate on the metadata volume. This could have security implications. Fix this by failing all I/O to thin pool devices. Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com> --- drivers/md/dm-thin.c | 17 ++++++----------- 1 file changed, 6 insertions(+), 11 deletions(-)