Hello, This patchset implements fs-verity for ext4 and f2fs. fs-verity is similar to dm-verity, but implemented on a per-file basis: a Merkle tree is used to measure (hash) the file's data as it is paged in. ext4 and f2fs hide this Merkle tree beyond the end of the file, though other filesystems might implement it differently in the future. In general, fs-verity is intended for use on writable filesystems; dm-verity is still recommended on read-only ones. Similar to fscrypt, most of the code is in fs/verity/, and not too many filesystem-specific changes are needed. The Merkle tree is written by userspace before calling an ioctl to mark the file as a verity file; the file then becomes read-only and the verity metadata is hidden or moved. fs-verity provides a file measurement (hash) in constant time and verifies data on-demand. Thus, it is useful for efficiently verifying the authenticity of large files of which only a small portion may be accessed, such as Android application package (APK) files. It may also be useful in "audit" use cases where file hashes are logged. fs-verity also provides better protection against malicious disks than an ahead-of-time hash, since fs-verity re-verifies data each time it's paged in. Note, however, that any authenticity guarantee is still dependent on verification of the file measurement and other relevant metadata in a way that makes sense for the overall system; fs-verity is only a tool to help with this. This patchset doesn't yet include IMA support for fs-verity file measurements. This is planned and we'd like to collaborate with the IMA maintainers. Although fs-verity can be used on its own without IMA, fs-verity is primarily a lower level feature (think of it as a way of hashing a file), so some users may still need IMA's policy mechanism. However, an optional in-kernel signature verification mechanism within fs-verity itself is also included. This patchset is based on Linus' tree as of today (commit 7c6c54b505b8a). It can also be found in git at tag "fsverity_2018-11-01" of: https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git fs-verity has a userspace utility: https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/fsverity-utils.git xfstests for fs-verity can be found at branch "fsverity" of: https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/xfstests-dev.git fs-verity is supported by e2fsprogs v1.44.4-2+ and f2fs-tools v1.11.0+. Please see the documentation file Documentation/filesystems/fsverity.rst (added by patch 1) for details; this cover letter only gave an overview. Examples of setting up fs-verity protected files can also be found in the README file of fsverity-utils. Other useful references include: - LWN coverage of v1 patchset: https://lwn.net/Articles/763729/ - Presentation at Linux Security Summit North America 2018: - Slides: https://schd.ws/hosted_files/lssna18/af/fs-verity%20slide%20deck.pdf - Video: https://www.youtube.com/watch?v=Aw5h6aBhu6M - Notes from discussion at LSFMM 2018: https://lwn.net/Articles/752614/ Changes since v1: - Added documentation file. - Require write permission for FS_IOC_ENABLE_VERITY, rather than CAP_SYS_ADMIN. - Eliminated dependency on CONFIG_BLOCK and clarified that filesystems can verify a page at a time rather than a bio at a time. - Fixed conditions for verifying holes. - ext4 now only allows fs-verity on extent-based files. - Eliminated most of the assumptions that the verity metadata is stored beyond EOF, in case filesystems want to do things differently. - Other cleanups. Eric Biggers (12): fs-verity: add a documentation file fs-verity: add setup code, UAPI, and Kconfig fs-verity: add MAINTAINERS file entry fs-verity: add data verification hooks for ->readpages() fs-verity: implement FS_IOC_ENABLE_VERITY ioctl fs-verity: implement FS_IOC_MEASURE_VERITY ioctl fs-verity: add SHA-512 support fs-verity: add CRC-32C support fs-verity: support builtin file signatures ext4: add basic fs-verity support ext4: add fs-verity read support f2fs: fs-verity support Documentation/filesystems/fsverity.rst | 583 ++++++++++++++++ Documentation/filesystems/index.rst | 11 + Documentation/ioctl/ioctl-number.txt | 1 + MAINTAINERS | 11 + fs/Kconfig | 2 + fs/Makefile | 1 + fs/ext4/Kconfig | 20 + fs/ext4/ext4.h | 22 +- fs/ext4/file.c | 6 + fs/ext4/inode.c | 11 + fs/ext4/ioctl.c | 12 + fs/ext4/readpage.c | 209 +++++- fs/ext4/super.c | 100 ++- fs/ext4/sysfs.c | 6 + fs/f2fs/Kconfig | 20 + fs/f2fs/data.c | 43 +- fs/f2fs/f2fs.h | 17 +- fs/f2fs/file.c | 58 ++ fs/f2fs/inode.c | 3 +- fs/f2fs/super.c | 30 + fs/f2fs/sysfs.c | 11 + fs/verity/Kconfig | 52 ++ fs/verity/Makefile | 5 + fs/verity/fsverity_private.h | 135 ++++ fs/verity/hash_algs.c | 115 ++++ fs/verity/ioctl.c | 164 +++++ fs/verity/setup.c | 908 +++++++++++++++++++++++++ fs/verity/signature.c | 187 +++++ fs/verity/verify.c | 298 ++++++++ include/linux/fs.h | 9 + include/linux/fsverity.h | 112 +++ include/uapi/linux/fsverity.h | 98 +++ 32 files changed, 3218 insertions(+), 42 deletions(-) create mode 100644 Documentation/filesystems/fsverity.rst create mode 100644 fs/verity/Kconfig create mode 100644 fs/verity/Makefile create mode 100644 fs/verity/fsverity_private.h create mode 100644 fs/verity/hash_algs.c create mode 100644 fs/verity/ioctl.c create mode 100644 fs/verity/setup.c create mode 100644 fs/verity/signature.c create mode 100644 fs/verity/verify.c create mode 100644 include/linux/fsverity.h create mode 100644 include/uapi/linux/fsverity.h -- 2.19.1.568.g152ad8e336-goog
