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block: nbd: add sanity check for first_minor

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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=03c2ae9146416edf811958d5fd7acfab75b143d1
Fixes: b0d9111a2d ("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>
This commit is contained in:
Pavel Skripkin 2021-08-12 12:15:01 +03:00 committed by Jens Axboe
parent 9ea9b9c483
commit b1a811633f
1 changed files with 10 additions and 0 deletions
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10
drivers/block/nbd.c
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@ -1750,7 +1750,17 @@ static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
refcount_set(&nbd->refs, refs);
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->minors = 1 << part_shift;
disk->fops = &nbd_fops;
disk->private_data = nbd;