On Sun, Sep 19, 2021 at 11:44:29PM +0900, Tetsuo Handa wrote: > syzbot is reporting use-after-free read at bdev_free_inode() [1], for > kfree() from __alloc_disk_node() is called before bdev_free_inode() > (which is called after RCU grace period) reads bdev->bd_disk and calls > kfree(bdev->bd_disk). > > Fix use-after-free read followed by double kfree() problem > by explicitly resetting bdev->bd_disk to NULL before calling iput(). > > Link: https://syzkaller.appspot.com/bug?extid=8281086e8a6fbfbd952a [1] > Reported-by: syzbot <syzbot+8281086e8a6fbfbd952a@xxxxxxxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > --- > This patch is not tested due to lack of reproducer. Is this fix correct? > > block/bdev.c | 1 + > block/genhd.c | 1 + > 2 files changed, 2 insertions(+) > > diff --git a/block/bdev.c b/block/bdev.c > index cf2780cb44a7..f6b8bac83bd8 100644 > --- a/block/bdev.c > +++ b/block/bdev.c > @@ -495,6 +495,7 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno) > bdev->bd_inode = inode; > bdev->bd_stats = alloc_percpu(struct disk_stats); > if (!bdev->bd_stats) { > + bdev->bd_disk = NULL; > iput(inode); > return NULL; > } I was going to suggest to just move the bd_disk initialization after the bd_stats allocations, but iseems like we currently don't even the zero the bdev on allocation. So I suspect we should do that first to avoid nasty surprises.
