From: Pavel Skripkin paskripkin@gmail.com
[ Upstream commit b1a811633f7321cf1ae2bb76a66805b7720e44c9 ]
Syzbot hit WARNING in internal_create_group(). The problem was in too big disk->first_minor.
disk->first_minor is initialized by value, which comes from userspace and there wasn't any sanity checks about value correctness. It can cause duplicate creation of sysfs files/links, because disk->first_minor will be passed to MKDEV() which causes truncation to byte. Since maximum minor value is 0xff, let's check if first_minor is correct minor number.
NOTE: the root case of the reported warning was in wrong error handling in register_disk(), but we can avoid passing knowingly wrong values to sysfs API, because sysfs error messages can confuse users. For example: user passed 1048576 as index, but sysfs complains about duplicate creation of /dev/block/43:0. It's not obvious how 1048576 becomes 0. Log and reproducer for above example can be found on syzkaller bug report page.
Link: https://syzkaller.appspot.com/bug?id=03c2ae9146416edf811958d5fd7acfab75b143d... Fixes: b0d9111a2d53 ("nbd: use an idr to keep track of nbd devices") Reported-by: syzbot+9937dc42271cd87d4b98@syzkaller.appspotmail.com Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Pavel Skripkin paskripkin@gmail.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/block/nbd.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 25e81b1a59a5..bc3ab98855cf 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -1744,7 +1744,17 @@ static int nbd_dev_add(int index) refcount_set(&nbd->refs, 1); INIT_LIST_HEAD(&nbd->list); disk->major = NBD_MAJOR; + + /* Too big first_minor can cause duplicate creation of + * sysfs files/links, since first_minor will be truncated to + * byte in __device_add_disk(). + */ disk->first_minor = index << part_shift; + if (disk->first_minor > 0xff) { + err = -EINVAL; + goto out_free_idr; + } + disk->fops = &nbd_fops; disk->private_data = nbd; sprintf(disk->disk_name, "nbd%d", index);