starfive-tech/linux.git/fs/verity, branch rt-linux-release

fs-verity: fix signed integer overflow with i_size near S64_MAX

2021-09-22T17:56:34+00:00

If the file size is almost S64_MAX, the calculated number of Merkle tree levels exceeds FS_VERITY_MAX_LEVELS, causing FS_IOC_ENABLE_VERITY to fail. This is unintentional, since as the comment above the definition of FS_VERITY_MAX_LEVELS states, it is enough for over U64_MAX bytes of data using SHA-256 and 4K blocks. (Specifically, 4096*128**8 >= 2**64.) The bug is actually that when the number of blocks in the first level is calculated from i_size, there is a signed integer overflow due to i_size being signed. Fix this by treating i_size as unsigned. This was found by the new test "generic: test fs-verity EFBIG scenarios" (https://lkml.kernel.org/r/b1d116cd4d0ea74b9cd86f349c672021e005a75c.1631558495.git.boris@bur.io). This didn't affect ext4 or f2fs since those have a smaller maximum file size, but it did affect btrfs which allows files up to S64_MAX bytes. Reported-by: Boris Burkov Fixes: 3fda4c617e84 ("fs-verity: implement FS_IOC_ENABLE_VERITY ioctl") Fixes: fd2d1acfcadf ("fs-verity: add the hook for file ->open()") Cc: # v5.4+ Reviewed-by: Boris Burkov Link: https://lore.kernel.org/r/20210916203424.113376-1-ebiggers@kernel.org Signed-off-by: Eric Biggers

fsverity: relax build time dependency on CRYPTO_SHA256

2021-04-22T07:31:32+00:00

CONFIG_CRYPTO_SHA256 denotes the generic C implementation of the SHA-256 shash algorithm, which is selected as the default crypto shash provider for fsverity. However, fsverity has no strict link time dependency, and the same shash could be exposed by an optimized implementation, and arm64 has a number of those (scalar, NEON-based and one based on special crypto instructions). In such cases, it makes little sense to require that the generic C implementation is incorporated as well, given that it will never be called. To address this, relax the 'select' clause to 'imply' so that the generic driver can be omitted from the build if desired. Acked-by: Eric Biggers Signed-off-by: Ard Biesheuvel Signed-off-by: Herbert Xu

Merge tag 'idmapped-mounts-v5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

