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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 <boris@bur.io>
Fixes: 3fda4c617e84 ("fs-verity: implement FS_IOC_ENABLE_VERITY ioctl")
Fixes: fd2d1acfcadf ("fs-verity: add the hook for file ->open()")
Cc: <stable@vger.kernel.org> # v5.4+
Reviewed-by: Boris Burkov <boris@bur.io>
Link: https://lore.kernel.org/r/20210916203424.113376-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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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 <victorhsieh@google.com>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Amy Parker <enbyamy@gmail.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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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 <victorhsieh@google.com>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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I originally chose the name "file measurement" to refer to the fs-verity
file digest to avoid confusion with traditional full-file digests or
with the bare root hash of the Merkle tree.
But the name "file measurement" hasn't caught on, and usually people are
calling it something else, usually the "file digest". E.g. see
"struct fsverity_digest" and "struct fsverity_formatted_digest", the
libfsverity_compute_digest() and libfsverity_sign_digest() functions in
libfsverity, and the "fsverity digest" command.
Having multiple names for the same thing is always confusing.
So to hopefully avoid confusion in the future, rename
"fs-verity file measurement" to "fs-verity file digest".
This leaves FS_IOC_MEASURE_VERITY as the only reference to "measure" in
the kernel, which makes some amount of sense since the ioctl is actively
"measuring" the file.
I'll be renaming this in fsverity-utils too (though similarly the
'fsverity measure' command, which is a wrapper for
FS_IOC_MEASURE_VERITY, will stay).
Acked-by: Luca Boccassi <luca.boccassi@microsoft.com>
Link: https://lore.kernel.org/r/20201113211918.71883-4-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Embedding the file path inside kernel source code files isn't
particularly useful as often files are moved around and the paths become
incorrect. checkpatch.pl warns about this since v5.10-rc1.
Acked-by: Luca Boccassi <luca.boccassi@microsoft.com>
Link: https://lore.kernel.org/r/20201113211918.71883-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Normally smp_store_release() or cmpxchg_release() is paired with
smp_load_acquire(). Sometimes smp_load_acquire() can be replaced with
the more lightweight READ_ONCE(). However, for this to be safe, all the
published memory must only be accessed in a way that involves the
pointer itself. This may not be the case if allocating the object also
involves initializing a static or global variable, for example.
fsverity_info::tree_params.hash_alg->tfm is a crypto_ahash object that's
internal to and is allocated by the crypto subsystem. So by using
READ_ONCE() for ->i_verity_info, we're relying on internal
implementation details of the crypto subsystem.
Remove this fragile assumption by using smp_load_acquire() instead.
Also fix the cmpxchg logic to correctly execute an ACQUIRE barrier when
losing the cmpxchg race, since cmpxchg doesn't guarantee a memory
barrier on failure.
(Note: I haven't seen any real-world problems here. This change is just
fixing the code to be guaranteed correct and less fragile.)
Fixes: fd2d1acfcadf ("fs-verity: add the hook for file ->open()")
Link: https://lore.kernel.org/r/20200721225920.114347-6-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Fix all kerneldoc warnings in fs/verity/ and include/linux/fsverity.h.
Most of these were due to missing documentation for function parameters.
Detected with:
scripts/kernel-doc -v -none fs/verity/*.{c,h} include/linux/fsverity.h
This cleanup makes it possible to check new patches for kerneldoc
warnings without having to filter out all the existing ones.
Link: https://lore.kernel.org/r/20200511192118.71427-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
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When initializing an fs-verity hash algorithm, also initialize a mempool
that contains a single preallocated hash request object. Then replace
the direct calls to ahash_request_alloc() and ahash_request_free() with
allocating and freeing from this mempool.
This eliminates the possibility of the allocation failing, which is
desirable for the I/O path.
This doesn't cause deadlocks because there's no case where multiple hash
requests are needed at a time to make forward progress.
Link: https://lore.kernel.org/r/20191231175545.20709-1-ebiggers@kernel.org
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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When fs-verity verifies data pages, currently it reads each Merkle tree
page synchronously using read_mapping_page().
Therefore, when the Merkle tree pages aren't already cached, fs-verity
causes an extra 4 KiB I/O request for every 512 KiB of data (assuming
that the Merkle tree uses SHA-256 and 4 KiB blocks). This results in
more I/O requests and performance loss than is strictly necessary.
Therefore, implement readahead of the Merkle tree pages.
For simplicity, we take advantage of the fact that the kernel already
does readahead of the file's *data*, just like it does for any other
file. Due to this, we don't really need a separate readahead state
(struct file_ra_state) just for the Merkle tree, but rather we just need
to piggy-back on the existing data readahead requests.
We also only really need to bother with the first level of the Merkle
tree, since the usual fan-out factor is 128, so normally over 99% of
Merkle tree I/O requests are for the first level.
Therefore, make fsverity_verify_bio() enable readahead of the first
Merkle tree level, for up to 1/4 the number of pages in the bio, when it
sees that the REQ_RAHEAD flag is set on the bio. The readahead size is
then passed down to ->read_merkle_tree_page() for the filesystem to
(optionally) implement if it sees that the requested page is uncached.
While we're at it, also make build_merkle_tree_level() set the Merkle
tree readahead size, since it's easy to do there.
However, for now don't set the readahead size in fsverity_verify_page(),
since currently it's only used to verify holes on ext4 and f2fs, and it
would need parameters added to know how much to read ahead.
This patch significantly improves fs-verity sequential read performance.
Some quick benchmarks with 'cat'-ing a 250MB file after dropping caches:
On an ARM64 phone (using sha256-ce):
Before: 217 MB/s
After: 263 MB/s
(compare to sha256sum of non-verity file: 357 MB/s)
In an x86_64 VM (using sha256-avx2):
Before: 173 MB/s
After: 215 MB/s
(compare to sha256sum of non-verity file: 223 MB/s)
Link: https://lore.kernel.org/r/20200106205533.137005-1-ebiggers@kernel.org
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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To meet some users' needs, add optional support for having fs-verity
handle a portion of the authentication policy in the kernel. An
".fs-verity" keyring is created to which X.509 certificates can be
added; then a sysctl 'fs.verity.require_signatures' can be set to cause
the kernel to enforce that all fs-verity files contain a signature of
their file measurement by a key in this keyring.
See the "Built-in signature verification" section of
Documentation/filesystems/fsverity.rst for the full documentation.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add functions that verify data pages that have been read from a
fs-verity file, against that file's Merkle tree. These will be called
from filesystems' ->readpage() and ->readpages() methods.
Since data verification can block, a workqueue is provided for these
methods to enqueue verification work from their bio completion callback.
See the "Verifying data" section of
Documentation/filesystems/fsverity.rst for more information.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add a function fsverity_prepare_setattr() which filesystems that support
fs-verity must call to deny truncates of verity files.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Add the fsverity_file_open() function, which prepares an fs-verity file
to be read from. If not already done, it loads the fs-verity descriptor
from the filesystem and sets up an fsverity_info structure for the inode
which describes the Merkle tree and contains the file measurement. It
also denies all attempts to open verity files for writing.
This commit also begins the include/linux/fsverity.h header, which
declares the interface between fs/verity/ and filesystems.
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Eric Biggers
