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Note that we got 3 patches for this syzbot warning from 3 different people. Please, cooperate next time and send just one patch. Mikulas On Mon, 26 Oct 2026, Eduard Zateev wrote: > From: angel > > The thin-pool target rejects identical argument strings, but two names for > the same block device bypass the check. In read-only metadata mode, opening > metadata first and data with write mode invokes dm_get_device() > upgrade_mode(). > That swaps and frees the old dm_dev while pool_ctr retains metadata_dev, > causing a slab-use-after-free when __pool_find() reads metadata_dev->bdev. > > Open the data device before metadata so an alias cannot trigger a mode > upgrade between the two references. Compare the opened block devices > and reject aliases before using either device. Adjust the error paths to > release the devices in the matching order. > > Reported-by: syzbot+83827f9a59abe148bff4@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=83827f9a59abe148bff4 > Fixes: 70de2cbda8a5 ("dm thin: add sanity checks to thin-pool and external snapshot creation") > Signed-off-by: Eduard Zateev > --- > drivers/md/dm-thin.c | 21 ++++++++++++++------- > 1 file changed, 14 insertions(+), 7 deletions(-) > > diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c > index 358ed77ff..0899cbaf9 100644 > --- a/drivers/md/dm-thin.c > +++ b/drivers/md/dm-thin.c > @@ -3326,17 +3326,24 @@ static int pool_ctr(struct dm_target *ti, unsigned int argc, char **argv) > > metadata_mode = BLK_OPEN_READ | > ((pf.mode == PM_READ_ONLY) ? 0 : BLK_OPEN_WRITE); > + r = dm_get_device(ti, argv[1], BLK_OPEN_READ | BLK_OPEN_WRITE, &data_dev); > + if (r) { > + ti->error = "Error getting data device"; > + goto out_unlock; > + } > + > r = dm_get_device(ti, argv[0], metadata_mode, &metadata_dev); > if (r) { > ti->error = "Error opening metadata block device"; > - goto out_unlock; > + goto out_data; > } > warn_if_metadata_device_too_big(metadata_dev->bdev); > > - r = dm_get_device(ti, argv[1], BLK_OPEN_READ | BLK_OPEN_WRITE, &data_dev); > - if (r) { > - ti->error = "Error getting data device"; > - goto out_metadata; > + /* make sure metadata and data are different devices */ > + if (metadata_dev->bdev == data_dev->bdev) { > + ti->error = "Error setting metadata or data device"; > + r = -EINVAL; > + goto out; > } > > if (kstrtoul(argv[2], 10, &block_size) || !block_size || > @@ -3426,9 +3433,9 @@ static int pool_ctr(struct dm_target *ti, unsigned int argc, char **argv) > out_free_pt: > kfree(pt); > out: > - dm_put_device(ti, data_dev); > -out_metadata: > dm_put_device(ti, metadata_dev); > +out_data: > + dm_put_device(ti, data_dev); > out_unlock: > mutex_unlock(&dm_thin_pool_table.mutex); > > > base-commit: 21a7f44fd0765fcc5194130b28767786eba1d1e7 > -- > 2.56.0 >