2021-02-23T21:39:45+00:00

Pull idmapped mounts from Christian Brauner: "This introduces idmapped mounts which has been in the making for some time. Simply put, different mounts can expose the same file or directory with different ownership. This initial implementation comes with ports for fat, ext4 and with Christoph's port for xfs with more filesystems being actively worked on by independent people and maintainers. Idmapping mounts handle a wide range of long standing use-cases. Here are just a few: - Idmapped mounts make it possible to easily share files between multiple users or multiple machines especially in complex scenarios. For example, idmapped mounts will be used in the implementation of portable home directories in systemd-homed.service(8) where they allow users to move their home directory to an external storage device and use it on multiple computers where they are assigned different uids and gids. This effectively makes it possible to assign random uids and gids at login time. - It is possible to share files from the host with unprivileged containers without having to change ownership permanently through chown(2). - It is possible to idmap a container's rootfs and without having to mangle every file. For example, Chromebooks use it to share the user's Download folder with their unprivileged containers in their Linux subsystem. - It is possible to share files between containers with non-overlapping idmappings. - Filesystem that lack a proper concept of ownership such as fat can use idmapped mounts to implement discretionary access (DAC) permission checking. - They allow users to efficiently changing ownership on a per-mount basis without having to (recursively) chown(2) all files. In contrast to chown (2) changing ownership of large sets of files is instantenous with idmapped mounts. This is especially useful when ownership of a whole root filesystem of a virtual machine or container is changed. With idmapped mounts a single syscall mount_setattr syscall will be sufficient to change the ownership of all files. - Idmapped mounts always take the current ownership into account as idmappings specify what a given uid or gid is supposed to be mapped to. This contrasts with the chown(2) syscall which cannot by itself take the current ownership of the files it changes into account. It simply changes the ownership to the specified uid and gid. This is especially problematic when recursively chown(2)ing a large set of files which is commong with the aforementioned portable home directory and container and vm scenario. - Idmapped mounts allow to change ownership locally, restricting it to specific mounts, and temporarily as the ownership changes only apply as long as the mount exists. Several userspace projects have either already put up patches and pull-requests for this feature or will do so should you decide to pull this: - systemd: In a wide variety of scenarios but especially right away in their implementation of portable home directories. https://systemd.io/HOME_DIRECTORY/ - container runtimes: containerd, runC, LXD:To share data between host and unprivileged containers, unprivileged and privileged containers, etc. The pull request for idmapped mounts support in containerd, the default Kubernetes runtime is already up for quite a while now: https://github.com/containerd/containerd/pull/4734 - The virtio-fs developers and several users have expressed interest in using this feature with virtual machines once virtio-fs is ported. - ChromeOS: Sharing host-directories with unprivileged containers. I've tightly synced with all those projects and all of those listed here have also expressed their need/desire for this feature on the mailing list. For more info on how people use this there's a bunch of talks about this too. Here's just two recent ones: https://www.cncf.io/wp-content/uploads/2020/12/Rootless-Containers-in-Gitpod.pdf https://fosdem.org/2021/schedule/event/containers_idmap/ This comes with an extensive xfstests suite covering both ext4 and xfs: https://git.kernel.org/brauner/xfstests-dev/h/idmapped_mounts It covers truncation, creation, opening, xattrs, vfscaps, setid execution, setgid inheritance and more both with idmapped and non-idmapped mounts. It already helped to discover an unrelated xfs setgid inheritance bug which has since been fixed in mainline. It will be sent for inclusion with the xfstests project should you decide to merge this. In order to support per-mount idmappings vfsmounts are marked with user namespaces. The idmapping of the user namespace will be used to map the ids of vfs objects when they are accessed through that mount. By default all vfsmounts are marked with the initial user namespace. The initial user namespace is used to indicate that a mount is not idmapped. All operations behave as before and this is verified in the testsuite. Based on prior discussions we want to attach the whole user namespace and not just a dedicated idmapping struct. This allows us to reuse all the helpers that already exist for dealing with idmappings instead of introducing a whole new range of helpers. In addition, if we decide in the future that we are confident enough to enable unprivileged users to setup idmapped mounts the permission checking can take into account whether the caller is privileged in the user namespace the mount is currently marked with. The user namespace the mount will be marked with can be specified by passing a file descriptor refering to the user namespace as an argument to the new mount_setattr() syscall together with the new MOUNT_ATTR_IDMAP flag. The