On 25.07.2018 16:27, Anand Jain wrote:
> test case btrfs/164 reported UAF..
>
> [ 6712.084324] general protection fault: 0000 [#1] PREEMPT SMP
> ::
> [ 6712.195423] btrfs_update_commit_device_size+0x75/0xf0 [btrfs]
> [ 6712.201424] btrfs_commit_transaction+0x57d/0xa90 [btrfs]
> [ 6712.206999] btrfs_rm_device+0x627/0x850 [btrfs]
> [ 6712.211800] btrfs_ioctl+0x2b03/0x3120 [btrfs]
> ::
>
> reason for this is that btrfs_shrink_device() adds the device resized to
> the fs_devices::resized_devices after it has called the last commit
> transaction.
> So the list fs_devices::resized_devices is not empty when
> btrfs_shrink_device() returns.
> Now the parent function btrfs_rm_device() calls
> btrfs_close_bdev(device);
> call_rcu(&device->rcu, free_device_rcu);
> and then does the commit transaction.
> The commit transaction goes through the fs_devices::resized_devices
> in btrfs_update_commit_device_size() and leads to UAF.
>
> Fix this by making sure btrfs_shrink_device() calls the last needed
> btrfs_commit_transaction() before the return.
>
> Signed-off-by: Anand Jain <anand.j...@oracle.com>
> ---
> I am bit skeptical about the condition when btrfs_commit_transaction()
> fails, can you pls be wary about it when reviewing. Thanks.
>
> Lu/David,
> As this issues isn't reproducible at my end, can you pls test this
> patch on top of the patch
> btrfs: fix missing superblock update in the device delete commit transaction
> Thanks.
>
> fs/btrfs/volumes.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 418843b8f8e8..344083cc811c 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -4464,7 +4464,10 @@ int btrfs_shrink_device(struct btrfs_device *device,
> u64 new_size)
>
> /* Now btrfs_update_device() will change the on-disk size. */
> ret = btrfs_update_device(trans, device);
> - btrfs_end_transaction(trans);
> + if (ret)
> + btrfs_end_transaction(trans);
Why don't you call btrfs_abort_transaction on error from
btrfs_update_device?
> + else
> + ret = btrfs_commit_transaction(trans);
> done:
> btrfs_free_path(path);
> if (ret) {
>
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