system call follows the openat2() pattern of extensibility. The following conditions must be met in order to create an idmapped mount: - The caller must currently have the CAP_SYS_ADMIN capability in the user namespace the underlying filesystem has been mounted in. - The underlying filesystem must support idmapped mounts. - The mount must not already be idmapped. This also implies that the idmapping of a mount cannot be altered once it has been idmapped. - The mount must be a detached/anonymous mount, i.e. it must have been created by calling open_tree() with the OPEN_TREE_CLONE flag and it must not already have been visible in the filesystem. The last two points guarantee easier semantics for userspace and the kernel and make the implementation significantly simpler. By default vfsmounts are marked with the initial user namespace and no behavioral or performance changes are observed. The manpage with a detailed description can be found here: https://git.kernel.org/brauner/man-pages/c/1d7b902e2875a1ff342e036a9f866a995640aea8 In order to support idmapped mounts, filesystems need to be changed and mark themselves with the FS_ALLOW_IDMAP flag in fs_flags. The patches to convert individual filesystem are not very large or complicated overall as can be seen from the included fat, ext4, and xfs ports. Patches for other filesystems are actively worked on and will be sent out separately. The xfstestsuite can be used to verify that port has been done correctly. The mount_setattr() syscall is motivated independent of the idmapped mounts patches and it's been around since July 2019. One of the most valuable features of the new mount api is the ability to perform mounts based on file descriptors only. Together with the lookup restrictions available in the openat2() RESOLVE_* flag namespace which we added in v5.6 this is the first time we are close to hardened and race-free (e.g. symlinks) mounting and path resolution. While userspace has started porting to the new mount api to mount proper filesystems and create new bind-mounts it is currently not possible to change mount options of an already existing bind mount in the new mount api since the mount_setattr() syscall is missing. With the addition of the mount_setattr() syscall we remove this last restriction and userspace can now fully port to the new mount api, covering every use-case the old mount api could. We also add the crucial ability to recursively change mount options for a whole mount tree, both removing and adding mount options at the same time. This syscall has been requested multiple times by various people and projects. There is a simple tool available at https://github.com/brauner/mount-idmapped that allows to create idmapped mounts so people can play with this patch series. I'll add support for the regular mount binary should you decide to pull this in the following weeks: Here's an example to a simple idmapped mount of another user's home directory: u1001@f2-vm:/$ sudo ./mount --idmap both:1000:1001:1 /home/ubuntu/ /mnt u1001@f2-vm:/$ ls -al /home/ubuntu/ total 28 drwxr-xr-x 2 ubuntu ubuntu 4096 Oct 28 22:07 . drwxr-xr-x 4 root root 4096 Oct 28 04:00 .. -rw------- 1 ubuntu ubuntu 3154 Oct 28 22:12 .bash_history -rw-r--r-- 1 ubuntu ubuntu 220 Feb 25 2020 .bash_logout -rw-r--r-- 1 ubuntu ubuntu 3771 Feb 25 2020 .bashrc -rw-r--r-- 1 ubuntu ubuntu 807 Feb 25 2020 .profile -rw-r--r-- 1 ubuntu ubuntu 0 Oct 16 16:11 .sudo_as_admin_successful -rw------- 1 ubuntu ubuntu 1144 Oct 28 00:43 .viminfo u1001@f2-vm:/$ ls -al /mnt/ total 28 drwxr-xr-x 2 u1001 u1001 4096 Oct 28 22:07 . drwxr-xr-x 29 root root 4096 Oct 28 22:01 .. -rw------- 1 u1001 u1001 3154 Oct 28 22:12 .bash_history -rw-r--r-- 1 u1001 u1001 220 Feb 25 2020 .bash_logout -rw-r--r-- 1 u1001 u1001 3771 Feb 25 2020 .bashrc -rw-r--r-- 1 u1001 u1001 807 Feb 25 2020 .profile -rw-r--r-- 1 u1001 u1001 0 Oct 16 16:11 .sudo_as_admin_successful -rw------- 1 u1001 u1001 1144 Oct 28 00:43 .viminfo u1001@f2-vm:/$ touch /mnt/my-file u1001@f2-vm:/$ setfacl -m u:1001:rwx /mnt/my-file u1001@f2-vm:/$ sudo setcap -n 1001 cap_net_raw+ep /mnt/my-file u1001@f2-vm:/$ ls -al /mnt/my-file -rw-rwxr--+ 1 u1001 u1001 0 Oct 28 22:14 /mnt/my-file u1001@f2-vm:/$ ls -al /home/ubuntu/my-file -rw-rwxr--+ 1 ubuntu ubuntu 0 Oct 28 22:14 /home/ubuntu/my-file u1001@f2-vm:/$ getfacl /mnt/my-file getfacl: Removing leading '/' from absolute path names # file: mnt/my-file # owner: u1001 # group: u1001 user::rw- user:u1001:rwx group::rw- mask::rwx other::r-- u1001@f2-vm:/$ getfacl /home/ubuntu/my-file getfacl: Removing leading '/' from absolute path names # file: home/ubuntu/my-file # owner: ubuntu # group: ubuntu user::rw- user:ubuntu:rwx group::rw- mask::rwx other::r--" * tag 'idmapped-mounts-v5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux: (41 commits) xfs: remove the possibly unused mp variable in xfs_file_compat_ioctl xfs: support idmapped mounts ext4: support idmapped mounts fat: handle idmapped mounts tests: add mount_setattr() selftests fs: introduce MOUNT_ATTR_IDMAP fs: add mount_setattr() fs: add attr_flags_to_mnt_flags helper fs: split out functions to hold writers namespace: only take read lock in do_reconfigure_mnt() mount: make {lock,unlock}_mount_hash() static namespace: take lock_mount_hash() directly when changing flags nfs: do not export idmapped mounts overlayfs: do not mount on top of idmapped mounts ecryptfs: do not mount on top of idmapped mounts ima: handle idmapped mounts apparmor: handle idmapped mounts fs: make helpers idmap mount aware exec: handle idmapped mounts would_dump: handle idmapped mounts ...

fs-verity: support reading signature with ioctl

2021-02-07T22:51:19+00:00

Add support for FS_VERITY_METADATA_TYPE_SIGNATURE to FS_IOC_READ_VERITY_METADATA. This allows a userspace server program to retrieve the built-in signature (if present) of a verity file for serving to a client which implements fs-verity compatible verification. See the patch which introduced FS_IOC_READ_VERITY_METADATA for more details. The ability for userspace to read the built-in signatures is also useful because it allows a system that is using the in-kernel signature verification to migrate to userspace signature verification. This has been tested using a new xfstest which calls this ioctl via a new subcommand for the 'fsverity' program from fsverity-utils. Link: https://lore.kernel.org/r/20210115181819.34732-7-ebiggers@kernel.org Reviewed-by: Victor Hsieh Reviewed-by: Jaegeuk Kim Reviewed-by: Chao Yu Signed-off-by: Eric Biggers

fs-verity: support reading descriptor with ioctl

2021-02-07T22:51:17+00:00

Add support for FS_VERITY_METADATA_TYPE_DESCRIPTOR to FS_IOC_READ_VERITY_METADATA. This allows a userspace server program to retrieve the fs-verity descriptor of a file for serving to a client which implements fs-verity compatible verification. See the patch which introduced FS_IOC_READ_VERITY_METADATA for more details. "fs-verity descriptor" here means only the part that userspace cares about because it is hashed to produce the file digest. It doesn't include the signature which ext4 and f2fs append to the fsverity_descriptor struct when storing it on-disk, since that way of storing the signature is an implementation detail. The next patch adds a separate metadata_type value for retrieving the signature separately. This has been tested using a new xfstest which calls this ioctl via a new subcommand for the 'fsverity' program from fsverity-utils. Link: https://lore.kernel.org/r/20210115181819.34732-6-ebiggers@kernel.org Reviewed-by: Victor Hsieh Reviewed-by: Jaegeuk Kim Reviewed-by: Chao Yu Signed-off-by: Eric Biggers

fs-verity: support reading Merkle tree with ioctl

2021-02-07T22:51:14+00:00

Add support for FS_VERITY_METADATA_TYPE_MERKLE_TREE to FS_IOC_READ_VERITY_METADATA. This allows a userspace server program to retrieve the Merkle tree of a verity file for serving to a client which implements fs-verity compatible verification. See the patch which introduced FS_IOC_READ_VERITY_METADATA for more details. This has been tested using a new xfstest which calls this ioctl via a new subcommand for the 'fsverity' program from fsverity-utils. Link: https://lore.kernel.org/r/20210115181819.34732-5-ebiggers@kernel.org Reviewed-by: Victor Hsieh Reviewed-by: Jaegeuk Kim Reviewed-by: Chao Yu Signed-off-by: Eric Biggers

fs-verity: add FS_IOC_READ_VERITY_METADATA ioctl

2021-02-07T22:51:11+00:00

Add an ioctl FS_IOC_READ_VERITY_METADATA which will allow reading verity metadata from a file that has fs-verity enabled, including: - The Merkle tree - The fsverity_descriptor (not including the signature if present) - The built-in signature, if present This ioctl has similar semantics to pread(). It is passed the type of metadata to read (one of the above three), and a buffer, offset, and size. It returns the number of bytes read or an error. Separate patches will add support for each of the above metadata types. This patch just adds the ioctl itself. This ioctl doesn't make any assumption about where the metadata is stored on-disk. It does assume the metadata is in a stable format, but that's basically already the case: - The Merkle tree and fsverity_descriptor are defined by how fs-verity file digests are computed; see the "File digest computation" section of Documentation/filesystems/fsverity.rst. Technically, the way in which the levels of the tree are ordered relative to each other wasn't previously specified, but it's logical to put the root level first. - The built-in signature is the value passed to FS_IOC_ENABLE_VERITY. This ioctl is useful because it allows writing a server program that takes a verity file and serves it to a client program, such that the client can do its own fs-verity compatible verification of the file. This only makes sense if the client doesn't trust the server and if the server needs to provide the storage for the client. More concretely, there is interest in using this ability in Android to export APK files (which are protected by fs-verity) to "protected VMs". This would use Protected KVM (https://lwn.net/Articles/836693), which provides an isolated execution environment without having to trust the traditional "host". A "guest" VM can boot from a signed image and perform specific tasks in a minimum trusted environment using files that have fs-verity enabled on the host, without trusting the host or requiring that the guest has its own trusted storage. Technically, it would be possible to duplicate the metadata and store it in separate files for serving. However, that would be less efficient and would require extra care in userspace to maintain file consistency. In addition to the above, the ability to read the built-in signatures is useful because it allows a system that is using the in-kernel signature verification to migrate to userspace signature verification. Link: https://lore.kernel.org/r/20210115181819.34732-4-ebiggers@kernel.org Reviewed-by: Victor Hsieh Acked-by: Jaegeuk Kim Reviewed-by: Chao Yu Signed-off-by: Eric Biggers

fs-verity: don't pass whole descriptor to fsverity_verify_signature()

2021-02-07T22:51:09+00:00

Now that fsverity_get_descriptor() validates the sig_size field, fsverity_verify_signature() doesn't need to do it. Just change the prototype of fsverity_verify_signature() to take the signature directly rather than take a fsverity_descriptor. Link: https://lore.kernel.org/r/20210115181819.34732-3-ebiggers@kernel.org Reviewed-by: Victor Hsieh Reviewed-by: Jaegeuk Kim Reviewed-by: Amy Parker Reviewed-by: Chao Yu Signed-off-by: Eric Biggers

fs-verity: factor out fsverity_get_descriptor()

2021-02-07T22:51:03+00:00

The FS_IOC_READ_VERITY_METADATA ioctl will need to return the fs-verity descriptor (and signature) to userspace. There are a few ways we could implement this: - Save a copy of the descriptor (and signature) in the fsverity_info struct that hangs off of the in-memory inode. However, this would waste memory since most of the time it wouldn't be needed. - Regenerate the descriptor from the merkle_tree_params in the fsverity_info. However, this wouldn't work for the signature, nor for the salt which the merkle_tree_params only contains indirectly as part of the 'hashstate'. It would also be error-prone. - Just get them from the filesystem again. The disadvantage is that in general we can't trust that they haven't been maliciously changed since the file has opened. However, the use cases for FS_IOC_READ_VERITY_METADATA don't require that it verifies the chain of trust. So this is okay as long as we do some basic validation. In preparation for implementing the third option, factor out a helper function fsverity_get_descriptor() which gets the descriptor (and appended signature) from the filesystem and does some basic validation. As part of this, start checking the sig_size field for overflow. Currently fsverity_verify_signature() does this. But the new ioctl will need this too, so do it earlier. Link: https://lore.kernel.org/r/20210115181819.34732-2-ebiggers@kernel.org Reviewed-by: Victor Hsieh Reviewed-by: Jaegeuk Kim Reviewed-by: Chao Yu Signed-off-by: Eric Biggers

fs: add file and path permissions helpers

2021-01-24T13:27:16+00:00

Add two simple helpers to check permissions on a file and path respectively and convert over some callers. It simplifies quite a few codepaths and also reduces the churn in later patches quite a bit. Christoph also correctly points out that this makes codepaths (e.g. ioctls) way easier to follow that would otherwise have to do more complex argument passing than necessary. Link: https://lore.kernel.org/r/20210121131959.646623-4-christian.brauner@ubuntu.com Cc: David Howells Cc: Al Viro Cc: linux-fsdevel@vger.kernel.org Suggested-by: Christoph Hellwig Reviewed-by: Christoph Hellwig Reviewed-by: James Morris Signed-off-by: Christian Brauner